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

[Hans de Goede]

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).

Regards,

Hans



On 19-12-17 20:21, Hans de Goede wrote:
> At least on the Chuwi Vi8 (non pro/plus) the LCD panel will show an image
> shifted aprox. 20% to the left (with wraparound) and sometimes also wrong
> colors, showing that the panel controller is starting with sampling the
> datastream somewhere mid-line. This happens after the first blanking and
> re-init of the panel.
> 
> After looking at drm.debug output I noticed that initially we inherit the
> cdclk of 333333 KHz set by the GOP, but after the re-init we picked 266667
> KHz, which turns out to be the cause of this problem, a quick hack to hard
> code the cdclk to 333333 KHz makes the problem go away.
> 
> I've tested this on various Bay Trail devices:
> -Chuwi Vi8: 800x1280, 333333 at boot, requires 333333 to work properly
> -GP-electronic T701: 1024x600, 333333 at boot, works fine with 333333
> -PEAQ C1010: 1920x1200, 333333 at boot, works fine with 333333
> -PoV mobii-wintab-800w: 800x1280, 333333 at boot, works fine with 333333
> -Asus Transformer-T100TA: 1368x768, 320000 at boot, works fine with 320000
> 
> So it seems that the GOP is always using what vlv_calc_cdclk calls
> freq_320 as cdclk clock. Also note the comment in vlv_calc_cdclk about
> it avoiding 200 Mhz as clock because that causes issues in some cases.
> 
> This commit extends the "do not use 200 Mhz" workaround with an extra
> check to require atleast 320000 KHz (avoiding 266667 KHz) when a DSI
> panel is active.
> 
> Signed-off-by: Hans de Goede <hdegoede at redhat.com>
> ---
>   drivers/gpu/drm/i915/intel_cdclk.c | 8 ++++++++
>   1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/intel_cdclk.c b/drivers/gpu/drm/i915/intel_cdclk.c
> index 9c5ceb98d48f..cfb3f7fb3e1c 100644
> --- a/drivers/gpu/drm/i915/intel_cdclk.c
> +++ b/drivers/gpu/drm/i915/intel_cdclk.c
> @@ -1923,6 +1923,14 @@ int intel_crtc_compute_min_cdclk(const struct intel_crtc_state *crtc_state)
>   	if (crtc_state->has_audio && INTEL_GEN(dev_priv) >= 9)
>   		min_cdclk = max(2 * 96000, min_cdclk);
>   
> +	/*
> +	 * On Valleyview the GOP always uses 320000/333333 KHz if DSI is used,
> +	 * using a lower clock causes causes sync issues with some panels.
> +	 */
> +	if (intel_crtc_has_type(crtc_state, INTEL_OUTPUT_DSI) &&
> +	    IS_VALLEYVIEW(dev_priv))
> +		min_cdclk = max(320000, min_cdclk);
> +
>   	if (min_cdclk > dev_priv->max_cdclk_freq) {
>   		DRM_DEBUG_KMS("required cdclk (%d kHz) exceeds max (%d kHz)\n",
>   			      min_cdclk, dev_priv->max_cdclk_freq);
>