Re: [PATCH v2] drm/i915/vlv: Add cdclk workaround for DSI

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Wed, Dec 20, 2017 at 11:50:17AM +0100, 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, to make sure this not
> causes regressions on other devices and the higher cdclk does not cause
> any problems on the following devices:
> -GP-electronic T701      1024x600   333333 KHz cdclk after this patch
> -PEAQ C1010              1920x1200  333333 KHz cdclk after this patch
> -PoV mobii-wintab-800w    800x1280  333333 KHz cdclk after this patch
> -Asus Transformer-T100TA 1368x768   320000 KHz cdclk after this patch
> 
> Also interesting wrt this is the comment in vlv_calc_cdclk about the
> existing workaround to avoid 200 Mhz as clock because that causes issues
> in some cases.

IIRC the 200 MHz clock never worked on any machine/display.

> 
> 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.
> 
> Changes in v2:
> -Change the commit message and the code comment to not treat the GOP as
>  a reference, the GOP should not be treated as a reference
> 
> Signed-off-by: Hans de Goede <hdegoede@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..a15976f55f47 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 some DSI panels loose (v|h)sync when the clock is lower

s/loose/lose/

My VLV+DSI tablet is happy with the 266 MHz cdclk, so it's a little
disappointing to apply this to all such machines. But unless someone
can come up with a better workaround I think this will have to do.

Acked-by: Ville Syrjälä <ville.syrjala@linux.intel.com>


> +	 * then 320000KHz.
> +	 */
> +	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

-- 
Ville Syrjälä
Intel OTC
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