Re: [PATCH 2/2] drm/edid: Add 6 bpc quirk for display AEO model 0.

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Thu, May 26, 2016 at 04:39:04PM +0200, Mario Kleiner wrote:
> Bugzilla https://bugzilla.kernel.org/show_bug.cgi?id=105331
> reports that the "AEO model 0" display is driven with 8 bpc
> without dithering by default, which looks bad because that
> panel is apparently a 6 bpc DP panel with faulty EDID.
> 
> A fix for this was made by commit 013dd9e03872
> ("drm/i915/dp: fall back to 18 bpp when sink capability is unknown").
> 
> That commit triggers new regressions in precision for DP->DVI and
> DP->VGA displays. A patch is out to revert that commit, but it will
> revert video output for the AEO model 0 panel to 8 bpc without
> dithering.
> 
> The EDID 1.3 of that panel, as decoded from the xrandr output
> attached to that bugzilla bug report, is somewhat faulty, and beyond
> other problems also sets the "DFP 1.x compliant TMDS" bit, which
> according to DFP spec means to drive the panel with 8 bpc and
> no dithering in absence of other colorimetry information.
> 
> Try to make the original bug reporter happy despite the
> faulty EDID by adding a quirk to mark that panel as 6 bpc,
> so 6 bpc output with dithering creates a nice picture.
> 
> Tested by injecting the edid from the fdo bug into a DP connector
> via drm_kms_helper.edid_firmware and verifying the 6 bpc + dithering
> is selected.
> 
> This patch should be backported to stable.
> 
> Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>
> Cc: stable@vger.kernel.org
> Cc: Jani Nikula <jani.nikula@intel.com>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>

Now I'm confused. I thought we didn't need any quirks?

> ---
>  drivers/gpu/drm/drm_edid.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index 7df26d4..2cb472b 100644
> --- a/drivers/gpu/drm/drm_edid.c
> +++ b/drivers/gpu/drm/drm_edid.c
> @@ -74,6 +74,8 @@
>  #define EDID_QUIRK_FORCE_8BPC			(1 << 8)
>  /* Force 12bpc */
>  #define EDID_QUIRK_FORCE_12BPC			(1 << 9)
> +/* Force 6bpc */
> +#define EDID_QUIRK_FORCE_6BPC			(1 << 10)
>  
>  struct detailed_mode_closure {
>  	struct drm_connector *connector;
> @@ -100,6 +102,9 @@ static struct edid_quirk {
>  	/* Unknown Acer */
>  	{ "ACR", 2423, EDID_QUIRK_FIRST_DETAILED_PREFERRED },
>  
> +	/* AEO model 0 reports 8 bpc, but is a 6 bpc panel */
> +	{ "AEO", 0, EDID_QUIRK_FORCE_6BPC },
> +
>  	/* Belinea 10 15 55 */
>  	{ "MAX", 1516, EDID_QUIRK_PREFER_LARGE_60 },
>  	{ "MAX", 0x77e, EDID_QUIRK_PREFER_LARGE_60 },
> @@ -4082,6 +4087,9 @@ int drm_add_edid_modes(struct drm_connector *connector, struct edid *edid)
>  
>  	drm_add_display_info(edid, &connector->display_info, connector);
>  
> +	if (quirks & EDID_QUIRK_FORCE_6BPC)
> +		connector->display_info.bpc = 6;
> +
>  	if (quirks & EDID_QUIRK_FORCE_8BPC)
>  		connector->display_info.bpc = 8;
>  
> -- 
> 2.7.0

-- 
Ville Syrjälä
Intel OTC
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