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

[Yannick FERTRE]

Hi Philippe,

Reviewed-by: Yannick Fertrà <yannick.fertre@xxxxxx>

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@xxxxxx>
> ---
>   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,
>