[PATCHv4,1/3] drm: add support for DisplayPort CEC-Tunneling-over-AUX

Submitted by Hans Verkuil on Sept. 16, 2017, 2:17 p.m.

Details

Message ID 20170916141726.4921-2-hverkuil@xs4all.nl
State New
Headers show
Series "drm/i915: add DisplayPort CEC-Tunneling-over-AUX support" ( rev: 5 ) in DRI devel

Not browsing as part of any series.

Commit Message

Hans Verkuil Sept. 16, 2017, 2:17 p.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>
Tested-by: Carlos Santa <carlos.santa@intel.com>
---
 drivers/gpu/drm/Kconfig      |  10 ++
 drivers/gpu/drm/Makefile     |   1 +
 drivers/gpu/drm/drm_dp_cec.c | 292 +++++++++++++++++++++++++++++++++++++++++++
 include/drm/drm_dp_helper.h  |  24 ++++
 4 files changed, 327 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 83cb2a88c204..1f2708df5c4e 100644
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -120,6 +120,16 @@  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 24a066e1841c..c6552c62049e 100644
--- a/drivers/gpu/drm/Makefile
+++ b/drivers/gpu/drm/Makefile
@@ -40,6 +40,7 @@  drm_kms_helper-$(CONFIG_DRM_LOAD_EDID_FIRMWARE) += drm_edid_load.o
 drm_kms_helper-$(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..d110cac007de
--- /dev/null
+++ b/drivers/gpu/drm/drm_dp_cec.c
@@ -0,0 +1,292 @@ 
+/*
+ * DisplayPort CEC-Tunneling-over-AUX support
+ *
+ * Copyright 2017 Cisco Systems, Inc. and/or its affiliates. All rights reserved.
+ *
+ * This program is free software; you may redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; version 2 of the License.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#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).
+ *
+ * I suspect that 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.
+ */
+
+/**
+ * DOC: dp cec helpers
+ *
+ * These functions take care of supporting the CEC-Tunneling-over-AUX
+ * feature of DisplayPort-to-HDMI adapters.
+ */
+
+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: %02x-%02x-%02x\n",
+		   id->oui[0], id->oui[1], id->oui[2]);
+	seq_printf(file, "ID: %.*s\n",
+		   (int)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 bool 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 false;
+
+	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);
+	return true;
+}
+
+/**
+ * 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.
+ *
+ * Returns true if an interrupt was handled successfully or false otherwise.
+ */
+bool drm_dp_cec_irq(struct drm_dp_aux *aux)
+{
+	bool handled;
+	u8 cec_irq;
+	int ret;
+
+	if (!aux->cec_adap)
+		return false;
+
+	ret = drm_dp_dpcd_readb(aux, DP_DEVICE_SERVICE_IRQ_VECTOR_ESI1,
+				&cec_irq);
+	if (ret < 0 || !(cec_irq & DP_CEC_IRQ))
+		return false;
+
+	handled = drm_dp_cec_handle_irq(aux);
+	drm_dp_dpcd_writeb(aux, DP_DEVICE_SERVICE_IRQ_VECTOR_ESI1, DP_CEC_IRQ);
+	return handled;
+}
+EXPORT_SYMBOL(drm_dp_cec_irq);
+
+/**
+ * drm_dp_cec_configure_adapter() - configure the CEC adapter
+ * @aux: DisplayPort AUX channel
+ * @name: name of the CEC device
+ * @parent: parent device
+ *
+ * Checks if this is a DisplayPort-to-HDMI adapter that supports
+ * CEC-tunneling-over-AUX, and if so it creates a CEC device.
+ *
+ * If a CEC device was already created, then check if the capabilities
+ * have changed. If not, then do nothing. Otherwise destroy the old
+ * CEC device and create a new CEC device.
+ *
+ * This can happen when one DP-to-HDMI adapter is disconnected and
+ * replaced by another adapter with different CEC capabilities.
+ *
+ * Returns 0 on success or a negative error code on failure.
+ */
+int drm_dp_cec_configure_adapter(struct drm_dp_aux *aux, const char *name,
+				 struct device *parent)
+{
+	u32 cec_caps = CEC_CAP_DEFAULTS | CEC_CAP_NEEDS_HPD;
+	unsigned int num_las = 1;
+	int err;
+	u8 cap;
+
+	if (drm_dp_dpcd_readb(aux, DP_CEC_TUNNELING_CAPABILITY, &cap) != 1 ||
+	    !(cap & DP_CEC_TUNNELING_CAPABLE)) {
+		cec_unregister_adapter(aux->cec_adap);
+		aux->cec_adap = NULL;
+		return -ENODEV;
+	}
+
+	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)
+			return 0;
+		cec_unregister_adapter(aux->cec_adap);
+	}
+
+	aux->cec_adap = cec_allocate_adapter(&drm_dp_cec_adap_ops,
+			 aux, name, cec_caps, num_las);
+	if (IS_ERR(aux->cec_adap)) {
+		err = PTR_ERR(aux->cec_adap);
+		aux->cec_adap = NULL;
+		return err;
+	}
+	err = cec_register_adapter(aux->cec_adap, parent);
+	if (err) {
+		cec_delete_adapter(aux->cec_adap);
+		aux->cec_adap = NULL;
+	}
+	return err;
+}
+EXPORT_SYMBOL(drm_dp_cec_configure_adapter);
diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
index b17476a6909c..0e236dd40b42 100644
--- a/include/drm/drm_dp_helper.h
+++ b/include/drm/drm_dp_helper.h
@@ -952,6 +952,8 @@  struct drm_dp_aux_msg {
 	size_t size;
 };
 
+struct cec_adapter;
+
 /**
  * struct drm_dp_aux - DisplayPort AUX channel
  * @name: user-visible name of this AUX channel and the I2C-over-AUX adapter
@@ -1010,6 +1012,10 @@  struct drm_dp_aux {
 	 * @i2c_defer_count: Counts I2C DEFERs, used for DP validation.
 	 */
 	unsigned i2c_defer_count;
+	/**
+	 * @cec_adap: the CEC adapter for CEC-Tunneling-over-AUX support.
+	 */
+	struct cec_adapter *cec_adap;
 };
 
 ssize_t drm_dp_dpcd_read(struct drm_dp_aux *aux, unsigned int offset,
@@ -1132,4 +1138,22 @@  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
+bool drm_dp_cec_irq(struct drm_dp_aux *aux);
+int drm_dp_cec_configure_adapter(struct drm_dp_aux *aux, const char *name,
+				 struct device *parent);
+#else
+static inline bool drm_dp_cec_irq(struct drm_dp_aux *aux)
+{
+	return false;
+}
+
+static inline int drm_dp_cec_configure_adapter(struct drm_dp_aux *aux,
+					       const char *name,
+					       struct device *parent)
+{
+	return -ENODEV;
+}
+#endif
+
 #endif /* _DRM_DP_HELPER_H_ */

Comments

On Sat, Sep 16, 2017 at 04:17:24PM +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.
> 

FYI we prefer to put the changelog into the commit message. Makes it
easier to see which version of the patch we're dealing with, and avoids
having to open up some other mail when doing the review.

> Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
> Tested-by: Carlos Santa <carlos.santa@intel.com>
> ---
>  drivers/gpu/drm/Kconfig      |  10 ++
>  drivers/gpu/drm/Makefile     |   1 +
>  drivers/gpu/drm/drm_dp_cec.c | 292 +++++++++++++++++++++++++++++++++++++++++++
>  include/drm/drm_dp_helper.h  |  24 ++++
>  4 files changed, 327 insertions(+)
>  create mode 100644 drivers/gpu/drm/drm_dp_cec.c
> 
> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> index 83cb2a88c204..1f2708df5c4e 100644
> --- a/drivers/gpu/drm/Kconfig
> +++ b/drivers/gpu/drm/Kconfig
> @@ -120,6 +120,16 @@ 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 24a066e1841c..c6552c62049e 100644
> --- a/drivers/gpu/drm/Makefile
> +++ b/drivers/gpu/drm/Makefile
> @@ -40,6 +40,7 @@ drm_kms_helper-$(CONFIG_DRM_LOAD_EDID_FIRMWARE) += drm_edid_load.o
>  drm_kms_helper-$(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..d110cac007de
> --- /dev/null
> +++ b/drivers/gpu/drm/drm_dp_cec.c
> @@ -0,0 +1,292 @@
> +/*
> + * DisplayPort CEC-Tunneling-over-AUX support
> + *
> + * Copyright 2017 Cisco Systems, Inc. and/or its affiliates. All rights reserved.
> + *
> + * This program is free software; you may redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; version 2 of the License.
> + *
> + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
> + * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
> + * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
> + * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
> + * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
> + * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
> + * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
> + * SOFTWARE.
> + */
> +
> +#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).
> + *
> + * I suspect that 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.
> + */
> +
> +/**
> + * DOC: dp cec helpers
> + *
> + * These functions take care of supporting the CEC-Tunneling-over-AUX
> + * feature of DisplayPort-to-HDMI adapters.
> + */
> +
> +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: %02x-%02x-%02x\n",
> +		   id->oui[0], id->oui[1], id->oui[2]);

We use %*phD elsewhere

> +	seq_printf(file, "ID: %.*s\n",
> +		   (int)sizeof(id->device_id), id->device_id);

%*pE used elsewhere

> +	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 bool 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 false;
> +
> +	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);
> +	return true;
> +}
> +
> +/**
> + * 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.
> + *
> + * Returns true if an interrupt was handled successfully or false otherwise.
> + */
> +bool drm_dp_cec_irq(struct drm_dp_aux *aux)
> +{
> +	bool handled;
> +	u8 cec_irq;
> +	int ret;
> +
> +	if (!aux->cec_adap)
> +		return false;
> +
> +	ret = drm_dp_dpcd_readb(aux, DP_DEVICE_SERVICE_IRQ_VECTOR_ESI1,
> +				&cec_irq);
> +	if (ret < 0 || !(cec_irq & DP_CEC_IRQ))
> +		return false;
> +
> +	handled = drm_dp_cec_handle_irq(aux);
> +	drm_dp_dpcd_writeb(aux, DP_DEVICE_SERVICE_IRQ_VECTOR_ESI1, DP_CEC_IRQ);
> +	return handled;
> +}
> +EXPORT_SYMBOL(drm_dp_cec_irq);
> +
> +/**
> + * drm_dp_cec_configure_adapter() - configure the CEC adapter
> + * @aux: DisplayPort AUX channel
> + * @name: name of the CEC device
> + * @parent: parent device
> + *
> + * Checks if this is a DisplayPort-to-HDMI adapter that supports
> + * CEC-tunneling-over-AUX, and if so it creates a CEC device.
> + *
> + * If a CEC device was already created, then check if the capabilities
> + * have changed. If not, then do nothing. Otherwise destroy the old
> + * CEC device and create a new CEC device.
> + *
> + * This can happen when one DP-to-HDMI adapter is disconnected and
> + * replaced by another adapter with different CEC capabilities.
> + *
> + * Returns 0 on success or a negative error code on failure.
> + */
> +int drm_dp_cec_configure_adapter(struct drm_dp_aux *aux, const char *name,
> +				 struct device *parent)
> +{
> +	u32 cec_caps = CEC_CAP_DEFAULTS | CEC_CAP_NEEDS_HPD;
> +	unsigned int num_las = 1;
> +	int err;
> +	u8 cap;
> +
> +	if (drm_dp_dpcd_readb(aux, DP_CEC_TUNNELING_CAPABILITY, &cap) != 1 ||
> +	    !(cap & DP_CEC_TUNNELING_CAPABLE)) {
> +		cec_unregister_adapter(aux->cec_adap);
> +		aux->cec_adap = NULL;
> +		return -ENODEV;
> +	}
> +
> +	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)
> +			return 0;
> +		cec_unregister_adapter(aux->cec_adap);
> +	}
> +
> +	aux->cec_adap = cec_allocate_adapter(&drm_dp_cec_adap_ops,
> +			 aux, name, cec_caps, num_las);
> +	if (IS_ERR(aux->cec_adap)) {
> +		err = PTR_ERR(aux->cec_adap);
> +		aux->cec_adap = NULL;
> +		return err;
> +	}
> +	err = cec_register_adapter(aux->cec_adap, parent);

There's a bit of chicken and egg problem here. We should not register
any user visible interfaces until the full drm device has been set up.
There's a .late_register() hook for connectors for this purpose.

So I guess what we want to do is defer this registration until that
time, unless the connector is already registered. drm_dp_aux_register()
might be the right spot for this call, or maybe we want to put it next
to that call in driver code? Not sure.

Hmm. And I guess that's going to be somewhat racy unless we protect
the direct registration with connector->mutex. I hope that can't
deadlock...

> +	if (err) {
> +		cec_delete_adapter(aux->cec_adap);
> +		aux->cec_adap = NULL;
> +	}
> +	return err;
> +}
> +EXPORT_SYMBOL(drm_dp_cec_configure_adapter);
> diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
> index b17476a6909c..0e236dd40b42 100644
> --- a/include/drm/drm_dp_helper.h
> +++ b/include/drm/drm_dp_helper.h
> @@ -952,6 +952,8 @@ struct drm_dp_aux_msg {
>  	size_t size;
>  };
>  
> +struct cec_adapter;
> +
>  /**
>   * struct drm_dp_aux - DisplayPort AUX channel
>   * @name: user-visible name of this AUX channel and the I2C-over-AUX adapter
> @@ -1010,6 +1012,10 @@ struct drm_dp_aux {
>  	 * @i2c_defer_count: Counts I2C DEFERs, used for DP validation.
>  	 */
>  	unsigned i2c_defer_count;
> +	/**
> +	 * @cec_adap: the CEC adapter for CEC-Tunneling-over-AUX support.
> +	 */
> +	struct cec_adapter *cec_adap;
>  };
>  
>  ssize_t drm_dp_dpcd_read(struct drm_dp_aux *aux, unsigned int offset,
> @@ -1132,4 +1138,22 @@ 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
> +bool drm_dp_cec_irq(struct drm_dp_aux *aux);
> +int drm_dp_cec_configure_adapter(struct drm_dp_aux *aux, const char *name,
> +				 struct device *parent);
> +#else
> +static inline bool drm_dp_cec_irq(struct drm_dp_aux *aux)
> +{
> +	return false;
> +}
> +
> +static inline int drm_dp_cec_configure_adapter(struct drm_dp_aux *aux,
> +					       const char *name,
> +					       struct device *parent)
> +{
> +	return -ENODEV;
> +}
> +#endif
> +
>  #endif /* _DRM_DP_HELPER_H_ */
> -- 
> 2.14.1