[PATCH 4/8] drm/vc4: hdmi: Check and warn if we can't reach 4kp60 frequencies

[Maxime Ripard <maxime@cerno.tech>]

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.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>
---
 drivers/gpu/drm/vc4/vc4_hdmi.c | 17 +++++++++++++++++
 drivers/gpu/drm/vc4/vc4_hdmi.h |  8 ++++++++
 2 files changed, 25 insertions(+)

diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
index b5bc742993a4..f05f6da286f7 100644
--- a/drivers/gpu/drm/vc4/vc4_hdmi.c
+++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
@@ -953,6 +953,9 @@ 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;
@@ -972,6 +975,9 @@ 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 && ((mode->clock * 1000) > HDMI_14_MAX_TMDS_CLK))
+		return MODE_CLOCK_HIGH;
+
 	return MODE_OK;
 }
 
@@ -1986,6 +1992,17 @@ 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_get_max_rate(vc4->hvs->core_clk);
+
+		if (max_rate < 550000000) {
+			drm_warn(drm, "The core clock cannot reach frequencies high enough to support 4k @ 60Hz.");
+			drm_warn(drm, "Please change your config.txt file to add hdmi_enable_4kp60 and force_turbo");
+			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;
-- 
2.29.2