[Intel-gfx] Fixing i915/opregion issues with firmware which lists more then 8 output devices

[Hans de Goede]

Hi,

On 06-11-15 11:19, Jani Nikula wrote:
> On Thu, 05 Nov 2015, Hans de Goede <hdegoede at redhat.com> wrote:
>> Hi,
>>
>> As discussed in the past, the i915 opregion code does not do the
>> right thing wrt the CADL field when there are more then 8 outputs,
>> this is causing issues on many different types of Asus laptops.
>>
>> This thread has details and a number of attempts to fix this:
>>
>> https://lkml.org/lkml/2014/2/11/1032
>>
>> This is impacting many users, here is an incomplete list of bug reports:
>>
>> https://bugzilla.kernel.org/show_bug.cgi?id=70241
>> https://bugzilla.kernel.org/show_bug.cgi?id=88941
>> https://bugzilla.redhat.com/show_bug.cgi?id=1144866
>> https://bugzilla.redhat.com/show_bug.cgi?id=1277785
>>
>> And I'm pretty sure that is just the tip of the iceberg, some users
>> have even analyzed their BIOS AML code and come up with an AML
>> hack in an attempt to fix this:
>>
>> http://blog.yjwong.name/fixing-display-backlight-hotkeys-on-asus-n550jk/
>>
>> It would be really great of someone from Intel could step up and start
>> working on a proper fix for this.
>
> Hans, thanks for bringing this up again.
>
> IIUC this would require something along the lines of:
>
> - Properly map acpi video bus children and DRM connectors in
>    intel_didl_outputs(). This is likely the hardest part. Save the
>    display ids in struct intel_connector.
>
> - Replace intel_setup_cadls() with functions to add/remove display ids
>    from opregion CADL.
>
> - Call the above functions as part of the modeset sequence (either from
>    intel_display.c or from the encoder hooks, whichever is best) to keep
>    CADL up-to-date about active outputs. Here, getting DP MST right is
>    probably the hard one.
>
> If the mapping goes wrong, and some id that used to be in CADL with the
> current code gets dropped, this may regress. That's the biggest risk,
> really.
>
> For the backlight/hotkey stuff, the minimal fix may be to keep the
> stupid static initialization of the CADL in intel_setup_cadls() like we
> have now, but ensuring the embedded displays are included in the list.

This is what Aaron's first attempt at fixing this more or less did:

https://lkml.org/lkml/2014/2/11/1032

Unless someone actually steps up to do a proper fix for this *now*,
maybe the i915 driver needs to incorporate a slightly revised / improved
version of that patch as a work around for now ?

Regards,

Hans