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

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Message-ID: <1bc46e12-5cee-e3d0-83db-2feee4fe5210@codethink.co.uk>
Date:   Thu, 7 Mar 2019 10:49:29 +0000
From:   Thomas Preston <thomas.preston@...ethink.co.uk>
To:     Jani Nikula <jani.nikula@...ux.intel.com>,
        joonas.lahtinen@...ux.intel.com, rodrigo.vivi@...el.com,
        airlied@...ux.ie, intel-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/i915/ddi: Fix default eDP detection on port A

On 07/03/2019 10:34, Jani Nikula wrote:
>>> On Wed, 06 Mar 2019, Thomas Preston <thomas.preston@...ethink.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.
> 
> 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.