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

[Hans de Goede]

Hi,

On 20-12-17 15:04, Ville Syrjälä wrote:
> 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 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..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 at linux.intel.com>

Thank you, I've just pushed this to dinq with your acked-by and
the spelling error corrected.

Regards,

Hans



>> +	 * 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
>