From: Philippe CORNU <philippe.cornu@st.com>
Date: Tue, 17 Apr 2018 13:40:26 +0200
Subject: drm/stm: ltdc: add mode_valid()
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Git-commit: 0cefff963bf2af9ec9b2e2b537c3d3e6a43ceb9b
Patch-mainline: v4.18-rc1
References: FATE#326289 FATE#326079 FATE#326049 FATE#322398 FATE#326166

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>
Reviewed-by: Yannick Fertré <yannick.fertre@st.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180417114026.8709-1-philippe.cornu@st.com

Acked-by: Petr Tesarik <ptesarik@suse.com>
---
 drivers/gpu/drm/stm/ltdc.c |   38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

--- a/drivers/gpu/drm/stm/ltdc.c
+++ b/drivers/gpu/drm/stm/ltdc.c
@@ -445,6 +445,43 @@ static void ltdc_crtc_atomic_disable(str
 	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(struc
 }
 
 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,