[PATCH] drm/stm: ltdc: add mode_valid()

[Philippe CORNU]

On 04/25/2018 09:12 AM, Yannick FERTRE wrote:
> Hi Philippe,
> 
> Reviewed-by: Yannick Fertré <yannick.fertre at st.com>
> 

Applied on drm-misc-next.
Many thanks,
Philippe :-)

> On 04/17/2018 01:40 PM, Philippe Cornu wrote:
>> Add mode_valid() function to filter modes according to available
>> pll clock values and "preferred" modes. It is particularly
>> useful for hdmi modes that require precise pixel clocks.
>>
>> Note that "preferred" modes are always accepted:
>> - this is important for panels because panel clock tolerances are
>>     bigger than hdmi ones and there is no reason to not accept them
>>     (the fps may vary a little but it is not a problem).
>> - the hdmi preferred mode will be accepted too, but userland will
>>     be able to use others hdmi "valid" modes if necessary.
>>
>> Signed-off-by: Philippe Cornu <philippe.cornu at st.com>
>> ---
>>    drivers/gpu/drm/stm/ltdc.c | 38 ++++++++++++++++++++++++++++++++++++++
>>    1 file changed, 38 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/stm/ltdc.c b/drivers/gpu/drm/stm/ltdc.c
>> index 014cef8cef37..616191fe98ae 100644
>> --- a/drivers/gpu/drm/stm/ltdc.c
>> +++ b/drivers/gpu/drm/stm/ltdc.c
>> @@ -445,6 +445,43 @@ static void ltdc_crtc_atomic_disable(struct drm_crtc *crtc,
>>    	reg_set(ldev->regs, LTDC_SRCR, SRCR_IMR);
>>    }
>>    
>> +#define CLK_TOLERANCE_HZ 50
>> +
>> +static enum drm_mode_status
>> +ltdc_crtc_mode_valid(struct drm_crtc *crtc,
>> +		     const struct drm_display_mode *mode)
>> +{
>> +	struct ltdc_device *ldev = crtc_to_ltdc(crtc);
>> +	int target = mode->clock * 1000;
>> +	int target_min = target - CLK_TOLERANCE_HZ;
>> +	int target_max = target + CLK_TOLERANCE_HZ;
>> +	int result;
>> +
>> +	/*
>> +	 * Accept all "preferred" modes:
>> +	 * - this is important for panels because panel clock tolerances are
>> +	 *   bigger than hdmi ones and there is no reason to not accept them
>> +	 *   (the fps may vary a little but it is not a problem).
>> +	 * - the hdmi preferred mode will be accepted too, but userland will
>> +	 *   be able to use others hdmi "valid" modes if necessary.
>> +	 */
>> +	if (mode->type & DRM_MODE_TYPE_PREFERRED)
>> +		return MODE_OK;
>> +
>> +	result = clk_round_rate(ldev->pixel_clk, target);
>> +
>> +	DRM_DEBUG_DRIVER("clk rate target %d, available %d\n", target, result);
>> +
>> +	/*
>> +	 * Filter modes according to the clock value, particularly useful for
>> +	 * hdmi modes that require precise pixel clocks.
>> +	 */
>> +	if (result < target_min || result > target_max)
>> +		return MODE_CLOCK_RANGE;
>> +
>> +	return MODE_OK;
>> +}
>> +
>>    static bool ltdc_crtc_mode_fixup(struct drm_crtc *crtc,
>>    				 const struct drm_display_mode *mode,
>>    				 struct drm_display_mode *adjusted_mode)
>> @@ -559,6 +596,7 @@ static void ltdc_crtc_atomic_flush(struct drm_crtc *crtc,
>>    }
>>    
>>    static const struct drm_crtc_helper_funcs ltdc_crtc_helper_funcs = {
>> +	.mode_valid = ltdc_crtc_mode_valid,
>>    	.mode_fixup = ltdc_crtc_mode_fixup,
>>    	.mode_set_nofb = ltdc_crtc_mode_set_nofb,
>>    	.atomic_flush = ltdc_crtc_atomic_flush,