On 06/14/2016 01:05 PM, Daniel Vetter wrote:
On Thu, May 26, 2016 at 4:39 PM, Mario Kleiner mario.kleiner.de@gmail.com wrote:
This reverts commit 013dd9e03872 ("drm/i915/dp: fall back to 18 bpp when sink capability is unknown")
This commit introduced a regression into stable kernels, as it reduces output color depth to 6 bpc for any video sink connected to a Displayport connector if that sink doesn't report a specific color depth via EDID, or if our EDID parser doesn't actually recognize the proper bpc from EDID.
Affected are active DisplayPort->VGA converters and active DisplayPort->DVI converters. Both should be able to handle 8 bpc, but are degraded to 6 bpc with this patch.
The reverted commit was meant to fix Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=105331
A followup patch implements a fix for that specific bug, which is caused by a faulty EDID of the affected DP panel by adding a new EDID quirk for that panel.
DP 18 bpp fallback handling and other improvements to DP sink bpc detection will be handled for future kernels in a separate series of patches.
Please backport to stable.
Signed-off-by: Mario Kleiner mario.kleiner.de@gmail.com Acked-by: Jani Nikula jani.nikula@intel.com Cc: stable@vger.kernel.org Cc: Ville Syrjälä ville.syrjala@linux.intel.com Cc: Daniel Vetter daniel.vetter@ffwll.ch
I wonder whether we shouldn't just move this into the DP code, and instead of looking at the edid (which is just pass-through for dp->vga dongles) we should only look at dpcd values? Or maybe only look at the edid value if the sink is native DP, and not when it's a dongle.
That would probably also avoid the quirk, and that quirk seems a bit fishy. -Daniel
This patch is just a simple fix for the color depth regression which affects stable kernels. It can be back-ported easily to affected stable kernels, as Jani advised me.
I wanted to clean up and resubmit that DP helper function which looks at dpcd values and might be a bit too much for stable, once this fix is in.
-mario