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SubjectRe: [PATCH] drm/stm: ltdc: add mode_valid()
Date
Hi Philippe,

Reviewed-by: Yannick Fertré <yannick.fertre@st.com>

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@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,
>
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