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

[Rodrigo Vivi]

On Tue, Dec 19, 2017 at 07:21:13PM +0000, 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

and lower clock shift the image in all of them?

> 
> 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.
> +	 */

Afaik (afai-have-noticed) GOP always use the higher freq and higher rates
that panels support with no care about saving any power. So I'm not sure if
that should be used as any sort of reference for us.

Note I'm not telling to not add the workaround itself...

> +	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);
> -- 
> 2.14.3
>