[PATCHv6,1/3] drm: add support for DisplayPort CEC-Tunneling-over-AUX

Submitted by Hans Verkuil on June 12, 2018, 11:18 a.m.

Details

Message ID 20180612111831.58210-2-hverkuil@xs4all.nl
State New
Headers show
Series "drm/i915: add DisplayPort CEC-Tunneling-over-AUX support" ( rev: 7 ) in DRI devel

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Commit Message

Hans Verkuil June 12, 2018, 11:18 a.m.
From: Hans Verkuil <hans.verkuil@cisco.com>

This adds support for the DisplayPort CEC-Tunneling-over-AUX
feature that is part of the DisplayPort 1.3 standard.

Unfortunately, not all DisplayPort/USB-C to HDMI adapters with a
chip that has this capability actually hook up the CEC pin, so
even though a CEC device is created, it may not actually work.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
---
 drivers/gpu/drm/Kconfig         |  10 +
 drivers/gpu/drm/Makefile        |   1 +
 drivers/gpu/drm/drm_dp_cec.c    | 423 ++++++++++++++++++++++++++++++++
 drivers/gpu/drm/drm_dp_helper.c |   1 +
 include/drm/drm_dp_helper.h     |  56 +++++
 5 files changed, 491 insertions(+)
 create mode 100644 drivers/gpu/drm/drm_dp_cec.c

Patch hide | download patch | download mbox

diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
index deeefa7a1773..d63876425cdc 100644
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -121,6 +121,16 @@  config DRM_LOAD_EDID_FIRMWARE
 	  default case is N. Details and instructions how to build your own
 	  EDID data are given in Documentation/EDID/HOWTO.txt.
 
+config DRM_DP_CEC
+	bool "Enable DisplayPort CEC-Tunneling-over-AUX HDMI support"
+	select CEC_CORE
+	help
+	  Choose this option if you want to enable HDMI CEC support for
+	  DisplayPort/USB-C to HDMI adapters.
+
+	  Note: not all adapters support this feature, and even for those
+	  that do support this they often do not hook up the CEC pin.
+
 config DRM_TTM
 	tristate
 	depends on DRM && MMU
diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
index 50093ff4479b..c787481c2502 100644
--- a/drivers/gpu/drm/Makefile
+++ b/drivers/gpu/drm/Makefile
@@ -41,6 +41,7 @@  drm_kms_helper-$(CONFIG_DRM_PANEL_BRIDGE) += bridge/panel.o
 drm_kms_helper-$(CONFIG_DRM_FBDEV_EMULATION) += drm_fb_helper.o
 drm_kms_helper-$(CONFIG_DRM_KMS_CMA_HELPER) += drm_fb_cma_helper.o
 drm_kms_helper-$(CONFIG_DRM_DP_AUX_CHARDEV) += drm_dp_aux_dev.o
+drm_kms_helper-$(CONFIG_DRM_DP_CEC) += drm_dp_cec.o
 
 obj-$(CONFIG_DRM_KMS_HELPER) += drm_kms_helper.o
 obj-$(CONFIG_DRM_DEBUG_MM_SELFTEST) += selftests/
diff --git a/drivers/gpu/drm/drm_dp_cec.c b/drivers/gpu/drm/drm_dp_cec.c
new file mode 100644
index 000000000000..555a9fca3fef
--- /dev/null
+++ b/drivers/gpu/drm/drm_dp_cec.c
@@ -0,0 +1,423 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * DisplayPort CEC-Tunneling-over-AUX support
+ *
+ * Copyright 2018 Cisco Systems, Inc. and/or its affiliates. All rights reserved.
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <drm/drm_dp_helper.h>
+#include <media/cec.h>
+
+/*
+ * Unfortunately it turns out that we have a chicken-and-egg situation
+ * here. Quite a few active (mini-)DP-to-HDMI or USB-C-to-HDMI adapters
+ * have a converter chip that supports CEC-Tunneling-over-AUX (usually the
+ * Parade PS176), but they do not wire up the CEC pin, thus making CEC
+ * useless.
+ *
+ * Sadly there is no way for this driver to know this. What happens is
+ * that a /dev/cecX device is created that is isolated and unable to see
+ * any of the other CEC devices. Quite literally the CEC wire is cut
+ * (or in this case, never connected in the first place).
+ *
+ * The reason so few adapters support this is that this tunneling protocol
+ * was never supported by any OS. So there was no easy way of testing it,
+ * and no incentive to correctly wire up the CEC pin.
+ *
+ * Hopefully by creating this driver it will be easier for vendors to
+ * finally fix their adapters and test the CEC functionality.
+ *
+ * I keep a list of known working adapters here:
+ *
+ * https://hverkuil.home.xs4all.nl/cec-status.txt
+ *
+ * Please mail me (hverkuil@xs4all.nl) if you find an adapter that works
+ * and is not yet listed there.
+ *
+ * Note that the current implementation does not support CEC over an MST hub.
+ * As far as I can see there is no mechanism defined in the DisplayPort
+ * standard to transport CEC interrupts over an MST device. It might be
+ * possible to do this through polling, but I have not been able to get that
+ * to work.
+ */
+
+/**
+ * DOC: dp cec helpers
+ *
+ * These functions take care of supporting the CEC-Tunneling-over-AUX
+ * feature of DisplayPort-to-HDMI adapters.
+ */
+
+/*
+ * When the EDID is unset because the HPD went low, then the CEC DPCD registers
+ * typically can no longer be read (true for a DP-to-HDMI adapter since it is
+ * powered by the HPD). However, some displays toggle the HPD off and on for a
+ * short period for one reason or another, and that would cause the CEC adapter
+ * to be removed and added again, even though nothing else changed.
+ *
+ * This module parameter sets a delay in seconds before the CEC adapter is
+ * actually unregistered. Only if the HPD does not return within that time will
+ * the CEC adapter be unregistered.
+ *
+ * If it is set to 0, then the CEC adapter will never be unregistered for as
+ * long as the connector remains registered.
+ *
+ * Note that for integrated HDMI branch devices that support CEC the DPCD
+ * registers remain available even if the HPD goes low since it is not powered
+ * by the HPD. In that case the CEC adapter will never be unregistered during
+ * the life time of the connector. At least, this is the theory since I do not
+ * have hardware with an integrated HDMI branch device that supports CEC.
+ */
+static unsigned int drm_dp_cec_unregister_delay = 1;
+module_param(drm_dp_cec_unregister_delay, uint, 0600);
+MODULE_PARM_DESC(drm_dp_cec_unregister_delay, "CEC unregister delay in seconds, 0 == never unregister");
+
+static int drm_dp_cec_adap_enable(struct cec_adapter *adap, bool enable)
+{
+	struct drm_dp_aux *aux = cec_get_drvdata(adap);
+	u32 val = enable ? DP_CEC_TUNNELING_ENABLE : 0;
+	ssize_t err = 0;
+
+	err = drm_dp_dpcd_writeb(aux, DP_CEC_TUNNELING_CONTROL, val);
+	return (enable && err < 0) ? err : 0;
+}
+
+static int drm_dp_cec_adap_log_addr(struct cec_adapter *adap, u8 addr)
+{
+	struct drm_dp_aux *aux = cec_get_drvdata(adap);
+	/* Bit 15 (logical address 15) should always be set */
+	u16 la_mask = 1 << CEC_LOG_ADDR_BROADCAST;
+	u8 mask[2];
+	ssize_t err;
+
+	if (addr != CEC_LOG_ADDR_INVALID)
+		la_mask |= adap->log_addrs.log_addr_mask | (1 << addr);
+	mask[0] = la_mask & 0xff;
+	mask[1] = la_mask >> 8;
+	err = drm_dp_dpcd_write(aux, DP_CEC_LOGICAL_ADDRESS_MASK, mask, 2);
+	return (addr != CEC_LOG_ADDR_INVALID && err < 0) ? err : 0;
+}
+
+static int drm_dp_cec_adap_transmit(struct cec_adapter *adap, u8 attempts,
+				    u32 signal_free_time, struct cec_msg *msg)
+{
+	struct drm_dp_aux *aux = cec_get_drvdata(adap);
+	unsigned int retries = min(5, attempts - 1);
+	ssize_t err;
+
+	err = drm_dp_dpcd_write(aux, DP_CEC_TX_MESSAGE_BUFFER,
+				msg->msg, msg->len);
+	if (err < 0)
+		return err;
+
+	err = drm_dp_dpcd_writeb(aux, DP_CEC_TX_MESSAGE_INFO,
+				 (msg->len - 1) | (retries << 4) |
+				 DP_CEC_TX_MESSAGE_SEND);
+	return err < 0 ? err : 0;
+}
+
+static int drm_dp_cec_adap_monitor_all_enable(struct cec_adapter *adap,
+					      bool enable)
+{
+	struct drm_dp_aux *aux = cec_get_drvdata(adap);
+	ssize_t err;
+	u8 val;
+
+	if (!(adap->capabilities & CEC_CAP_MONITOR_ALL))
+		return 0;
+
+	err = drm_dp_dpcd_readb(aux, DP_CEC_TUNNELING_CONTROL, &val);
+	if (err >= 0) {
+		if (enable)
+			val |= DP_CEC_SNOOPING_ENABLE;
+		else
+			val &= ~DP_CEC_SNOOPING_ENABLE;
+		err = drm_dp_dpcd_writeb(aux, DP_CEC_TUNNELING_CONTROL, val);
+	}
+	return (enable && err < 0) ? err : 0;
+}
+
+static void drm_dp_cec_adap_status(struct cec_adapter *adap,
+				   struct seq_file *file)
+{
+	struct drm_dp_aux *aux = cec_get_drvdata(adap);
+	struct drm_dp_desc desc;
+	struct drm_dp_dpcd_ident *id = &desc.ident;
+
+	if (drm_dp_read_desc(aux, &desc, true))
+		return;
+	seq_printf(file, "OUI: %*pdH\n",
+		   (int)sizeof(id->oui), id->oui);
+	seq_printf(file, "ID: %*pE\n",
+		   (int)strnlen(id->device_id, sizeof(id->device_id)),
+		   id->device_id);
+	seq_printf(file, "HW Rev: %d.%d\n", id->hw_rev >> 4, id->hw_rev & 0xf);
+	/*
+	 * Show this both in decimal and hex: at least one vendor
+	 * always reports this in hex.
+	 */
+	seq_printf(file, "FW/SW Rev: %d.%d (0x%02x.0x%02x)\n",
+		   id->sw_major_rev, id->sw_minor_rev,
+		   id->sw_major_rev, id->sw_minor_rev);
+}
+
+static const struct cec_adap_ops drm_dp_cec_adap_ops = {
+	.adap_enable = drm_dp_cec_adap_enable,
+	.adap_log_addr = drm_dp_cec_adap_log_addr,
+	.adap_transmit = drm_dp_cec_adap_transmit,
+	.adap_monitor_all_enable = drm_dp_cec_adap_monitor_all_enable,
+	.adap_status = drm_dp_cec_adap_status,
+};
+
+static int drm_dp_cec_received(struct drm_dp_aux *aux)
+{
+	struct cec_adapter *adap = aux->cec_adap;
+	struct cec_msg msg;
+	u8 rx_msg_info;
+	ssize_t err;
+
+	err = drm_dp_dpcd_readb(aux, DP_CEC_RX_MESSAGE_INFO, &rx_msg_info);
+	if (err < 0)
+		return err;
+
+	if (!(rx_msg_info & DP_CEC_RX_MESSAGE_ENDED))
+		return 0;
+
+	msg.len = (rx_msg_info & DP_CEC_RX_MESSAGE_LEN_MASK) + 1;
+	err = drm_dp_dpcd_read(aux, DP_CEC_RX_MESSAGE_BUFFER, msg.msg, msg.len);
+	if (err < 0)
+		return err;
+
+	cec_received_msg(adap, &msg);
+	return 0;
+}
+
+static void drm_dp_cec_handle_irq(struct drm_dp_aux *aux)
+{
+	struct cec_adapter *adap = aux->cec_adap;
+	u8 flags;
+
+	if (drm_dp_dpcd_readb(aux, DP_CEC_TUNNELING_IRQ_FLAGS, &flags) < 0)
+		return;
+
+	if (flags & DP_CEC_RX_MESSAGE_INFO_VALID)
+		drm_dp_cec_received(aux);
+
+	if (flags & DP_CEC_TX_MESSAGE_SENT)
+		cec_transmit_attempt_done(adap, CEC_TX_STATUS_OK);
+	else if (flags & DP_CEC_TX_LINE_ERROR)
+		cec_transmit_attempt_done(adap, CEC_TX_STATUS_ERROR |
+						CEC_TX_STATUS_MAX_RETRIES);
+	else if (flags &
+		 (DP_CEC_TX_ADDRESS_NACK_ERROR | DP_CEC_TX_DATA_NACK_ERROR))
+		cec_transmit_attempt_done(adap, CEC_TX_STATUS_NACK |
+						CEC_TX_STATUS_MAX_RETRIES);
+	drm_dp_dpcd_writeb(aux, DP_CEC_TUNNELING_IRQ_FLAGS, flags);
+}
+
+/**
+ * drm_dp_cec_irq() - handle CEC interrupt, if any
+ * @aux: DisplayPort AUX channel
+ *
+ * Should be called when handling an IRQ_HPD request. If CEC-tunneling-over-AUX
+ * is present, then it will check for a CEC_IRQ and handle it accordingly.
+ */
+void drm_dp_cec_irq(struct drm_dp_aux *aux)
+{
+	u8 cec_irq;
+	int ret;
+
+	mutex_lock(&aux->cec_mutex);
+	if (!aux->cec_adap)
+		goto unlock;
+
+	ret = drm_dp_dpcd_readb(aux, DP_DEVICE_SERVICE_IRQ_VECTOR_ESI1,
+				&cec_irq);
+	if (ret < 0 || !(cec_irq & DP_CEC_IRQ))
+		goto unlock;
+
+	drm_dp_cec_handle_irq(aux);
+	drm_dp_dpcd_writeb(aux, DP_DEVICE_SERVICE_IRQ_VECTOR_ESI1, DP_CEC_IRQ);
+unlock:
+	mutex_unlock(&aux->cec_mutex);
+}
+EXPORT_SYMBOL(drm_dp_cec_irq);
+
+static bool drm_dp_cec_cap(struct drm_dp_aux *aux, u8 *cec_cap)
+{
+	u8 cap = 0;
+
+	if (drm_dp_dpcd_readb(aux, DP_CEC_TUNNELING_CAPABILITY, &cap) != 1 ||
+	    !(cap & DP_CEC_TUNNELING_CAPABLE))
+		return false;
+	if (cec_cap)
+		*cec_cap = cap;
+	return true;
+}
+
+/*
+ * Called if the HPD was low for more than drm_dp_cec_unregister_delay
+ * seconds. This unregisters the CEC adapter.
+ */
+static void drm_dp_cec_unregister_work(struct work_struct *work)
+{
+	struct drm_dp_aux *aux = container_of(work, struct drm_dp_aux,
+					      cec_unregister_work.work);
+
+	if (!aux->cec_adap)
+		return;
+	mutex_lock(&aux->cec_mutex);
+	cec_unregister_adapter(aux->cec_adap);
+	aux->cec_adap = NULL;
+	mutex_unlock(&aux->cec_mutex);
+}
+
+/*
+ * A new EDID is set. If there is no CEC adapter, then create one. If
+ * there was a CEC adapter, then check if the CEC adapter properties
+ * were unchanged and just update the CEC physical address. Otherwise
+ * unregister the old CEC adapter and create a new one.
+ */
+void drm_dp_cec_set_edid(struct drm_dp_aux *aux, struct edid *edid)
+{
+	u32 cec_caps = CEC_CAP_DEFAULTS | CEC_CAP_NEEDS_HPD;
+	unsigned int num_las = 1;
+	u8 cap;
+
+#ifndef CONFIG_MEDIA_CEC_RC
+	/*
+	 * CEC_CAP_RC is part of CEC_CAP_DEFAULTS, but it is stripped by
+	 * cec_allocate_adapter() if CONFIG_MEDIA_CEC_RC is undefined.
+	 *
+	 * Do this here as well to ensure the tests against cec_caps are
+	 * correct.
+	 */
+	cec_caps &= ~CEC_CAP_RC;
+#endif
+	cancel_delayed_work_sync(&aux->cec_unregister_work);
+
+	mutex_lock(&aux->cec_mutex);
+	if (!drm_dp_cec_cap(aux, &cap)) {
+		/* CEC is not supported, unregister any existing adapter */
+		cec_unregister_adapter(aux->cec_adap);
+		aux->cec_adap = NULL;
+		goto unlock;
+	}
+
+	if (cap & DP_CEC_SNOOPING_CAPABLE)
+		cec_caps |= CEC_CAP_MONITOR_ALL;
+	if (cap & DP_CEC_MULTIPLE_LA_CAPABLE)
+		num_las = CEC_MAX_LOG_ADDRS;
+
+	if (aux->cec_adap) {
+		if (aux->cec_adap->capabilities == cec_caps &&
+		    aux->cec_adap->available_log_addrs == num_las) {
+			/* Unchanged, so just set the phys addr */
+			cec_s_phys_addr_from_edid(aux->cec_adap, edid);
+			goto unlock;
+		}
+		/*
+		 * The capabilities changed, so unregister the old
+		 * adapter first.
+		 */
+		cec_unregister_adapter(aux->cec_adap);
+	}
+
+	/* Create a new adapter */
+	aux->cec_adap = cec_allocate_adapter(&drm_dp_cec_adap_ops,
+					     aux, aux->cec_name, cec_caps,
+					     num_las);
+	if (IS_ERR(aux->cec_adap)) {
+		aux->cec_adap = NULL;
+		goto unlock;
+	}
+	if (cec_register_adapter(aux->cec_adap, aux->cec_parent)) {
+		cec_delete_adapter(aux->cec_adap);
+		aux->cec_adap = NULL;
+	} else {
+		/*
+		 * Update the phys addr for the new CEC adapter. When called
+		 * from drm_dp_cec_register_connector() edid == NULL, so in
+		 * that case the phys addr is just invalidated.
+		 */
+		cec_s_phys_addr_from_edid(aux->cec_adap, edid);
+	}
+unlock:
+	mutex_unlock(&aux->cec_mutex);
+}
+EXPORT_SYMBOL(drm_dp_cec_set_edid);
+
+/*
+ * The EDID disappeared (likely because of the HPD going down).
+ */
+void drm_dp_cec_unset_edid(struct drm_dp_aux *aux)
+{
+	mutex_lock(&aux->cec_mutex);
+	if (!aux->cec_adap)
+		goto unlock;
+	cec_phys_addr_invalidate(aux->cec_adap);
+	/*
+	 * We're done if we want to keep the CEC device
+	 * (drm_dp_cec_unregister_delay is 0) or if the DPCD still indicates
+	 * the CEC capability (expected for an integrated HDMI branch device).
+	 */
+	if (!drm_dp_cec_unregister_delay || drm_dp_cec_cap(aux, NULL))
+		goto unlock;
+
+	cancel_delayed_work_sync(&aux->cec_unregister_work);
+	if (aux->cec_adap) {
+		/* sanity check */
+		if (drm_dp_cec_unregister_delay > 600)
+			drm_dp_cec_unregister_delay = 600;
+		/*
+		 * Unregister the CEC adapter after drm_dp_cec_unregister_delay
+		 * seconds. This to debounce short HPD off-and-on cycles from
+		 * displays.
+		 */
+		schedule_delayed_work(&aux->cec_unregister_work,
+				      drm_dp_cec_unregister_delay * HZ);
+	}
+unlock:
+	mutex_unlock(&aux->cec_mutex);
+}
+EXPORT_SYMBOL(drm_dp_cec_unset_edid);
+
+/**
+ * drm_dp_cec_register_connector() - register a new connector
+ * @aux: DisplayPort AUX channel
+ * @name: name of the CEC device
+ * @parent: parent device
+ *
+ * A new connector was registered with associated CEC adapter name and
+ * CEC adapter parent device. After registering the name and parent
+ * drm_dp_cec_set_edid() is called to check if the connector supports
+ * CEC and to register a CEC adapter if that is the case.
+ */
+void drm_dp_cec_register_connector(struct drm_dp_aux *aux, const char *name,
+				struct device *parent)
+{
+	WARN_ON(aux->cec_adap);
+	aux->cec_name = name;
+	aux->cec_parent = parent;
+	INIT_DELAYED_WORK(&aux->cec_unregister_work, drm_dp_cec_unregister_work);
+
+	drm_dp_cec_set_edid(aux, NULL);
+}
+EXPORT_SYMBOL(drm_dp_cec_register_connector);
+
+/**
+ * drm_dp_cec_unregister_connector() - unregister the CEC adapter, if any
+ * @aux: DisplayPort AUX channel
+ */
+void drm_dp_cec_unregister_connector(struct drm_dp_aux *aux)
+{
+	if (!aux->cec_adap)
+		return;
+	cancel_delayed_work_sync(&aux->cec_unregister_work);
+	cec_unregister_adapter(aux->cec_adap);
+	aux->cec_adap = NULL;
+}
+EXPORT_SYMBOL(drm_dp_cec_unregister_connector);
diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index ffe14ec3e7f2..e6b0e08ee0aa 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -1073,6 +1073,7 @@  static void drm_dp_aux_crc_work(struct work_struct *work)
 void drm_dp_aux_init(struct drm_dp_aux *aux)
 {
 	mutex_init(&aux->hw_mutex);
+	mutex_init(&aux->cec_mutex);
 	INIT_WORK(&aux->crc_work, drm_dp_aux_crc_work);
 
 	aux->ddc.algo = &drm_dp_i2c_algo;
diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
index 62903bae0221..415ac52e8599 100644
--- a/include/drm/drm_dp_helper.h
+++ b/include/drm/drm_dp_helper.h
@@ -1062,6 +1062,9 @@  struct drm_dp_aux_msg {
 	size_t size;
 };
 
+struct cec_adapter;
+struct edid;
+
 /**
  * struct drm_dp_aux - DisplayPort AUX channel
  * @name: user-visible name of this AUX channel and the I2C-over-AUX adapter
@@ -1120,6 +1123,26 @@  struct drm_dp_aux {
 	 * @i2c_defer_count: Counts I2C DEFERs, used for DP validation.
 	 */
 	unsigned i2c_defer_count;
+	/**
+	 * @cec_mutex: mutex protecting the cec_ fields
+	 */
+	struct mutex cec_mutex;
+	/**
+	 * @cec_adap: the CEC adapter for CEC-Tunneling-over-AUX support.
+	 */
+	struct cec_adapter *cec_adap;
+	/**
+	 * @cec_name: name of the CEC adapter
+	 */
+	const char *cec_name;
+	/**
+	 * @cec_parent: parent device of the CEC adapter
+	 */
+	struct device *cec_parent;
+	/**
+	 * @cec_unregister_work: unregister the CEC adapter
+	 */
+	struct delayed_work cec_unregister_work;
 };
 
 ssize_t drm_dp_dpcd_read(struct drm_dp_aux *aux, unsigned int offset,
@@ -1242,4 +1265,37 @@  drm_dp_has_quirk(const struct drm_dp_desc *desc, enum drm_dp_quirk quirk)
 	return desc->quirks & BIT(quirk);
 }
 
+#ifdef CONFIG_DRM_DP_CEC
+void drm_dp_cec_irq(struct drm_dp_aux *aux);
+void drm_dp_cec_register_connector(struct drm_dp_aux *aux, const char *name,
+				 struct device *parent);
+void drm_dp_cec_unregister_connector(struct drm_dp_aux *aux);
+void drm_dp_cec_set_edid(struct drm_dp_aux *aux, struct edid *edid);
+void drm_dp_cec_unset_edid(struct drm_dp_aux *aux);
+#else
+static inline void drm_dp_cec_irq(struct drm_dp_aux *aux)
+{
+}
+
+static inline void drm_dp_cec_register_connector(struct drm_dp_aux *aux,
+					      const char *name,
+					      struct device *parent)
+{
+}
+
+static inline void drm_dp_cec_unregister_connector(struct drm_dp_aux *aux)
+{
+}
+
+static inline void drm_dp_cec_set_edid(struct drm_dp_aux *aux,
+				       struct edid *edid)
+{
+}
+
+static inline void drm_dp_cec_unset_edid(struct drm_dp_aux *aux)
+{
+}
+
+#endif
+
 #endif /* _DRM_DP_HELPER_H_ */

Comments

On Tue, Jun 12, 2018 at 01:18:29PM +0200, Hans Verkuil wrote:
> From: Hans Verkuil <hans.verkuil@cisco.com>
> 
> This adds support for the DisplayPort CEC-Tunneling-over-AUX
> feature that is part of the DisplayPort 1.3 standard.
> 
> Unfortunately, not all DisplayPort/USB-C to HDMI adapters with a
> chip that has this capability actually hook up the CEC pin, so
> even though a CEC device is created, it may not actually work.
> 
> Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
> ---
>  drivers/gpu/drm/Kconfig         |  10 +
>  drivers/gpu/drm/Makefile        |   1 +
>  drivers/gpu/drm/drm_dp_cec.c    | 423 ++++++++++++++++++++++++++++++++
>  drivers/gpu/drm/drm_dp_helper.c |   1 +
>  include/drm/drm_dp_helper.h     |  56 +++++
>  5 files changed, 491 insertions(+)
>  create mode 100644 drivers/gpu/drm/drm_dp_cec.c
> 
> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> index deeefa7a1773..d63876425cdc 100644
> --- a/drivers/gpu/drm/Kconfig
> +++ b/drivers/gpu/drm/Kconfig
> @@ -121,6 +121,16 @@ config DRM_LOAD_EDID_FIRMWARE
>  	  default case is N. Details and instructions how to build your own
>  	  EDID data are given in Documentation/EDID/HOWTO.txt.
>  
> +config DRM_DP_CEC
> +	bool "Enable DisplayPort CEC-Tunneling-over-AUX HDMI support"
> +	select CEC_CORE
> +	help
> +	  Choose this option if you want to enable HDMI CEC support for
> +	  DisplayPort/USB-C to HDMI adapters.
> +
> +	  Note: not all adapters support this feature, and even for those
> +	  that do support this they often do not hook up the CEC pin.
> +
>  config DRM_TTM
>  	tristate
>  	depends on DRM && MMU
> diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
> index 50093ff4479b..c787481c2502 100644
> --- a/drivers/gpu/drm/Makefile
> +++ b/drivers/gpu/drm/Makefile
> @@ -41,6 +41,7 @@ drm_kms_helper-$(CONFIG_DRM_PANEL_BRIDGE) += bridge/panel.o
>  drm_kms_helper-$(CONFIG_DRM_FBDEV_EMULATION) += drm_fb_helper.o
>  drm_kms_helper-$(CONFIG_DRM_KMS_CMA_HELPER) += drm_fb_cma_helper.o
>  drm_kms_helper-$(CONFIG_DRM_DP_AUX_CHARDEV) += drm_dp_aux_dev.o
> +drm_kms_helper-$(CONFIG_DRM_DP_CEC) += drm_dp_cec.o
>  
>  obj-$(CONFIG_DRM_KMS_HELPER) += drm_kms_helper.o
>  obj-$(CONFIG_DRM_DEBUG_MM_SELFTEST) += selftests/
> diff --git a/drivers/gpu/drm/drm_dp_cec.c b/drivers/gpu/drm/drm_dp_cec.c
> new file mode 100644
> index 000000000000..555a9fca3fef
> --- /dev/null
> +++ b/drivers/gpu/drm/drm_dp_cec.c
> @@ -0,0 +1,423 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * DisplayPort CEC-Tunneling-over-AUX support
> + *
> + * Copyright 2018 Cisco Systems, Inc. and/or its affiliates. All rights reserved.
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/slab.h>
> +#include <drm/drm_dp_helper.h>
> +#include <media/cec.h>
> +
> +/*
> + * Unfortunately it turns out that we have a chicken-and-egg situation
> + * here. Quite a few active (mini-)DP-to-HDMI or USB-C-to-HDMI adapters
> + * have a converter chip that supports CEC-Tunneling-over-AUX (usually the
> + * Parade PS176), but they do not wire up the CEC pin, thus making CEC
> + * useless.
> + *
> + * Sadly there is no way for this driver to know this. What happens is
> + * that a /dev/cecX device is created that is isolated and unable to see
> + * any of the other CEC devices. Quite literally the CEC wire is cut
> + * (or in this case, never connected in the first place).
> + *
> + * The reason so few adapters support this is that this tunneling protocol
> + * was never supported by any OS. So there was no easy way of testing it,
> + * and no incentive to correctly wire up the CEC pin.
> + *
> + * Hopefully by creating this driver it will be easier for vendors to
> + * finally fix their adapters and test the CEC functionality.
> + *
> + * I keep a list of known working adapters here:
> + *
> + * https://hverkuil.home.xs4all.nl/cec-status.txt
> + *
> + * Please mail me (hverkuil@xs4all.nl) if you find an adapter that works
> + * and is not yet listed there.
> + *
> + * Note that the current implementation does not support CEC over an MST hub.
> + * As far as I can see there is no mechanism defined in the DisplayPort
> + * standard to transport CEC interrupts over an MST device. It might be
> + * possible to do this through polling, but I have not been able to get that
> + * to work.
> + */
> +
> +/**
> + * DOC: dp cec helpers
> + *
> + * These functions take care of supporting the CEC-Tunneling-over-AUX
> + * feature of DisplayPort-to-HDMI adapters.
> + */
> +
> +/*
> + * When the EDID is unset because the HPD went low, then the CEC DPCD registers
> + * typically can no longer be read (true for a DP-to-HDMI adapter since it is
> + * powered by the HPD). However, some displays toggle the HPD off and on for a
> + * short period for one reason or another, and that would cause the CEC adapter
> + * to be removed and added again, even though nothing else changed.
> + *
> + * This module parameter sets a delay in seconds before the CEC adapter is
> + * actually unregistered. Only if the HPD does not return within that time will
> + * the CEC adapter be unregistered.

And whatever is trying to do cec is happy with the dpcd accesses
failing during that time?

> + *
> + * If it is set to 0, then the CEC adapter will never be unregistered for as
> + * long as the connector remains registered.
> + *
> + * Note that for integrated HDMI branch devices that support CEC the DPCD
> + * registers remain available even if the HPD goes low since it is not powered
> + * by the HPD. In that case the CEC adapter will never be unregistered during
> + * the life time of the connector. At least, this is the theory since I do not
> + * have hardware with an integrated HDMI branch device that supports CEC.
> + */
> +static unsigned int drm_dp_cec_unregister_delay = 1;
> +module_param(drm_dp_cec_unregister_delay, uint, 0600);
> +MODULE_PARM_DESC(drm_dp_cec_unregister_delay, "CEC unregister delay in seconds, 0 == never unregister");
> +
> +static int drm_dp_cec_adap_enable(struct cec_adapter *adap, bool enable)
> +{
> +	struct drm_dp_aux *aux = cec_get_drvdata(adap);
> +	u32 val = enable ? DP_CEC_TUNNELING_ENABLE : 0;
> +	ssize_t err = 0;
> +
> +	err = drm_dp_dpcd_writeb(aux, DP_CEC_TUNNELING_CONTROL, val);
> +	return (enable && err < 0) ? err : 0;
> +}
> +
> +static int drm_dp_cec_adap_log_addr(struct cec_adapter *adap, u8 addr)
> +I think I looked at the dpcd detais last time around. {
> +	struct drm_dp_aux *aux = cec_get_drvdata(adap);
> +	/* Bit 15 (logical address 15) should always be set */
> +	u16 la_mask = 1 << CEC_LOG_ADDR_BROADCAST;
> +	u8 mask[2];
> +	ssize_t err;
> +
> +	if (addr != CEC_LOG_ADDR_INVALID)
> +		la_mask |= adap->log_addrs.log_addr_mask | (1 << addr);
> +	mask[0] = la_mask & 0xff;
> +	mask[1] = la_mask >> 8;
> +	err = drm_dp_dpcd_write(aux, DP_CEC_LOGICAL_ADDRESS_MASK, mask, 2);
> +	return (addr != CEC_LOG_ADDR_INVALID && err < 0) ? err : 0;
> +}
> +
> +static int drm_dp_cec_adap_transmit(struct cec_adapter *adap, u8 attempts,
> +				    u32 signal_free_time, struct cec_msg *msg)

'msg' could be const perhaps?

> +{
> +	struct drm_dp_aux *aux = cec_get_drvdata(adap);
> +	unsigned int retries = min(5, attempts - 1);
> +	ssize_t err;
> +
> +	err = drm_dp_dpcd_write(aux, DP_CEC_TX_MESSAGE_BUFFER,
> +				msg->msg, msg->len);
> +	if (err < 0)
> +		return err;
> +
> +	err = drm_dp_dpcd_writeb(aux, DP_CEC_TX_MESSAGE_INFO,
> +				 (msg->len - 1) | (retries << 4) |
> +				 DP_CEC_TX_MESSAGE_SEND);
> +	return err < 0 ? err : 0;
> +}
> +
> +static int drm_dp_cec_adap_monitor_all_enable(struct cec_adapter *adap,
> +					      bool enable)
> +{
> +	struct drm_dp_aux *aux = cec_get_drvdata(adap);
> +	ssize_t err;
> +	u8 val;
> +
> +	if (!(adap->capabilities & CEC_CAP_MONITOR_ALL))
> +		return 0;
> +
> +	err = drm_dp_dpcd_readb(aux, DP_CEC_TUNNELING_CONTROL, &val);
> +	if (err >= 0) {
> +		if (enable)
> +			val |= DP_CEC_SNOOPING_ENABLE;
> +		else
> +			val &= ~DP_CEC_SNOOPING_ENABLE;
> +		err = drm_dp_dpcd_writeb(aux, DP_CEC_TUNNELING_CONTROL, val);
> +	}
> +	return (enable && err < 0) ? err : 0;
> +}
> +
> +static void drm_dp_cec_adap_status(struct cec_adapter *adap,
> +				   struct seq_file *file)
> +{
> +	struct drm_dp_aux *aux = cec_get_drvdata(adap);
> +	struct drm_dp_desc desc;
> +	struct drm_dp_dpcd_ident *id = &desc.ident;
> +
> +	if (drm_dp_read_desc(aux, &desc, true))
> +		return;
> +	seq_printf(file, "OUI: %*pdH\n",
> +		   (int)sizeof(id->oui), id->oui);
> +	seq_printf(file, "ID: %*pE\n",
> +		   (int)strnlen(id->device_id, sizeof(id->device_id)),
> +		   id->device_id);
> +	seq_printf(file, "HW Rev: %d.%d\n", id->hw_rev >> 4, id->hw_rev & 0xf);
> +	/*
> +	 * Show this both in decimal and hex: at least one vendor
> +	 * always reports this in hex.
> +	 */
> +	seq_printf(file, "FW/SW Rev: %d.%d (0x%02x.0x%02x)\n",
> +		   id->sw_major_rev, id->sw_minor_rev,
> +		   id->sw_major_rev, id->sw_minor_rev);
> +}
> +
> +static const struct cec_adap_ops drm_dp_cec_adap_ops = {
> +	.adap_enable = drm_dp_cec_adap_enable,
> +	.adap_log_addr = drm_dp_cec_adap_log_addr,
> +	.adap_transmit = drm_dp_cec_adap_transmit,
> +	.adap_monitor_all_enable = drm_dp_cec_adap_monitor_all_enable,
> +	.adap_status = drm_dp_cec_adap_status,
> +};
> +
> +static int drm_dp_cec_received(struct drm_dp_aux *aux)
> +{
> +	struct cec_adapter *adap = aux->cec_adap;
> +	struct cec_msg msg;
> +	u8 rx_msg_info;
> +	ssize_t err;
> +
> +	err = drm_dp_dpcd_readb(aux, DP_CEC_RX_MESSAGE_INFO, &rx_msg_info);
> +	if (err < 0)
> +		return err;
> +
> +	if (!(rx_msg_info & DP_CEC_RX_MESSAGE_ENDED))
> +		return 0;
> +
> +	msg.len = (rx_msg_info & DP_CEC_RX_MESSAGE_LEN_MASK) + 1;
> +	err = drm_dp_dpcd_read(aux, DP_CEC_RX_MESSAGE_BUFFER, msg.msg, msg.len);
> +	if (err < 0)
> +		return err;
> +
> +	cec_received_msg(adap, &msg);
> +	return 0;
> +}
> +
> +static void drm_dp_cec_handle_irq(struct drm_dp_aux *aux)
> +{
> +	struct cec_adapter *adap = aux->cec_adap;
> +	u8 flags;
> +
> +	if (drm_dp_dpcd_readb(aux, DP_CEC_TUNNELING_IRQ_FLAGS, &flags) < 0)
> +		return;
> +
> +	if (flags & DP_CEC_RX_MESSAGE_INFO_VALID)
> +		drm_dp_cec_received(aux);
> +
> +	if (flags & DP_CEC_TX_MESSAGE_SENT)
> +		cec_transmit_attempt_done(adap, CEC_TX_STATUS_OK);
> +	else if (flags & DP_CEC_TX_LINE_ERROR)
> +		cec_transmit_attempt_done(adap, CEC_TX_STATUS_ERROR |
> +						CEC_TX_STATUS_MAX_RETRIES);
> +	else if (flags &
> +		 (DP_CEC_TX_ADDRESS_NACK_ERROR | DP_CEC_TX_DATA_NACK_ERROR))
> +		cec_transmit_attempt_done(adap, CEC_TX_STATUS_NACK |
> +						CEC_TX_STATUS_MAX_RETRIES);
> +	drm_dp_dpcd_writeb(aux, DP_CEC_TUNNELING_IRQ_FLAGS, flags);
> +}
> +
> +/**
> + * drm_dp_cec_irq() - handle CEC interrupt, if any
> + * @aux: DisplayPort AUX channel
> + *
> + * Should be called when handling an IRQ_HPD request. If CEC-tunneling-over-AUX
> + * is present, then it will check for a CEC_IRQ and handle it accordingly.
> + */
> +void drm_dp_cec_irq(struct drm_dp_aux *aux)
> +{
> +	u8 cec_irq;
> +	int ret;
> +
> +	mutex_lock(&aux->cec_mutex);
> +	if (!aux->cec_adap)
> +		goto unlock;
> +
> +	ret = drm_dp_dpcd_readb(aux, DP_DEVICE_SERVICE_IRQ_VECTOR_ESI1,
> +				&cec_irq);
> +	if (ret < 0 || !(cec_irq & DP_CEC_IRQ))
> +		goto unlock;
> +
> +	drm_dp_cec_handle_irq(aux);
> +	drm_dp_dpcd_writeb(aux, DP_DEVICE_SERVICE_IRQ_VECTOR_ESI1, DP_CEC_IRQ);
> +unlock:
> +	mutex_unlock(&aux->cec_mutex);
> +}
> +EXPORT_SYMBOL(drm_dp_cec_irq);
> +
> +static bool drm_dp_cec_cap(struct drm_dp_aux *aux, u8 *cec_cap)
> +{
> +	u8 cap = 0;
> +
> +	if (drm_dp_dpcd_readb(aux, DP_CEC_TUNNELING_CAPABILITY, &cap) != 1 ||
> +	    !(cap & DP_CEC_TUNNELING_CAPABLE))
> +		return false;
> +	if (cec_cap)
> +		*cec_cap = cap;
> +	return true;
> +}
> +
> +/*
> + * Called if the HPD was low for more than drm_dp_cec_unregister_delay
> + * seconds. This unregisters the CEC adapter.
> + */
> +static void drm_dp_cec_unregister_work(struct work_struct *work)
> +{
> +	struct drm_dp_aux *aux = container_of(work, struct drm_dp_aux,
> +					      cec_unregister_work.work);
> +
> +	if (!aux->cec_adap)
> +		return;
> +	mutex_lock(&aux->cec_mutex);
> +	cec_unregister_adapter(aux->cec_adap);
> +	aux->cec_adap = NULL;
> +	mutex_unlock(&aux->cec_mutex);
> +}
> +
> +/*
> + * A new EDID is set. If there is no CEC adapter, then create one. If
> + * there was a CEC adapter, then check if the CEC adapter properties
> + * were unchanged and just update the CEC physical address. Otherwise
> + * unregister the old CEC adapter and create a new one.
> + */
> +void drm_dp_cec_set_edid(struct drm_dp_aux *aux, struct edid *edid)

'edid' can be const.

> +{
> +	u32 cec_caps = CEC_CAP_DEFAULTS | CEC_CAP_NEEDS_HPD;
> +	unsigned int num_las = 1;
> +	u8 cap;
> +
> +#ifndef CONFIG_MEDIA_CEC_RC
> +	/*
> +	 * CEC_CAP_RC is part of CEC_CAP_DEFAULTS, but it is stripped by
> +	 * cec_allocate_adapter() if CONFIG_MEDIA_CEC_RC is undefined.
> +	 *
> +	 * Do this here as well to ensure the tests against cec_caps are
> +	 * correct.
> +	 */
> +	cec_caps &= ~CEC_CAP_RC;
> +#endif
> +	cancel_delayed_work_sync(&aux->cec_unregister_work);
> +
> +	mutex_lock(&aux->cec_mutex);
> +	if (!drm_dp_cec_cap(aux, &cap)) {
> +		/* CEC is not supported, unregister any existing adapter */
> +		cec_unregister_adapter(aux->cec_adap);
> +		aux->cec_adap = NULL;
> +		goto unlock;
> +	}
> +
> +	if (cap & DP_CEC_SNOOPING_CAPABLE)
> +		cec_caps |= CEC_CAP_MONITOR_ALL;
> +	if (cap & DP_CEC_MULTIPLE_LA_CAPABLE)
> +		num_las = CEC_MAX_LOG_ADDRS;
> +
> +	if (aux->cec_adap) {
> +		if (aux->cec_adap->capabilities == cec_caps &&
> +		    aux->cec_adap->available_log_addrs == num_las) {
> +			/* Unchanged, so just set the phys addr */
> +			cec_s_phys_addr_from_edid(aux->cec_adap, edid);
> +			goto unlock;
> +		}
> +		/*
> +		 * The capabilities changed, so unregister the old
> +		 * adapter first.
> +		 */
> +		cec_unregister_adapter(aux->cec_adap);
> +	}
> +
> +	/* Create a new adapter */
> +	aux->cec_adap = cec_allocate_adapter(&drm_dp_cec_adap_ops,
> +					     aux, aux->cec_name, cec_caps,
> +					     num_las);
> +	if (IS_ERR(aux->cec_adap)) {
> +		aux->cec_adap = NULL;
> +		goto unlock;
> +	}
> +	if (cec_register_adapter(aux->cec_adap, aux->cec_parent)) {
> +		cec_delete_adapter(aux->cec_adap);
> +		aux->cec_adap = NULL;
> +	} else {
> +		/*
> +		 * Update the phys addr for the new CEC adapter. When called
> +		 * from drm_dp_cec_register_connector() edid == NULL, so in
> +		 * that case the phys addr is just invalidated.
> +		 */
> +		cec_s_phys_addr_from_edid(aux->cec_adap, edid);
> +	}
> +unlock:
> +	mutex_unlock(&aux->cec_mutex);
> +}
> +EXPORT_SYMBOL(drm_dp_cec_set_edid);
> +
> +/*
> + * The EDID disappeared (likely because of the HPD going down).
> + */
> +void drm_dp_cec_unset_edid(struct drm_dp_aux *aux)
> +{
> +	mutex_lock(&aux->cec_mutex);
> +	if (!aux->cec_adap)
> +		goto unlock;
> +	cec_phys_addr_invalidate(aux->cec_adap);
> +	/*
> +	 * We're done if we want to keep the CEC device
> +	 * (drm_dp_cec_unregister_delay is 0) or if the DPCD still indicates
> +	 * the CEC capability (expected for an integrated HDMI branch device).
> +	 */
> +	if (!drm_dp_cec_unregister_delay || drm_dp_cec_cap(aux, NULL))
> +		goto unlock;

The drm_dp_cec_unregister_delay semantics seem a bit unnatural to me.
I think ==0 -> no delay, <0 -> infinite delay would make more sense.
Although we already have the exact opposite with the vblank_offdelay for
some historical reason :(

> +
> +	cancel_delayed_work_sync(&aux->cec_unregister_work);

This looks like a potential deadlock to me.

> +	if (aux->cec_adap) {
> +		/* sanity check */
> +		if (drm_dp_cec_unregister_delay > 600)
> +			drm_dp_cec_unregister_delay = 600;
> +		/*
> +		 * Unregister the CEC adapter after drm_dp_cec_unregister_delay
> +		 * seconds. This to debounce short HPD off-and-on cycles from
> +		 * displays.
> +		 */
> +		schedule_delayed_work(&aux->cec_unregister_work,
> +				      drm_dp_cec_unregister_delay * HZ);
> +	}
> +unlock:
> +	mutex_unlock(&aux->cec_mutex);
> +}
> +EXPORT_SYMBOL(drm_dp_cec_unset_edid);
> +
> +/**
> + * drm_dp_cec_register_connector() - register a new connector
> + * @aux: DisplayPort AUX channel
> + * @name: name of the CEC device
> + * @parent: parent device
> + *
> + * A new connector was registered with associated CEC adapter name and
> + * CEC adapter parent device. After registering the name and parent
> + * drm_dp_cec_set_edid() is called to check if the connector supports
> + * CEC and to register a CEC adapter if that is the case.
> + */
> +void drm_dp_cec_register_connector(struct drm_dp_aux *aux, const char *name,
> +				struct device *parent)
> +{
> +	WARN_ON(aux->cec_adap);
> +	aux->cec_name = name;
> +	aux->cec_parent = parent;
> +	INIT_DELAYED_WORK(&aux->cec_unregister_work, drm_dp_cec_unregister_work);
> +
> +	drm_dp_cec_set_edid(aux, NULL);
> +}
> +EXPORT_SYMBOL(drm_dp_cec_register_connector);
> +
> +/**
> + * drm_dp_cec_unregister_connector() - unregister the CEC adapter, if any
> + * @aux: DisplayPort AUX channel
> + */
> +void drm_dp_cec_unregister_connector(struct drm_dp_aux *aux)
> +{
> +	if (!aux->cec_adap)
> +		return;
> +	cancel_delayed_work_sync(&aux->cec_unregister_work);
> +	cec_unregister_adapter(aux->cec_adap);
> +	aux->cec_adap = NULL;
> +}
> +EXPORT_SYMBOL(drm_dp_cec_unregister_connector);
> diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
> index ffe14ec3e7f2..e6b0e08ee0aa 100644
> --- a/drivers/gpu/drm/drm_dp_helper.c
> +++ b/drivers/gpu/drm/drm_dp_helper.c
> @@ -1073,6 +1073,7 @@ static void drm_dp_aux_crc_work(struct work_struct *work)
>  void drm_dp_aux_init(struct drm_dp_aux *aux)
>  {
>  	mutex_init(&aux->hw_mutex);
> +	mutex_init(&aux->cec_mutex);
>  	INIT_WORK(&aux->crc_work, drm_dp_aux_crc_work);
>  
>  	aux->ddc.algo = &drm_dp_i2c_algo;
> diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
> index 62903bae0221..415ac52e8599 100644
> --- a/include/drm/drm_dp_helper.h
> +++ b/include/drm/drm_dp_helper.h
> @@ -1062,6 +1062,9 @@ struct drm_dp_aux_msg {
>  	size_t size;
>  };
>  
> +struct cec_adapter;
> +struct edid;
> +
>  /**
>   * struct drm_dp_aux - DisplayPort AUX channel
>   * @name: user-visible name of this AUX channel and the I2C-over-AUX adapter
> @@ -1120,6 +1123,26 @@ struct drm_dp_aux {
>  	 * @i2c_defer_count: Counts I2C DEFERs, used for DP validation.
>  	 */
>  	unsigned i2c_defer_count;
> +	/**
> +	 * @cec_mutex: mutex protecting the cec_ fields
> +	 */
> +	struct mutex cec_mutex;
> +	/**
> +	 * @cec_adap: the CEC adapter for CEC-Tunneling-over-AUX support.
> +	 */
> +	struct cec_adapter *cec_adap;
> +	/**
> +	 * @cec_name: name of the CEC adapter
> +	 */
> +	const char *cec_name;
> +	/**
> +	 * @cec_parent: parent device of the CEC adapter
> +	 */
> +	struct device *cec_parent;
> +	/**
> +	 * @cec_unregister_work: unregister the CEC adapter
> +	 */
> +	struct delayed_work cec_unregister_work;

'struct { ... } cec;' could be a decent idea here.

I think I looked at the dpcd detais last time around so I'll not bother
this time around with that. Apart from the possible deadlock I think
this is looking pretty good.

>  };
>  
>  ssize_t drm_dp_dpcd_read(struct drm_dp_aux *aux, unsigned int offset,
> @@ -1242,4 +1265,37 @@ drm_dp_has_quirk(const struct drm_dp_desc *desc, enum drm_dp_quirk quirk)
>  	return desc->quirks & BIT(quirk);
>  }
>  
> +#ifdef CONFIG_DRM_DP_CEC
> +void drm_dp_cec_irq(struct drm_dp_aux *aux);
> +void drm_dp_cec_register_connector(struct drm_dp_aux *aux, const char *name,
> +				 struct device *parent);
> +void drm_dp_cec_unregister_connector(struct drm_dp_aux *aux);
> +void drm_dp_cec_set_edid(struct drm_dp_aux *aux, struct edid *edid);
> +void drm_dp_cec_unset_edid(struct drm_dp_aux *aux);
> +#else
> +static inline void drm_dp_cec_irq(struct drm_dp_aux *aux)
> +{
> +}
> +
> +static inline void drm_dp_cec_register_connector(struct drm_dp_aux *aux,
> +					      const char *name,
> +					      struct device *parent)
> +{
> +}
> +
> +static inline void drm_dp_cec_unregister_connector(struct drm_dp_aux *aux)
> +{
> +}
> +
> +static inline void drm_dp_cec_set_edid(struct drm_dp_aux *aux,
> +				       struct edid *edid)
> +{
> +}
> +
> +static inline void drm_dp_cec_unset_edid(struct drm_dp_aux *aux)
> +{
> +}
> +
> +#endif
> +
>  #endif /* _DRM_DP_HELPER_H_ */
> -- 
> 2.17.0
On 06/27/2018 07:57 PM, Ville Syrjälä wrote:
> On Tue, Jun 12, 2018 at 01:18:29PM +0200, Hans Verkuil wrote:
>> From: Hans Verkuil <hans.verkuil@cisco.com>
>>
>> This adds support for the DisplayPort CEC-Tunneling-over-AUX
>> feature that is part of the DisplayPort 1.3 standard.
>>
>> Unfortunately, not all DisplayPort/USB-C to HDMI adapters with a
>> chip that has this capability actually hook up the CEC pin, so
>> even though a CEC device is created, it may not actually work.
>>
>> Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
>> ---
>>  drivers/gpu/drm/Kconfig         |  10 +
>>  drivers/gpu/drm/Makefile        |   1 +
>>  drivers/gpu/drm/drm_dp_cec.c    | 423 ++++++++++++++++++++++++++++++++
>>  drivers/gpu/drm/drm_dp_helper.c |   1 +
>>  include/drm/drm_dp_helper.h     |  56 +++++
>>  5 files changed, 491 insertions(+)
>>  create mode 100644 drivers/gpu/drm/drm_dp_cec.c
>>

<snip>

>> +/*
>> + * When the EDID is unset because the HPD went low, then the CEC DPCD registers
>> + * typically can no longer be read (true for a DP-to-HDMI adapter since it is
>> + * powered by the HPD). However, some displays toggle the HPD off and on for a
>> + * short period for one reason or another, and that would cause the CEC adapter
>> + * to be removed and added again, even though nothing else changed.
>> + *
>> + * This module parameter sets a delay in seconds before the CEC adapter is
>> + * actually unregistered. Only if the HPD does not return within that time will
>> + * the CEC adapter be unregistered.
> 
> And whatever is trying to do cec is happy with the dpcd accesses
> failing during that time?

Correct. If there is no HPD, then the CEC adapter won't attempt to access dpcd.
And even if it does (e.g. if the HPD goes away in the middle of setting up a
transmit), that will just return an error.

> 
>> + *
>> + * If it is set to 0, then the CEC adapter will never be unregistered for as
>> + * long as the connector remains registered.
>> + *
>> + * Note that for integrated HDMI branch devices that support CEC the DPCD
>> + * registers remain available even if the HPD goes low since it is not powered
>> + * by the HPD. In that case the CEC adapter will never be unregistered during
>> + * the life time of the connector. At least, this is the theory since I do not
>> + * have hardware with an integrated HDMI branch device that supports CEC.
>> + */
>> +static unsigned int drm_dp_cec_unregister_delay = 1;
>> +module_param(drm_dp_cec_unregister_delay, uint, 0600);
>> +MODULE_PARM_DESC(drm_dp_cec_unregister_delay, "CEC unregister delay in seconds, 0 == never unregister");
>> +
>> +static int drm_dp_cec_adap_enable(struct cec_adapter *adap, bool enable)
>> +{
>> +	struct drm_dp_aux *aux = cec_get_drvdata(adap);
>> +	u32 val = enable ? DP_CEC_TUNNELING_ENABLE : 0;
>> +	ssize_t err = 0;
>> +
>> +	err = drm_dp_dpcd_writeb(aux, DP_CEC_TUNNELING_CONTROL, val);
>> +	return (enable && err < 0) ? err : 0;
>> +}
>> +
>> +static int drm_dp_cec_adap_log_addr(struct cec_adapter *adap, u8 addr)
>> +I think I looked at the dpcd detais last time around. {
>> +	struct drm_dp_aux *aux = cec_get_drvdata(adap);
>> +	/* Bit 15 (logical address 15) should always be set */
>> +	u16 la_mask = 1 << CEC_LOG_ADDR_BROADCAST;
>> +	u8 mask[2];
>> +	ssize_t err;
>> +
>> +	if (addr != CEC_LOG_ADDR_INVALID)
>> +		la_mask |= adap->log_addrs.log_addr_mask | (1 << addr);
>> +	mask[0] = la_mask & 0xff;
>> +	mask[1] = la_mask >> 8;
>> +	err = drm_dp_dpcd_write(aux, DP_CEC_LOGICAL_ADDRESS_MASK, mask, 2);
>> +	return (addr != CEC_LOG_ADDR_INVALID && err < 0) ? err : 0;
>> +}
>> +
>> +static int drm_dp_cec_adap_transmit(struct cec_adapter *adap, u8 attempts,
>> +				    u32 signal_free_time, struct cec_msg *msg)
> 
> 'msg' could be const perhaps?

No, this is a cec adapter callback, so I can't change the prototype unless I
change it for all CEC drivers. It should be const though, you are right about
that.

<snip>

>> +/*
>> + * A new EDID is set. If there is no CEC adapter, then create one. If
>> + * there was a CEC adapter, then check if the CEC adapter properties
>> + * were unchanged and just update the CEC physical address. Otherwise
>> + * unregister the old CEC adapter and create a new one.
>> + */
>> +void drm_dp_cec_set_edid(struct drm_dp_aux *aux, struct edid *edid)
> 
> 'edid' can be const.

Agreed.

<snip>

>> +/*
>> + * The EDID disappeared (likely because of the HPD going down).
>> + */
>> +void drm_dp_cec_unset_edid(struct drm_dp_aux *aux)
>> +{
>> +	mutex_lock(&aux->cec_mutex);
>> +	if (!aux->cec_adap)
>> +		goto unlock;
>> +	cec_phys_addr_invalidate(aux->cec_adap);
>> +	/*
>> +	 * We're done if we want to keep the CEC device
>> +	 * (drm_dp_cec_unregister_delay is 0) or if the DPCD still indicates
>> +	 * the CEC capability (expected for an integrated HDMI branch device).
>> +	 */
>> +	if (!drm_dp_cec_unregister_delay || drm_dp_cec_cap(aux, NULL))
>> +		goto unlock;
> 
> The drm_dp_cec_unregister_delay semantics seem a bit unnatural to me.
> I think ==0 -> no delay, <0 -> infinite delay would make more sense.
> Although we already have the exact opposite with the vblank_offdelay for
> some historical reason :(

I've changed it to:

0 = no delay
< 1000 = delay for that many seconds (default is 1)
>= 1000 = never unregister

> 
>> +
>> +	cancel_delayed_work_sync(&aux->cec_unregister_work);
> 
> This looks like a potential deadlock to me.

Yeah, fixed this.

> 
>> +	if (aux->cec_adap) {
>> +		/* sanity check */
>> +		if (drm_dp_cec_unregister_delay > 600)
>> +			drm_dp_cec_unregister_delay = 600;
>> +		/*
>> +		 * Unregister the CEC adapter after drm_dp_cec_unregister_delay
>> +		 * seconds. This to debounce short HPD off-and-on cycles from
>> +		 * displays.
>> +		 */
>> +		schedule_delayed_work(&aux->cec_unregister_work,
>> +				      drm_dp_cec_unregister_delay * HZ);
>> +	}
>> +unlock:
>> +	mutex_unlock(&aux->cec_mutex);
>> +}
>> +EXPORT_SYMBOL(drm_dp_cec_unset_edid);
>> @@ -1120,6 +1123,26 @@ struct drm_dp_aux {
>>  	 * @i2c_defer_count: Counts I2C DEFERs, used for DP validation.
>>  	 */
>>  	unsigned i2c_defer_count;
>> +	/**
>> +	 * @cec_mutex: mutex protecting the cec_ fields
>> +	 */
>> +	struct mutex cec_mutex;
>> +	/**
>> +	 * @cec_adap: the CEC adapter for CEC-Tunneling-over-AUX support.
>> +	 */
>> +	struct cec_adapter *cec_adap;
>> +	/**
>> +	 * @cec_name: name of the CEC adapter
>> +	 */
>> +	const char *cec_name;
>> +	/**
>> +	 * @cec_parent: parent device of the CEC adapter
>> +	 */
>> +	struct device *cec_parent;
>> +	/**
>> +	 * @cec_unregister_work: unregister the CEC adapter
>> +	 */
>> +	struct delayed_work cec_unregister_work;
> 
> 'struct { ... } cec;' could be a decent idea here.

I agree, changed this.

> 
> I think I looked at the dpcd detais last time around so I'll not bother
> this time around with that. Apart from the possible deadlock I think
> this is looking pretty good.

Thanks! I'll post a v7 with these changes.

Regards,

	Hans