[2/2] drm: add fallback override/firmware EDID modes workaround

Submitted by Jani Nikula on June 7, 2019, 11:05 a.m.

Details

Message ID 20190607110513.12072-2-jani.nikula@intel.com
State New
Headers show
Series "Series without cover letter" ( rev: 1 ) in Intel GFX

Not browsing as part of any series.

Commit Message

Jani Nikula June 7, 2019, 11:05 a.m.
We've moved the override and firmware EDID (simply "override EDID" from
now on) handling to the low level drm_do_get_edid() function in order to
transparently use the override throughout the stack. The idea is that
you get the override EDID via the ->get_modes() hook.

Unfortunately, there are scenarios where the DDC probe in drm_get_edid()
called via ->get_modes() fails, although the preceding ->detect()
succeeds.

In the case reported by Paul Wise, the ->detect() hook,
intel_crt_detect(), relies on hotplug detect, bypassing the DDC. In the
case reported by Ilpo Järvinen, there is no ->detect() hook, which is
interpreted as connected. The subsequent DDC probe reached via
->get_modes() fails, and we don't even look at the override EDID,
resulting in no modes being added.

Because drm_get_edid() is used via ->detect() all over the place, we
can't trivially remove the DDC probe, as it leads to override EDID
effectively meaning connector forcing. The goal is that connector
forcing and override EDID remain orthogonal.

Generally, the underlying problem here is the conflation of ->detect()
and ->get_modes() via drm_get_edid(). The former should just detect, and
the latter should just get the modes, typically via reading the EDID. As
long as drm_get_edid() is used in ->detect(), it needs to retain the DDC
probe. Or such users need to have a separate DDC probe step first.

Work around the regression by falling back to a separate attempt at
getting the override EDID at drm_helper_probe_single_connector_modes()
level. With a working DDC and override EDID, it'll never be called; the
override EDID will come via ->get_modes(). There will still be a failing
DDC probe attempt in the cases that require the fallback.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107583
Reported-by: Paul Wise <pabs3@bonedaddy.net>
Cc: Paul Wise <pabs3@bonedaddy.net>
References: http://mid.mail-archive.com/alpine.DEB.2.20.1905262211270.24390@whs-18.cs.helsinki.fi
Reported-by: Ilpo Järvinen <ilpo.jarvinen@cs.helsinki.fi>
Cc: Ilpo Järvinen <ilpo.jarvinen@cs.helsinki.fi>
References: 15f080f08d48 ("drm/edid: respect connector force for drm_get_edid ddc probe")
Fixes: 53fd40a90f3c ("drm: handle override and firmware EDID at drm_do_get_edid() level")
Cc: <stable@vger.kernel.org> # v4.15+
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Harish Chegondi <harish.chegondi@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
---
 drivers/gpu/drm/drm_edid.c         | 29 +++++++++++++++++++++++++++++
 drivers/gpu/drm/drm_probe_helper.c |  7 +++++++
 include/drm/drm_edid.h             |  1 +
 3 files changed, 37 insertions(+)

Patch hide | download patch | download mbox

diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index c59a1e8c5ada..780146bfc225 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -1587,6 +1587,35 @@  static struct edid *drm_get_override_edid(struct drm_connector *connector)
 	return IS_ERR(override) ? NULL : override;
 }
 
+/**
+ * drm_add_override_edid_modes - add modes from override/firmware EDID
+ * @connector: connector we're probing
+ *
+ * Add modes from the override/firmware EDID, if available. Only to be used from
+ * drm_helper_probe_single_connector_modes() as a fallback for when DDC probe
+ * failed during drm_get_edid() and caused the override/firmware EDID to be
+ * skipped.
+ *
+ * Return: The number of modes added or 0 if we couldn't find any.
+ */
+int drm_add_override_edid_modes(struct drm_connector *connector)
+{
+	struct edid *override;
+	int num_modes = 0;
+
+	override = drm_get_override_edid(connector);
+	if (override) {
+		num_modes = drm_add_edid_modes(connector, override);
+		kfree(override);
+
+		DRM_DEBUG_KMS("[CONNECTOR:%d:%s] adding %d modes via fallback override/firmware EDID\n",
+			      connector->base.id, connector->name, num_modes);
+	}
+
+	return num_modes;
+}
+EXPORT_SYMBOL(drm_add_override_edid_modes);
+
 /**
  * drm_do_get_edid - get EDID data using a custom EDID block read function
  * @connector: connector we're probing
diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c
index 01e243f1ea94..ef2c468205a2 100644
--- a/drivers/gpu/drm/drm_probe_helper.c
+++ b/drivers/gpu/drm/drm_probe_helper.c
@@ -480,6 +480,13 @@  int drm_helper_probe_single_connector_modes(struct drm_connector *connector,
 
 	count = (*connector_funcs->get_modes)(connector);
 
+	/*
+	 * Fallback for when DDC probe failed in drm_get_edid() and thus skipped
+	 * override/firmware EDID.
+	 */
+	if (count == 0 && connector->status == connector_status_connected)
+		count = drm_add_override_edid_modes(connector);
+
 	if (count == 0 && connector->status == connector_status_connected)
 		count = drm_add_modes_noedid(connector, 1024, 768);
 	count += drm_helper_probe_add_cmdline_mode(connector);
diff --git a/include/drm/drm_edid.h b/include/drm/drm_edid.h
index 88b63801f9db..b9719418c3d2 100644
--- a/include/drm/drm_edid.h
+++ b/include/drm/drm_edid.h
@@ -478,6 +478,7 @@  struct edid *drm_get_edid_switcheroo(struct drm_connector *connector,
 				     struct i2c_adapter *adapter);
 struct edid *drm_edid_duplicate(const struct edid *edid);
 int drm_add_edid_modes(struct drm_connector *connector, struct edid *edid);
+int drm_add_override_edid_modes(struct drm_connector *connector);
 
 u8 drm_match_cea_mode(const struct drm_display_mode *to_match);
 enum hdmi_picture_aspect drm_get_cea_aspect_ratio(const u8 video_code);

Comments

On Fri, Jun 07, 2019 at 02:05:13PM +0300, Jani Nikula wrote:
> We've moved the override and firmware EDID (simply "override EDID" from
> now on) handling to the low level drm_do_get_edid() function in order to
> transparently use the override throughout the stack. The idea is that
> you get the override EDID via the ->get_modes() hook.
> 
> Unfortunately, there are scenarios where the DDC probe in drm_get_edid()
> called via ->get_modes() fails, although the preceding ->detect()
> succeeds.
> 
> In the case reported by Paul Wise, the ->detect() hook,
> intel_crt_detect(), relies on hotplug detect, bypassing the DDC. In the
> case reported by Ilpo Järvinen, there is no ->detect() hook, which is
> interpreted as connected. The subsequent DDC probe reached via
> ->get_modes() fails, and we don't even look at the override EDID,
> resulting in no modes being added.
> 
> Because drm_get_edid() is used via ->detect() all over the place, we
> can't trivially remove the DDC probe, as it leads to override EDID
> effectively meaning connector forcing. The goal is that connector
> forcing and override EDID remain orthogonal.
> 
> Generally, the underlying problem here is the conflation of ->detect()
> and ->get_modes() via drm_get_edid(). The former should just detect, and
> the latter should just get the modes, typically via reading the EDID. As
> long as drm_get_edid() is used in ->detect(), it needs to retain the DDC
> probe. Or such users need to have a separate DDC probe step first.
> 
> Work around the regression by falling back to a separate attempt at
> getting the override EDID at drm_helper_probe_single_connector_modes()
> level. With a working DDC and override EDID, it'll never be called; the
> override EDID will come via ->get_modes(). There will still be a failing
> DDC probe attempt in the cases that require the fallback.

I think we should also highlight here that EDID caching between ->detect
and ->get_modes is a further complicating concern, which is why making
drm_do_get_edid magically dtrt between ->detect and ->get_modes doesn't
work either.

Aside from that nit I think this covers our lengthy discussion completely.

> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107583
> Reported-by: Paul Wise <pabs3@bonedaddy.net>
> Cc: Paul Wise <pabs3@bonedaddy.net>
> References: http://mid.mail-archive.com/alpine.DEB.2.20.1905262211270.24390@whs-18.cs.helsinki.fi
> Reported-by: Ilpo Järvinen <ilpo.jarvinen@cs.helsinki.fi>
> Cc: Ilpo Järvinen <ilpo.jarvinen@cs.helsinki.fi>
> References: 15f080f08d48 ("drm/edid: respect connector force for drm_get_edid ddc probe")
> Fixes: 53fd40a90f3c ("drm: handle override and firmware EDID at drm_do_get_edid() level")
> Cc: <stable@vger.kernel.org> # v4.15+
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Cc: Harish Chegondi <harish.chegondi@intel.com>
> Signed-off-by: Jani Nikula <jani.nikula@intel.com>

As discussed on irc, we need tested-by here from the reporters since
there's way too many losing and frustrangingly few winning moves here.

With all that, on the series:

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

Thanks a lot for slogging through all this and pondering all the options
and implications!

Cheers, Daniel
> ---
>  drivers/gpu/drm/drm_edid.c         | 29 +++++++++++++++++++++++++++++
>  drivers/gpu/drm/drm_probe_helper.c |  7 +++++++
>  include/drm/drm_edid.h             |  1 +
>  3 files changed, 37 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index c59a1e8c5ada..780146bfc225 100644
> --- a/drivers/gpu/drm/drm_edid.c
> +++ b/drivers/gpu/drm/drm_edid.c
> @@ -1587,6 +1587,35 @@ static struct edid *drm_get_override_edid(struct drm_connector *connector)
>  	return IS_ERR(override) ? NULL : override;
>  }
>  
> +/**
> + * drm_add_override_edid_modes - add modes from override/firmware EDID
> + * @connector: connector we're probing
> + *
> + * Add modes from the override/firmware EDID, if available. Only to be used from
> + * drm_helper_probe_single_connector_modes() as a fallback for when DDC probe
> + * failed during drm_get_edid() and caused the override/firmware EDID to be
> + * skipped.
> + *
> + * Return: The number of modes added or 0 if we couldn't find any.
> + */
> +int drm_add_override_edid_modes(struct drm_connector *connector)
> +{
> +	struct edid *override;
> +	int num_modes = 0;
> +
> +	override = drm_get_override_edid(connector);
> +	if (override) {
> +		num_modes = drm_add_edid_modes(connector, override);
> +		kfree(override);
> +
> +		DRM_DEBUG_KMS("[CONNECTOR:%d:%s] adding %d modes via fallback override/firmware EDID\n",
> +			      connector->base.id, connector->name, num_modes);
> +	}
> +
> +	return num_modes;
> +}
> +EXPORT_SYMBOL(drm_add_override_edid_modes);
> +
>  /**
>   * drm_do_get_edid - get EDID data using a custom EDID block read function
>   * @connector: connector we're probing
> diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c
> index 01e243f1ea94..ef2c468205a2 100644
> --- a/drivers/gpu/drm/drm_probe_helper.c
> +++ b/drivers/gpu/drm/drm_probe_helper.c
> @@ -480,6 +480,13 @@ int drm_helper_probe_single_connector_modes(struct drm_connector *connector,
>  
>  	count = (*connector_funcs->get_modes)(connector);
>  
> +	/*
> +	 * Fallback for when DDC probe failed in drm_get_edid() and thus skipped
> +	 * override/firmware EDID.
> +	 */
> +	if (count == 0 && connector->status == connector_status_connected)
> +		count = drm_add_override_edid_modes(connector);
> +
>  	if (count == 0 && connector->status == connector_status_connected)
>  		count = drm_add_modes_noedid(connector, 1024, 768);
>  	count += drm_helper_probe_add_cmdline_mode(connector);
> diff --git a/include/drm/drm_edid.h b/include/drm/drm_edid.h
> index 88b63801f9db..b9719418c3d2 100644
> --- a/include/drm/drm_edid.h
> +++ b/include/drm/drm_edid.h
> @@ -478,6 +478,7 @@ struct edid *drm_get_edid_switcheroo(struct drm_connector *connector,
>  				     struct i2c_adapter *adapter);
>  struct edid *drm_edid_duplicate(const struct edid *edid);
>  int drm_add_edid_modes(struct drm_connector *connector, struct edid *edid);
> +int drm_add_override_edid_modes(struct drm_connector *connector);
>  
>  u8 drm_match_cea_mode(const struct drm_display_mode *to_match);
>  enum hdmi_picture_aspect drm_get_cea_aspect_ratio(const u8 video_code);
> -- 
> 2.20.1
>




On Sat, 08 Jun 2019, Paul Wise <pabs3@bonedaddy.net> wrote:
> On Sat, 2019-06-08 at 13:10 +0800, Paul Wise wrote:
>
>> I've tested these two patches on top of Linux v5.2-rc3 and the EDID
>> override works correctly on an Intel Ironlake GPU with a monitor that
>> lost its EDID a while ago.
>
> While testing I noticed a couple of things:
>
> While everything the GUI is the correct resolution, GNOME is unable to
> identify the monitor vendor or model. This is a regression from the
> previous edid override functionality. It looks like this is because the
> edid file in /sys is not populated with the EDID override data.

Right, I've added a call to drm_connector_update_edid_property() in v2
to address this issue.

> I got a crash due to null pointer dereference at one point, I'll try to
> track down when this happens.

Can't think of why this would happen; the backtrace might offer clues.

Thanks for testing!

BR,
Jani.