[PATCH] drm/i915/ddi: Fix default eDP detection on port A

[Thomas Preston]

Hi,
Thanks for looking at this.

On 07/03/2019 08:18, Jani Nikula wrote:
> 
> The subject should probably have "drm/i915/bios" or "drm/i915/vbt".
> 

Noted

> On Wed, 06 Mar 2019, Thomas Preston <thomas.preston at codethink.co.uk> wrote:
>> We rely on VBT DDI port info for eDP detection on GEN9 platforms and
>> above. This breaks GEN9 platforms which don't have VBT because port A
>> eDP now defaults to false. Fix this by defaulting to true when VBT is
>> missing.
> 
> Please include more details about the machine that doesn't have VBT. Why
> don't you have VBT?
> 

We have upgraded from an earlier kernel version (an Intel BSP on v4.1)
which did not require VBT and so our BIOS isn't set up correctly. The
BIOS doesn't set ASLS and fails to find ACPI OpRegion:

[    9.368433] [drm:intel_opregion_setup [i915]] graphic opregion physical addr: 0x0
[    9.368490] [drm:intel_opregion_setup [i915]] ACPI OpRegion not supported!

So now our port A is DP instead of eDP. I was hoping a return to "default"
values would remedy this, but I think it's pretty clear now that we should
focus on fixing VBT.

I've found a default VBT in the BSP but not sure how to get it into BIOS.
If you could point me in the right direction here that would be really
useful!

> Personally I think it was a mistake originally to make guesses about the
> outputs in absence of VBT on DDI platforms, because we can never get the
> generic guesses right across all ports and all products. And for the
> record, that was the result of an easy choice to enable developers way
> back when, and forgotten.
> 
> Certainly eDP is more likely than something else on port A. But this
> will break any outlier products without VBT that have a non-eDP output
> on port A. I guess it's a risk we have to take, and handle the fallout
> later.
> 
> Acked-by: Jani Nikula <jani.nikula at intel.com>
> 
>> Fixes: commit a98d9c1d7e9b ("drm/i915/ddi: Rely on VBT DDI port info for eDP detection")
> 
> The Fixes: format does *not* include "commit" text.
> 

I got that from scripts/checkpatch.pl but noted, thanks.

Kind regards,
Tom