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Subject[PATCH v3 091/105] drm/vc4: hdmi: Adjust HSM clock rate depending on pixel rate
Date
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 <maxime@cerno.tech>
---
drivers/gpu/drm/vc4/vc4_hdmi.c | 79 ++++++++++++++++-------------------
drivers/gpu/drm/vc4/vc4_hdmi.h | 3 +-
2 files changed, 41 insertions(+), 41 deletions(-)

diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
index e816e5ab9a51..eda48f58dc01 100644
--- a/drivers/gpu/drm/vc4/vc4_hdmi.c
+++ b/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;
@@ -1345,23 +1361,6 @@ 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.
*/
@@ -1409,9 +1408,7 @@ 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;
@@ -1434,7 +1431,6 @@ 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);
@@ -1459,6 +1455,7 @@ 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),
diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.h b/drivers/gpu/drm/vc4/vc4_hdmi.h
index 20e0f5498f1e..9a6831b941d9 100644
--- a/drivers/gpu/drm/vc4/vc4_hdmi.h
+++ b/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;

--
git-series 0.9.1
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