[Intel-gfx] [PATCH] drm/i915/dp: force eDP lane count to max available lanes on BDW

[Dave Airlie]

On 14 July 2014 10:46, Dave Airlie <airlied at gmail.com> wrote:
> On 15 May 2014 18:58, Jani Nikula <jani.nikula at intel.com> wrote:
>> On Wed, 14 May 2014, Rodrigo Vivi <rodrigo.vivi at gmail.com> wrote:
>>> We do have to continue the investigation on the link training side, but
>>> since 76711 is a critical I'm completely in favor of this workaround for
>>> now.
>>>
>>> I just tested and it worked very well here, so:
>>>
>>> Tested-by: Rodrigo Vivi <rodrigo.vivi at gmail.com>
>>> Reviewed-by: Rodrigo Vivi <rodrigo.vivi at gmail.com>
>>
>> Pushed to -fixes, thanks for the review and testing.
>>
>> BR,
>> Jani.
>>
>>>
>>>
>>> On Wed, May 14, 2014 at 6:02 AM, Jani Nikula <jani.nikula at intel.com> wrote:
>>>
>>>> There are certain BDW high res eDP machines that regressed due to
>>>>
>>>> commit 38aecea0ccbb909d635619cba22f1891e589b434
>>>> Author: Daniel Vetter <daniel.vetter at ffwll.ch>
>>>> Date:   Mon Mar 3 11:18:10 2014 +0100
>>>>
>>>>     drm/i915: reverse dp link param selection, prefer fast over wide again
>>>>
>>>> The commit lead to 2 lanes at 5.4 Gbps being used instead of 4 lanes at
>>>> 2.7 Gbps on the affected machines. Link training succeeded for both, but
>>>> the screen remained blank with the former config. Further investigation
>>>> showed that 4 lanes at 5.4 Gbps worked also.
>>>>
>>>> The root cause for the blank screen using 2 lanes remains unknown, but
>>>> apparently the driver for a certain other operating system by default
>>>> uses the max available lanes. Follow suit on Broadwell eDP, for at least
>>>> until we figure out what is going on.
>
> Uggh, okay this lane thing is such a pita,
>
> On haswell the Lenovo dock in SST mode is broken by the original patch as well.
>
> I'm not sure we want to do IS_HASWELL here as well,
>
> I think we need to revert 38aecea0ccbb909d635619cba22f1891e589b434

Actually adding IS_HASWELL won't work since this problem is with a standard
DP port.

I'll send the reverts, though I've no idea if this another revert of a
revert etc.

Dave.