kms/vc4_hdmi: Refuse 4096x2160@60 hdmi modes

These are no reliable without overclocking.
See: raspberrypi/linux#5034

Signed-off-by: Dom Cobley <popcornmix@gmail.com>

drivers/gpu/drm/vc4/vc4_drv.h

@@ -342,6 +342,12 @@ struct vc4_hvs {
 	struct drm_mm_node mitchell_netravali_filter;
 
 	struct debugfs_regset32 regset;
+
+	/*
+	 * 4096x2160@60 requires a core overclock to work, so register
+	 * whether that is sufficient.
+	 */
+	bool vc5_hdmi_enable_4096by2160;
 };
 
 struct vc4_plane {

drivers/gpu/drm/vc4/vc4_hdmi.c

@@ -2089,6 +2089,7 @@ static int vc4_hdmi_encoder_atomic_check(struct drm_encoder *encoder,
 					 struct drm_crtc_state *crtc_state,
 					 struct drm_connector_state *conn_state)
 {
+	struct vc4_dev *vc4 = to_vc4_dev(encoder->dev);
 	struct vc4_hdmi *vc4_hdmi = encoder_to_vc4_hdmi(encoder);
 	struct drm_connector *connector = &vc4_hdmi->connector;
 	struct drm_connector_state *old_conn_state =
@@ -2121,6 +2122,12 @@ static int vc4_hdmi_encoder_atomic_check(struct drm_encoder *encoder,
 			return -EINVAL;
 	}
 
+	/* 4096x2160@60 is not reliable without overclocking core */
+	if (mode->hdisplay > 3840 && mode->vdisplay >= 2160 &&
+	    drm_mode_vrefresh(mode) >= 50 &&
+	    !vc4->hvs->vc5_hdmi_enable_4096by2160)
+		return -EINVAL;
+
 	/*
 	 * The 1440p@60 pixel rate is in the same range than the first
 	 * WiFi channel (between 2.4GHz and 2.422GHz with 22MHz
@@ -2152,13 +2159,20 @@ vc4_hdmi_encoder_mode_valid(struct drm_encoder *encoder,
 			    const struct drm_display_mode *mode)
 {
 	struct vc4_hdmi *vc4_hdmi = encoder_to_vc4_hdmi(encoder);
+	const struct drm_connector *connector = &vc4_hdmi->connector;
+	struct vc4_dev *vc4 = to_vc4_dev(connector->dev);
 
 	if (vc4_hdmi->variant->unsupported_odd_h_timings &&
 	    !(mode->flags & DRM_MODE_FLAG_DBLCLK) &&
 	    ((mode->hdisplay % 2) || (mode->hsync_start % 2) ||
 	     (mode->hsync_end % 2) || (mode->htotal % 2)))
 		return MODE_H_ILLEGAL;
 
+	if (mode->hdisplay > 3840 && mode->vdisplay >= 2160 &&
+	    drm_mode_vrefresh(mode) >= 50 &&
+	    !vc4->hvs->vc5_hdmi_enable_4096by2160)
+		return MODE_CLOCK_HIGH;
+
 	return vc4_hdmi_encoder_clock_valid(vc4_hdmi, mode->clock * 1000);
 }
 

drivers/gpu/drm/vc4/vc4_hvs.c

@@ -1022,12 +1022,18 @@ static int vc4_hvs_bind(struct device *dev, struct device *master, void *data)
 	hvs->regset.nregs = ARRAY_SIZE(hvs_regs);
 
 	if (vc4->is_vc5) {
+		unsigned long min_rate;
+
 		hvs->core_clk = devm_clk_get(&pdev->dev, NULL);
 		if (IS_ERR(hvs->core_clk)) {
 			dev_err(&pdev->dev, "Couldn't get core clock\n");
 			return PTR_ERR(hvs->core_clk);
 		}
 
+		min_rate = rpi_firmware_clk_get_min_rate(hvs->core_clk);
+		if (min_rate >= 600000000)
+			hvs->vc5_hdmi_enable_4096by2160 = true;
+
 		ret = clk_prepare_enable(hvs->core_clk);
 		if (ret) {
 			dev_err(&pdev->dev, "Couldn't enable the core clock\n");