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