drm/stm: ltdc: filter mode pixel clock vs pad constraint

Filter the requested mode pixel clock frequency according
to the pad maximum supported frequency.
Signed-off-by: Yannick Fertre <yannick.fertre@st.com>
Reviewed-by: Philippe Cornu <philippe.cornu@st.com>
Tested-by: Philippe Cornu <philippe.cornu@st.com>
Signed-off-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/1530271342-5532-1-git-send-email-yannick.fertre@st.com

drivers/gpu/drm/stm/ltdc.c

@@ -457,6 +457,14 @@ ltdc_crtc_mode_valid(struct drm_crtc *crtc,
 	int target_max = target + CLK_TOLERANCE_HZ;
 	int result;
 
+	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 max frequency supported by the pads */
+	if (result > ldev->caps.pad_max_freq_hz)
+		return MODE_CLOCK_HIGH;
+
 	/*
 	 * Accept all "preferred" modes:
 	 * - this is important for panels because panel clock tolerances are
@@ -468,10 +476,6 @@ ltdc_crtc_mode_valid(struct drm_crtc *crtc,
 	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.
@@ -991,11 +995,15 @@ static int ltdc_get_caps(struct drm_device *ddev)
 		 * does not work on 2nd layer.
 		 */
 		ldev->caps.non_alpha_only_l1 = true;
+		ldev->caps.pad_max_freq_hz = 90000000;
+		if (ldev->caps.hw_version == HWVER_10200)
+			ldev->caps.pad_max_freq_hz = 65000000;
 		break;
 	case HWVER_20101:
 		ldev->caps.reg_ofs = REG_OFS_4;
 		ldev->caps.pix_fmt_hw = ltdc_pix_fmt_a1;
 		ldev->caps.non_alpha_only_l1 = false;
+		ldev->caps.pad_max_freq_hz = 150000000;
 		break;
 	default:
 		return -ENODEV;

drivers/gpu/drm/stm/ltdc.h

@@ -18,6 +18,7 @@ struct ltdc_caps {
 	u32 bus_width;		/* bus width (32 or 64 bits) */
 	const u32 *pix_fmt_hw;	/* supported pixel formats */
 	bool non_alpha_only_l1; /* non-native no-alpha formats on layer 1 */
+	int pad_max_freq_hz;	/* max frequency supported by pad */
 };
 
 #define LTDC_MAX_LAYER	4