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

[Jani Nikula]

On Sun, 26 May 2019, Ilpo Järvinen <ilpo.jarvinen at cs.helsinki.fi> 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).

This should be fixed by commit

commit 48eaeb7664c76139438724d520a1ea4a84a3ed92
Author: Jani Nikula <jani.nikula at intel.com>
Date:   Mon Jun 10 12:30:54 2019 +0300

    drm: add fallback override/firmware EDID modes workaround

in drm-misc-fixes, cc: stable v4.15.

Thanks for the report.

BR,
Jani.


-- 
Jani Nikula, Intel Open Source Graphics Center