[PATCH] drm/i915/vlv: Add cdclk workaround for DSI

[Hans de Goede]

Hi,

On 19-12-17 20:48, Ville Syrjälä wrote:
> On Tue, Dec 19, 2017 at 08:31:07PM +0100, Hans de Goede wrote:
>> Hi,
>>
>> I forgot to add a coverletter, anyways what I wanted to put in the
>> coverletter and not in the commit message is a link to a picture of the
>> problem this fixes:
>>
>> https://fedorapeople.org/~jwrdegoede/IMG_20171217_195637.jpg
>>
>> Note the screen is actually a portrait screen, so the picture is the
>> right way up. Beside the obvious left shift with wrap-around of the
>> picture, also all the green in there is supposed to be blue.
>>
>> Another less clear picture is this one:
>>
>> https://fedorapeople.org/~jwrdegoede/IMG_20171217_195507.jpg
>>
>> Again with wrong colors.
>>
>> ###
>>
>> While working on this I also noticed that the pixelclock as
>> the driver gets it from the VBT is not the same as the one the
>> GOP uses, on the tablet in question the VBT says 77000 KHz
>> and the GOP uses (according to the initial readback) 78125 KHz,
>> on another tablet I noticed the VBT saying 78125 KHz, where
>> as the GOP was using 68xxx KHz which came to a refresh-rate
>> of around 60 Hz, where as the VBT value is 69 Hz IIRC.
>>
>> Neither of these cause any actual issue (fixing the pixelclock
>> to match the GOP programmed value does not fix the issue, where
>> as using the GOP cdclk of 333333KHz does).
> 
> https://patchwork.freedesktop.org/patch/127189/
> 
> I suppose it's unlike that would help here since it's just about the
> overlap in dual link mode, but there could be other fail in the DSI
> clock code.

Yes that is is not applicable to the Vi8 where I'm seeing the
77000 KHz used by GOP vs 78125 KHz used by i915.

Looking at intel_dsi_vbt_init the pclk on the boards where I'm
seeing an inconsistency is just taken directly from mode->clock,
which in turn is simply dvo_timing->clock * 10.

Again: these different pixel-clocks do not seem to be an issue,
I just noticed this too while looking at the problem best seen
here:

https://fedorapeople.org/~jwrdegoede/IMG_20171217_195637.jpg

Regards,

Hans