DRM/AST regression (likely 4.14 -> 4.19+), providing EDID manually fails

[Jani Nikula]

On Wed, 29 May 2019, Ilpo Järvinen <ilpo.jarvinen at cs.helsinki.fi> wrote:
> On Tue, 28 May 2019, Jani Nikula wrote:
>
>> On Mon, 27 May 2019, Ashutosh Dixit <ashutosh.dixit at intel.com> wrote:
>> > On Sun, 26 May 2019 12:50:51 -0700, Ilpo Järvinen wrote:
>> >>
>> >> Hi all,
>> >>
>> >> I've a workstation which has internal VGA that is detected as AST 2400 and
>> >> with it EDID has been always quite flaky (except for some time it worked
>> >> with 4.14 long enough that I thought the problems would be past until the
>> >> problems reappeared also with 4.14). Thus, I've provided manually the EDID
>> >> that I extracted from the monitor using other computer (the monitor itself
>> >> worked just fine on the earlier computer so it is likely fine).
>> >>
>> >> I setup the manual EDID using drm_kms_helper.edid_firmware, however,
>> >> after upgrading to 4.19.45 it stopped working (no "Got external EDID base
>> >> block" appears in dmesg, the text mode is kept in the lower res mode, and
>> >> Xorg logs no longer dumps the EDID info like it did with 4.14). So I guess
>> >> the EDID I provided manually on the command line is not correctly put into
>> >> use with 4.19+ kernels.
>> >>
>> >> The 4.19 dmesg indicated that drm_kms_helper.edid_firmware is deprecated
>> >> so I also tested with drm.edid_firmware it suggested as the replacement
>> >> but with no luck (but I believe also the drm_kms_helper one should have
>> >> worked as it was only "deprecated").
>> >>
>> >> I also tried 5.1.2 but it did not work any better (and with it also tried
>> >> removing all the manual *.edid_firmware from the command line so I still
>> >> need to provide one manually to have it reliable working it seems).
>> >
>> > I believe there is a bug already tracking this, here:
>> >
>> > https://bugs.freedesktop.org/show_bug.cgi?id=107583
>> 
>> Ilpo, does video=VGA-1:e command-line option work around the problem for
>> you?
>
> Yes it does; together with the modeline stuff for Xorg (after reading the 
> referenced bug report I realized I can fix the X side with it). So I now 
> have the desired modes/resolutions in use. Thank you all!

Great! It should be enough to just have the replacement firmware EDID
for the modes, as long as you have an EDID that represents the
capabilities of the display. The modelines for Xorg should not be
needed.

BR,
Jani.


-- 
Jani Nikula, Intel Open Source Graphics Center