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

[Thomas Preston]

On 07/03/2019 10:34, Jani Nikula wrote:
> > > On Wed, 06 Mar 2019, Thomas Preston <thomas.preston@xxxxxxxxxxxxxxx> 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.
>
> In the long run you'll have better control of what your specific product
> does by using a VBT. However, I think we'll probably have to take the
> patch anyway.

Would you like me to resubmit with the suggested changes?

> > 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!
>
> There are dangers with default VBTs too. They might contain incorrect
> information about the specific board you have. You'll also have to set
> up the opregion, not just VBT.

I believe OpRegion is being set up correctly with ACPI tables, but ASLS=0
(points to OpRegion) is quite suspicious. I need to do more digging around
how our BIOS is set up.

> I'm afraid I can't help you there. You already know where to look to see
> how the kernel side expects things to work.
>
> For testing, the i915.vbt_firmware module parameter is helpful, so you
> don't need to change your BIOS to change the VBT.

That's great thanks, I will work on VBT using this for now.