[PATCH v4 09/12] drm/vc4: hdmi: Check and warn if we can't reach 4kp60 frequencies

[Maxime Ripard <maxime@xxxxxxxxxx>]

In order to reach the frequencies needed to output at 594MHz, the
firmware needs to be configured with the appropriate parameters in the
config.txt file (enable_hdmi_4kp60 and force_turbo).

Let's detect it at bind time, warn the user if we can't, and filter out
the relevant modes.

Acked-by: Thomas Zimmermann <tzimmermann@xxxxxxx>
Reviewed-by: Dave Stevenson <dave.stevenson@xxxxxxxxxxxxxxx>
Signed-off-by: Maxime Ripard <maxime@xxxxxxxxxx>
---
 drivers/gpu/drm/vc4/vc4_hdmi.c | 31 +++++++++++++++++++++++++++++++
 drivers/gpu/drm/vc4/vc4_hdmi.h |  8 ++++++++
 2 files changed, 39 insertions(+)

diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
index c50dc5a59b2f..01d24ce8a795 100644
--- a/drivers/gpu/drm/vc4/vc4_hdmi.c
+++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
@@ -94,6 +94,11 @@
 
 #define HDMI_14_MAX_TMDS_CLK   (340 * 1000 * 1000)
 
+static bool vc4_hdmi_mode_needs_scrambling(const struct drm_display_mode *mode)
+{
+	return (mode->clock * 1000) > HDMI_14_MAX_TMDS_CLK;
+}
+
 static int vc4_hdmi_debugfs_regs(struct seq_file *m, void *unused)
 {
 	struct drm_info_node *node = (struct drm_info_node *)m->private;
@@ -210,6 +215,18 @@ static int vc4_hdmi_connector_get_modes(struct drm_connector *connector)
 	ret = drm_add_edid_modes(connector, edid);
 	kfree(edid);
 
+	if (vc4_hdmi->disable_4kp60) {
+		struct drm_device *drm = connector->dev;
+		struct drm_display_mode *mode;
+
+		list_for_each_entry(mode, &connector->probed_modes, head) {
+			if (vc4_hdmi_mode_needs_scrambling(mode)) {
+				drm_warn_once(drm, "The core clock cannot reach frequencies high enough to support 4k @ 60Hz.");
+				drm_warn_once(drm, "Please change your config.txt file to add hdmi_enable_4kp60.");
+			}
+		}
+	}
+
 	return ret;
 }
 
@@ -959,6 +976,9 @@ static int vc4_hdmi_encoder_atomic_check(struct drm_encoder *encoder,
 	if (pixel_rate > vc4_hdmi->variant->max_pixel_clock)
 		return -EINVAL;
 
+	if (vc4_hdmi->disable_4kp60 && (pixel_rate > HDMI_14_MAX_TMDS_CLK))
+		return -EINVAL;
+
 	vc4_state->pixel_rate = pixel_rate;
 
 	return 0;
@@ -978,6 +998,9 @@ vc4_hdmi_encoder_mode_valid(struct drm_encoder *encoder,
 	if ((mode->clock * 1000) > vc4_hdmi->variant->max_pixel_clock)
 		return MODE_CLOCK_HIGH;
 
+	if (vc4_hdmi->disable_4kp60 && vc4_hdmi_mode_needs_scrambling(mode))
+		return MODE_CLOCK_HIGH;
+
 	return MODE_OK;
 }
 
@@ -1993,6 +2016,14 @@ static int vc4_hdmi_bind(struct device *dev, struct device *master, void *data)
 	vc4_hdmi->disable_wifi_frequencies =
 		of_property_read_bool(dev->of_node, "wifi-2.4ghz-coexistence");
 
+	if (variant->max_pixel_clock == 600000000) {
+		struct vc4_dev *vc4 = to_vc4_dev(drm);
+		long max_rate = clk_round_rate(vc4->hvs->core_clk, 550000000);
+
+		if (max_rate < 550000000)
+			vc4_hdmi->disable_4kp60 = true;
+	}
+
 	if (vc4_hdmi->variant->reset)
 		vc4_hdmi->variant->reset(vc4_hdmi);
 
diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.h b/drivers/gpu/drm/vc4/vc4_hdmi.h
index 3cebd1fd00fc..3cd021136402 100644
--- a/drivers/gpu/drm/vc4/vc4_hdmi.h
+++ b/drivers/gpu/drm/vc4/vc4_hdmi.h
@@ -154,6 +154,14 @@ struct vc4_hdmi {
 	 */
 	bool disable_wifi_frequencies;
 
+	/*
+	 * Even if HDMI0 on the RPi4 can output modes requiring a pixel
+	 * rate higher than 297MHz, it needs some adjustments in the
+	 * config.txt file to be able to do so and thus won't always be
+	 * available.
+	 */
+	bool disable_4kp60;
+
 	struct cec_adapter *cec_adap;
 	struct cec_msg cec_rx_msg;
 	bool cec_tx_ok;
-- 
2.31.1