[PATCH v9 08/27] drm/connector: hdmi: Add HDMI compute clock helper

Maxime Ripard
2024-03-11T14:50:24Z

A lot of HDMI drivers have some variation of the formula to calculate
the TMDS character rate from a mode, but few of them actually take all
parameters into account.

Let's create a helper to provide that rate taking all parameters into
account.

Reviewed-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Signed-off-by: Maxime Ripard <mripard@kernel.org>
---
drivers/gpu/drm/drm_connector.c | 71 +++++++++++++++++++++++++++++++++++++++++
include/drm/drm_connector.h | 5 +++
2 files changed, 76 insertions(+)

diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
index b629c8e990f4..8cc1332f11c2 100644
--- a/drivers/gpu/drm/drm_connector.c
+++ b/drivers/gpu/drm/drm_connector.c
@@ -2895,10 +2895,81 @@ void drm_connector_update_privacy_screen(const struct drm_connector_state *conne
/* The hw_state property value may have changed, update it. */
drm_connector_update_privacy_screen_properties(connector, false);
}
EXPORT_SYMBOL(drm_connector_update_privacy_screen);

+/**
+ * drm_connector_hdmi_compute_mode_clock() - Computes the TMDS Character Rate
+ * @mode: Display mode to compute the clock for
+ * @bpc: Bits per character
+ * @fmt: Output Pixel Format used
+ *
+ * Returns the TMDS Character Rate for a given mode, bpc count and output format.
+ *
+ * RETURNS:
+ * The TMDS Character Rate, in Hertz, or 0 on error.
+ */
+unsigned long long
+drm_connector_hdmi_compute_mode_clock(const struct drm_display_mode *mode,
+ unsigned int bpc,
+ enum hdmi_colorspace fmt)
+{
+ unsigned long long clock = mode->clock * 1000ULL;
+ unsigned int vic = drm_match_cea_mode(mode);
+
+ /*
+ * CTA-861-G Spec, section 5.4 - Color Coding and Quantization
+ * mandates that VIC 1 always uses 8 bpc.
+ */
+ if (vic == 1 && bpc != 8)
+ return 0;
+
+ /*
+ * HDMI 2.0 Spec, section 7.1 - YCbCr 4:2:0 Pixel Encoding
+ * specifies that YUV420 encoding is only available for those
+ * VICs.
+ */
+ if (fmt == HDMI_COLORSPACE_YUV420 &&
+ !(vic == 96 || vic == 97 || vic == 101 ||
+ vic == 102 || vic == 106 || vic == 107))
+ return 0;
+
+ if (fmt == HDMI_COLORSPACE_YUV422) {
+ /*
+ * HDMI 1.4b Spec, section 6.2.3 - Pixel Encoding Requirements
+ * specifies that YUV422 is 36-bit only.
+ */
+ if (bpc != 12)
+ return 0;
+
+ /*
+ * HDMI 1.0 Spec, section 6.5 - Pixel Encoding
+ * specifies that YUV422 requires two 12-bits components per
+ * pixel clock, which is equivalent in our calculation to three
+ * 8-bits components
+ */
+ bpc = 8;
+ }
+
+ /*
+ * HDMI 2.0 Spec, Section 7.1 - YCbCr 4:2:0 Pixel Encoding
+ * specifies that YUV420 encoding is carried at a TMDS Character Rate
+ * equal to half the pixel clock rate.
+ */
+ if (fmt == HDMI_COLORSPACE_YUV420)
+ clock = clock / 2;
+
+ if (mode->flags & DRM_MODE_FLAG_DBLCLK)
+ clock = clock * 2;
+
+ clock = clock * bpc;
+ do_div(clock, 8);
+
+ return clock;
+}
+EXPORT_SYMBOL(drm_connector_hdmi_compute_mode_clock);
+
int drm_connector_set_obj_prop(struct drm_mode_object *obj,
struct drm_property *property,
uint64_t value)
{
int ret = -EINVAL;
diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
index 29883e6f8e50..a859ad7ee04b 100644
--- a/include/drm/drm_connector.h
+++ b/include/drm/drm_connector.h
@@ -36,10 +36,11 @@

struct drm_connector_helper_funcs;
struct drm_modeset_acquire_ctx;
struct drm_device;
struct drm_crtc;
+struct drm_display_mode;
struct drm_encoder;
struct drm_panel;
struct drm_property;
struct drm_property_blob;
struct drm_printer;
@@ -2092,10 +2093,14 @@ int drm_connector_attach_max_bpc_property(struct drm_connector *connector,
void drm_connector_create_privacy_screen_properties(struct drm_connector *conn);
void drm_connector_attach_privacy_screen_properties(struct drm_connector *conn);
void drm_connector_attach_privacy_screen_provider(
struct drm_connector *connector, struct drm_privacy_screen *priv);
void drm_connector_update_privacy_screen(const struct drm_connector_state *connector_state);
+unsigned long long
+drm_connector_hdmi_compute_mode_clock(const struct drm_display_mode *mode,
+ unsigned int bpc,
+ enum hdmi_colorspace fmt);

/**
* struct drm_tile_group - Tile group metadata
* @refcount: reference count
* @dev: DRM device

--
2.43.2