[Intel-gfx] [PATCH v2 1/2] drm/i915/opregion: add support for mailbox #5 EDID

[Anisse Astier]

Le Tue, Jun 01, 2021 at 06:50:24PM +0300, Ville Syrj?l? a ?crit :
> On Mon, May 31, 2021 at 10:46:41PM +0200, Anisse Astier wrote:
> > The ACPI OpRegion Mailbox #5 ASLE extension may contain an EDID to be
> > used for the embedded display. Add support for using it via by adding
> > the EDID to the list of available modes on the connector, and use it for
> > eDP when available.
> > 
> > If a panel's EDID is broken, there may be an override EDID set in the
> > ACPI OpRegion mailbox #5. Use it if available.
> 
> Looks like Windows uses the ACPI _DDC method instead. We should probably
> do the same, just in case some crazy machine stores the EDID somewhere
> else.

Thanks, I wouldn't have thought of this. It seems Daniel Dadap did a
patch series to do just that, in a generic way:
https://lore.kernel.org/amd-gfx/20200727205357.27839-1-ddadap@nvidia.com/

I've tried patch 1 & 2, and after a fix[1] was able to call the _DDC method
on most devices, but without any EDID being returned.

I looked at the disassembled ACPI tables[2], and could not find any
device with the _DDC method. Are you sure it's the only method the
Windows driver uses to get the EDID ?

Regards,

Anisse

[1] _DOD ids should only use 16 lower bits, see table here:
https://uefi.org/specs/ACPI/6.4/Apx_B_Video_Extensions/display-specific-methods.html#dod-enumerate-all-devices-attached-to-the-display-adapter
[2] acpidump: https://gitlab.freedesktop.org/drm/intel/-/issues/3454#note_913970