1 files changed, 38 insertions, 0 deletions

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,