drm/vc4: hdmi: Add more checks for 4k resolutions

At least the 4096x2160@60Hz mode requires some overclocking that isn't
available by default, even if hdmi_enable_4kp60 is enabled.

Let's add some logic to detect whether we can satisfy the core clock
requirements for that mode, and prevent it from being used otherwise.
Signed-off-by: Dom Cobley <popcornmix@gmail.com>
Reviewed-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Link: https://lore.kernel.org/r/20220815-rpi-fix-4k-60-v5-6-fe9e7ac8b111@cerno.techSigned-off-by: Maxime Ripard <maxime@cerno.tech>

drivers/gpu/drm/vc4/vc4_drv.h

@@ -347,6 +347,12 @@ struct vc4_hvs {
 	 * available.
 	 */
 	bool vc5_hdmi_enable_hdmi_20;
+
+	/*
+	 * 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

@@ -1753,6 +1753,7 @@ vc4_hdmi_sink_supports_format_bpc(const struct vc4_hdmi *vc4_hdmi,
 
 static enum drm_mode_status
 vc4_hdmi_encoder_clock_valid(const struct vc4_hdmi *vc4_hdmi,
+			     const struct drm_display_mode *mode,
 			     unsigned long long clock)
 {
 	const struct drm_connector *connector = &vc4_hdmi->connector;
@@ -1765,6 +1766,12 @@ vc4_hdmi_encoder_clock_valid(const struct vc4_hdmi *vc4_hdmi,
 	if (!vc4->hvs->vc5_hdmi_enable_hdmi_20 && clock > HDMI_14_MAX_TMDS_CLK)
 		return MODE_CLOCK_HIGH;
 
+	/* 4096x2160@60 is not reliable without overclocking core */
+	if (!vc4->hvs->vc5_hdmi_enable_4096by2160 &&
+	    mode->hdisplay > 3840 && mode->vdisplay >= 2160 &&
+	    drm_mode_vrefresh(mode) >= 50)
+		return MODE_CLOCK_HIGH;
+
 	if (info->max_tmds_clock && clock > (info->max_tmds_clock * 1000))
 		return MODE_CLOCK_HIGH;
 
@@ -1799,7 +1806,7 @@ vc4_hdmi_encoder_compute_clock(const struct vc4_hdmi *vc4_hdmi,
 	unsigned long long clock;
 
 	clock = vc4_hdmi_encoder_compute_mode_clock(mode, bpc, fmt);
-	if (vc4_hdmi_encoder_clock_valid(vc4_hdmi, clock) != MODE_OK)
+	if (vc4_hdmi_encoder_clock_valid(vc4_hdmi, mode, clock) != MODE_OK)
 		return -EINVAL;
 
 	vc4_state->tmds_char_rate = clock;
@@ -1962,7 +1969,7 @@ vc4_hdmi_encoder_mode_valid(struct drm_encoder *encoder,
 	     (mode->hsync_end % 2) || (mode->htotal % 2)))
 		return MODE_H_ILLEGAL;
 
-	return vc4_hdmi_encoder_clock_valid(vc4_hdmi, mode->clock * 1000);
+	return vc4_hdmi_encoder_clock_valid(vc4_hdmi, mode, mode->clock * 1000);
 }
 
 static const struct drm_encoder_helper_funcs vc4_hdmi_encoder_helper_funcs = {

drivers/gpu/drm/vc4/vc4_hvs.c

@@ -818,6 +818,9 @@ static int vc4_hvs_bind(struct device *dev, struct device *master, void *data)
 		if (max_rate >= 550000000)
 			hvs->vc5_hdmi_enable_hdmi_20 = true;
 
+		if (max_rate >= 600000000)
+			hvs->vc5_hdmi_enable_4096by2160 = true;
+
 		hvs->max_core_rate = max_rate;
 
 		ret = clk_prepare_enable(hvs->core_clk);