drm/vc4: hdmi: Adjust HSM clock rate depending on pixel rate

The HSM clock needs to be setup at around 101% of the pixel rate. This
was done previously by setting the clock rate to 163.7MHz at probe time and
only check in mode_valid whether the mode pixel clock was under the pixel
clock +1% or not.

However, with 4k we need to change that frequency to a higher frequency
than 163.7MHz, and yet want to have the lowest clock as possible to have a
decent power saving.

Let's change that logic a bit by setting the clock rate of the HSM clock
to the pixel rate at encoder_enable time. This would work for the
BCM2711 that support 4k resolutions and has a clock that can provide it,
but we still have to take care of a 4k panel plugged on a BCM283x SoCs
that wouldn't be able to use those modes, so let's define the limit in
the variant.

Signed-off-by: Maxime Ripard <[email protected]>
Tested-by: Chanwoo Choi <[email protected]>
Tested-by: Hoegeun Kwon <[email protected]>
Tested-by: Stefan Wahren <[email protected]>
Reviewed-by: Dave Stevenson <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/7e692ddc231d33dd671e70ea04dd1dcf56c1ecb3.1599120059.git-series.maxime@cerno.tech

Author: mripard

drivers/gpu/drm/vc4/vc4_hdmi.c

@@ -53,7 +53,6 @@
 #include "vc4_hdmi_regs.h"
 #include "vc4_regs.h"
 
-#define HSM_CLOCK_FREQ 163682864
 #define CEC_CLOCK_FREQ 40000
 
 static int vc4_hdmi_debugfs_regs(struct seq_file *m, void *unused)
@@ -326,6 +325,7 @@ static void vc4_hdmi_encoder_disable(struct drm_encoder *encoder)
 	HDMI_WRITE(HDMI_VID_CTL,
 		   HDMI_READ(HDMI_VID_CTL) & ~VC4_HD_VID_CTL_ENABLE);
 
+	clk_disable_unprepare(vc4_hdmi->hsm_clock);
 	clk_disable_unprepare(vc4_hdmi->pixel_clock);
 
 	ret = pm_runtime_put(&vc4_hdmi->pdev->dev);
@@ -423,6 +423,7 @@ static void vc4_hdmi_encoder_enable(struct drm_encoder *encoder)
 	struct vc4_hdmi *vc4_hdmi = encoder_to_vc4_hdmi(encoder);
 	struct vc4_hdmi_encoder *vc4_encoder = to_vc4_hdmi_encoder(encoder);
 	bool debug_dump_regs = false;
+	unsigned long pixel_rate, hsm_rate;
 	int ret;
 
 	ret = pm_runtime_get_sync(&vc4_hdmi->pdev->dev);
@@ -431,9 +432,8 @@ static void vc4_hdmi_encoder_enable(struct drm_encoder *encoder)
 		return;
 	}
 
-	ret = clk_set_rate(vc4_hdmi->pixel_clock,
-			   mode->clock * 1000 *
-			   ((mode->flags & DRM_MODE_FLAG_DBLCLK) ? 2 : 1));
+	pixel_rate = mode->clock * 1000 * ((mode->flags & DRM_MODE_FLAG_DBLCLK) ? 2 : 1);
+	ret = clk_set_rate(vc4_hdmi->pixel_clock, pixel_rate);
 	if (ret) {
 		DRM_ERROR("Failed to set pixel clock rate: %d\n", ret);
 		return;
@@ -445,6 +445,36 @@ static void vc4_hdmi_encoder_enable(struct drm_encoder *encoder)
 		return;
 	}
 
+	/*
+	 * As stated in RPi's vc4 firmware "HDMI state machine (HSM) clock must
+	 * be faster than pixel clock, infinitesimally faster, tested in
+	 * simulation. Otherwise, exact value is unimportant for HDMI
+	 * operation." This conflicts with bcm2835's vc4 documentation, which
+	 * states HSM's clock has to be at least 108% of the pixel clock.
+	 *
+	 * Real life tests reveal that vc4's firmware statement holds up, and
+	 * users are able to use pixel clocks closer to HSM's, namely for
+	 * 1920x1200@60Hz. So it was decided to have leave a 1% margin between
+	 * both clocks. Which, for RPi0-3 implies a maximum pixel clock of
+	 * 162MHz.
+	 *
+	 * Additionally, the AXI clock needs to be at least 25% of
+	 * pixel clock, but HSM ends up being the limiting factor.
+	 */
+	hsm_rate = max_t(unsigned long, 120000000, (pixel_rate / 100) * 101);
+	ret = clk_set_rate(vc4_hdmi->hsm_clock, hsm_rate);
+	if (ret) {
+		DRM_ERROR("Failed to set HSM clock rate: %d\n", ret);
+		return;
+	}
+
+	ret = clk_prepare_enable(vc4_hdmi->hsm_clock);
+	if (ret) {
+		DRM_ERROR("Failed to turn on HSM clock: %d\n", ret);
+		clk_disable_unprepare(vc4_hdmi->pixel_clock);
+		return;
+	}
+
 	if (vc4_hdmi->variant->reset)
 		vc4_hdmi->variant->reset(vc4_hdmi);
 
@@ -559,23 +589,9 @@ static enum drm_mode_status
 vc4_hdmi_encoder_mode_valid(struct drm_encoder *encoder,
 			    const struct drm_display_mode *mode)
 {
-	/*
-	 * As stated in RPi's vc4 firmware "HDMI state machine (HSM) clock must
-	 * be faster than pixel clock, infinitesimally faster, tested in
-	 * simulation. Otherwise, exact value is unimportant for HDMI
-	 * operation." This conflicts with bcm2835's vc4 documentation, which
-	 * states HSM's clock has to be at least 108% of the pixel clock.
-	 *
-	 * Real life tests reveal that vc4's firmware statement holds up, and
-	 * users are able to use pixel clocks closer to HSM's, namely for
-	 * 1920x1200@60Hz. So it was decided to have leave a 1% margin between
-	 * both clocks. Which, for RPi0-3 implies a maximum pixel clock of
-	 * 162MHz.
-	 *
-	 * Additionally, the AXI clock needs to be at least 25% of
-	 * pixel clock, but HSM ends up being the limiting factor.
-	 */
-	if (mode->clock > HSM_CLOCK_FREQ / (1000 * 101 / 100))
+	struct vc4_hdmi *vc4_hdmi = encoder_to_vc4_hdmi(encoder);
+
+	if ((mode->clock * 1000) > vc4_hdmi->variant->max_pixel_clock)
 		return MODE_CLOCK_HIGH;
 
 	return MODE_OK;
@@ -1348,23 +1364,6 @@ static int vc4_hdmi_bind(struct device *dev, struct device *master, void *data)
 		return -EPROBE_DEFER;
 	}
 
-	/* This is the rate that is set by the firmware.  The number
-	 * needs to be a bit higher than the pixel clock rate
-	 * (generally 148.5Mhz).
-	 */
-	ret = clk_set_rate(vc4_hdmi->hsm_clock, HSM_CLOCK_FREQ);
-	if (ret) {
-		DRM_ERROR("Failed to set HSM clock rate: %d\n", ret);
-		goto err_put_i2c;
-	}
-
-	ret = clk_prepare_enable(vc4_hdmi->hsm_clock);
-	if (ret) {
-		DRM_ERROR("Failed to turn on HDMI state machine clock: %d\n",
-			  ret);
-		goto err_put_i2c;
-	}
-
 	/* Only use the GPIO HPD pin if present in the DT, otherwise
 	 * we'll use the HDMI core's register.
 	 */
@@ -1412,9 +1411,7 @@ static int vc4_hdmi_bind(struct device *dev, struct device *master, void *data)
 err_destroy_encoder:
 	drm_encoder_cleanup(encoder);
 err_unprepare_hsm:
-	clk_disable_unprepare(vc4_hdmi->hsm_clock);
 	pm_runtime_disable(dev);
-err_put_i2c:
 	put_device(&vc4_hdmi->ddc->dev);
 
 	return ret;
@@ -1453,7 +1450,6 @@ static void vc4_hdmi_unbind(struct device *dev, struct device *master,
 	vc4_hdmi_connector_destroy(&vc4_hdmi->connector);
 	drm_encoder_cleanup(&vc4_hdmi->encoder.base.base);
 
-	clk_disable_unprepare(vc4_hdmi->hsm_clock);
 	pm_runtime_disable(dev);
 
 	put_device(&vc4_hdmi->ddc->dev);
@@ -1478,6 +1474,7 @@ static int vc4_hdmi_dev_remove(struct platform_device *pdev)
 static const struct vc4_hdmi_variant bcm2835_variant = {
 	.encoder_type		= VC4_ENCODER_TYPE_HDMI0,
 	.debugfs_name		= "hdmi_regs",
+	.max_pixel_clock	= 162000000,
 	.cec_available		= true,
 	.registers		= vc4_hdmi_fields,
 	.num_registers		= ARRAY_SIZE(vc4_hdmi_fields),

drivers/gpu/drm/vc4/vc4_hdmi.h

@@ -36,6 +36,9 @@ struct vc4_hdmi_variant {
 	/* Set to true when the CEC support is available */
 	bool cec_available;
 
+	/* Maximum pixel clock supported by the controller (in Hz) */
+	unsigned long long max_pixel_clock;
+
 	/* List of the registers available on that variant */
 	const struct vc4_hdmi_register *registers;