[PATCH v4 13/45] drm/connector: hdmi: Add HDMI compute clock helper

[Maxime Ripard]

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.

Signed-off-by: Maxime Ripard <mripard@xxxxxxxxxx>
---
 drivers/gpu/drm/drm_connector.c            |  59 ++++++
 drivers/gpu/drm/tests/drm_connector_test.c | 323 +++++++++++++++++++++++++++++
 include/drm/drm_connector.h                |   5 +
 3 files changed, 387 insertions(+)

diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
index e465109f131b..5eefeb868dbb 100644
--- a/drivers/gpu/drm/drm_connector.c
+++ b/drivers/gpu/drm/drm_connector.c
@@ -2976,6 +2976,65 @@ void drm_connector_update_privacy_screen(const struct drm_connector_state *conne
 }
 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;
+
+	/*
+	 * HDMI 1.4b Spec, section 6.2.3 - Pixel Encoding Requirements
+	 * specifies that YUV422 is 36-bit only.
+	 */
+	if (fmt == HDMI_COLORSPACE_YUV422 && bpc != 12)
+		return 0;
+
+	if (fmt == HDMI_COLORSPACE_YUV420)
+		clock = clock / 2;
+
+	if (mode->flags & DRM_MODE_FLAG_DBLCLK)
+		clock = clock * 2;
+
+	if (fmt == HDMI_COLORSPACE_YUV422)
+		bpc = 8;
+
+	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)
diff --git a/drivers/gpu/drm/tests/drm_connector_test.c b/drivers/gpu/drm/tests/drm_connector_test.c
index 502b7f9c1151..5262118cde85 100644
--- a/drivers/gpu/drm/tests/drm_connector_test.c
+++ b/drivers/gpu/drm/tests/drm_connector_test.c
@@ -8,7 +8,9 @@
 #include <drm/drm_atomic_state_helper.h>
 #include <drm/drm_connector.h>
 #include <drm/drm_drv.h>
+#include <drm/drm_edid.h>
 #include <drm/drm_kunit_helpers.h>
+#include <drm/drm_modes.h>
 
 #include <kunit/test.h>
 
@@ -823,10 +825,331 @@ static struct kunit_suite drm_connector_attach_broadcast_rgb_property_test_suite
 	.test_cases = drm_connector_attach_broadcast_rgb_property_tests,
 };
 
+/*
+ * Test that for a given mode, with 8bpc and an RGB output the TMDS
+ * character rate is equal to the mode pixel clock.
+ */
+static void drm_test_drm_connector_hdmi_compute_mode_clock_rgb(struct kunit *test)
+{
+	struct drm_connector_init_priv *priv = test->priv;
+	const struct drm_display_mode *mode;
+	unsigned long long rate;
+	struct drm_device *drm = &priv->drm;
+
+	mode = drm_display_mode_from_cea_vic(drm, 16);
+	KUNIT_ASSERT_NOT_NULL(test, mode);
+
+	KUNIT_ASSERT_FALSE(test, mode->flags & DRM_MODE_FLAG_DBLCLK);
+
+	rate = drm_connector_hdmi_compute_mode_clock(mode, 8, HDMI_COLORSPACE_RGB);
+	KUNIT_ASSERT_GT(test, rate, 0);
+	KUNIT_EXPECT_EQ(test, mode->clock * 1000ULL, rate);
+}
+
+/*
+ * Test that for a given mode, with 10bpc and an RGB output the TMDS
+ * character rate is equal to 1.25 times the mode pixel clock.
+ */
+static void drm_test_drm_connector_hdmi_compute_mode_clock_rgb_10bpc(struct kunit *test)
+{
+	struct drm_connector_init_priv *priv = test->priv;
+	const struct drm_display_mode *mode;
+	unsigned long long rate;
+	struct drm_device *drm = &priv->drm;
+
+	mode = drm_display_mode_from_cea_vic(drm, 16);
+	KUNIT_ASSERT_NOT_NULL(test, mode);
+
+	KUNIT_ASSERT_FALSE(test, mode->flags & DRM_MODE_FLAG_DBLCLK);
+
+	rate = drm_connector_hdmi_compute_mode_clock(mode, 10, HDMI_COLORSPACE_RGB);
+	KUNIT_ASSERT_GT(test, rate, 0);
+	KUNIT_EXPECT_EQ(test, mode->clock * 1250, rate);
+}
+
+/*
+ * Test that for the VIC-1 mode, with 10bpc and an RGB output the TMDS
+ * character rate computation fails.
+ */
+static void drm_test_drm_connector_hdmi_compute_mode_clock_rgb_10bpc_vic_1(struct kunit *test)
+{
+	struct drm_connector_init_priv *priv = test->priv;
+	const struct drm_display_mode *mode;
+	unsigned long long rate;
+	struct drm_device *drm = &priv->drm;
+
+	mode = drm_display_mode_from_cea_vic(drm, 1);
+	KUNIT_ASSERT_NOT_NULL(test, mode);
+
+	rate = drm_connector_hdmi_compute_mode_clock(mode, 10, HDMI_COLORSPACE_RGB);
+	KUNIT_EXPECT_EQ(test, rate, 0);
+}
+
+/*
+ * Test that for a given mode, with 12bpc and an RGB output the TMDS
+ * character rate is equal to 1.5 times the mode pixel clock.
+ */
+static void drm_test_drm_connector_hdmi_compute_mode_clock_rgb_12bpc(struct kunit *test)
+{
+	struct drm_connector_init_priv *priv = test->priv;
+	const struct drm_display_mode *mode;
+	unsigned long long rate;
+	struct drm_device *drm = &priv->drm;
+
+	mode = drm_display_mode_from_cea_vic(drm, 16);
+	KUNIT_ASSERT_NOT_NULL(test, mode);
+
+	KUNIT_ASSERT_FALSE(test, mode->flags & DRM_MODE_FLAG_DBLCLK);
+
+	rate = drm_connector_hdmi_compute_mode_clock(mode, 12, HDMI_COLORSPACE_RGB);
+	KUNIT_ASSERT_GT(test, rate, 0);
+	KUNIT_EXPECT_EQ(test, mode->clock * 1500, rate);
+}
+
+/*
+ * Test that for the VIC-1 mode, with 12bpc and an RGB output the TMDS
+ * character rate computation fails.
+ */
+static void drm_test_drm_connector_hdmi_compute_mode_clock_rgb_12bpc_vic_1(struct kunit *test)
+{
+	struct drm_connector_init_priv *priv = test->priv;
+	const struct drm_display_mode *mode;
+	unsigned long long rate;
+	struct drm_device *drm = &priv->drm;
+
+	mode = drm_display_mode_from_cea_vic(drm, 1);
+	KUNIT_ASSERT_NOT_NULL(test, mode);
+
+	rate = drm_connector_hdmi_compute_mode_clock(mode, 12, HDMI_COLORSPACE_RGB);
+	KUNIT_EXPECT_EQ(test, rate, 0);
+}
+
+/*
+ * Test that for a mode with the pixel repetition flag, the TMDS
+ * character rate is indeed double the mode pixel clock.
+ */
+static void drm_test_drm_connector_hdmi_compute_mode_clock_rgb_double(struct kunit *test)
+{
+	struct drm_connector_init_priv *priv = test->priv;
+	const struct drm_display_mode *mode;
+	unsigned long long rate;
+	struct drm_device *drm = &priv->drm;
+
+	mode = drm_display_mode_from_cea_vic(drm, 6);
+	KUNIT_ASSERT_NOT_NULL(test, mode);
+
+	KUNIT_ASSERT_TRUE(test, mode->flags & DRM_MODE_FLAG_DBLCLK);
+
+	rate = drm_connector_hdmi_compute_mode_clock(mode, 8, HDMI_COLORSPACE_RGB);
+	KUNIT_ASSERT_GT(test, rate, 0);
+	KUNIT_EXPECT_EQ(test, (mode->clock * 1000ULL) * 2, rate);
+}
+
+/*
+ * Test that the TMDS character rate computation for the VIC modes
+ * explicitly listed in the spec as supporting YUV420 succeed and return
+ * half the mode pixel clock.
+ */
+static void drm_test_connector_hdmi_compute_mode_clock_yuv420_valid(struct kunit *test)
+{
+	struct drm_connector_init_priv *priv = test->priv;
+	const struct drm_display_mode *mode;
+	struct drm_device *drm = &priv->drm;
+	unsigned long long rate;
+	unsigned int vic = *(unsigned int *)test->param_value;
+
+	mode = drm_display_mode_from_cea_vic(drm, vic);
+	KUNIT_ASSERT_NOT_NULL(test, mode);
+
+	KUNIT_ASSERT_FALSE(test, mode->flags & DRM_MODE_FLAG_DBLCLK);
+
+	rate = drm_connector_hdmi_compute_mode_clock(mode, 8, HDMI_COLORSPACE_YUV420);
+	KUNIT_ASSERT_GT(test, rate, 0);
+	KUNIT_EXPECT_EQ(test, (mode->clock * 1000ULL) / 2, rate);
+}
+
+static const unsigned int drm_connector_hdmi_compute_mode_clock_yuv420_vic_valid_tests[] = {
+	96, 97, 101, 102, 106, 107,
+};
+
+static void drm_connector_hdmi_compute_mode_clock_yuv420_vic_desc(const unsigned int *vic, char *desc)
+{
+	sprintf(desc, "VIC %u", *vic);
+}
+
+KUNIT_ARRAY_PARAM(drm_connector_hdmi_compute_mode_clock_yuv420_valid,
+		  drm_connector_hdmi_compute_mode_clock_yuv420_vic_valid_tests,
+		  drm_connector_hdmi_compute_mode_clock_yuv420_vic_desc);
+
+/*
+ * Test that trying to compute the TMDS char rate with the YUV420 format
+ * for a mode that doesn't support the YUV420 encoding returns an error.
+ *
+ * TODO: We should probably test this with all the VIC but the
+ * explicitly supported ones. Since the list of VIC is quite long and
+ * not linear, the best way to support it at the moment would be to
+ * create a custom gen_params function that would only return valid
+ * VICs. At the moment, that function expects to get a pointer back
+ * however, and compilers don't really like casting between integer and
+ * pointers.
+ */
+static void drm_test_connector_hdmi_compute_mode_clock_yuv420_invalid(struct kunit *test)
+{
+	struct drm_connector_init_priv *priv = test->priv;
+	const struct drm_display_mode *mode;
+	struct drm_device *drm = &priv->drm;
+	unsigned long long rate;
+
+	mode = drm_display_mode_from_cea_vic(drm, 42);
+	KUNIT_ASSERT_NOT_NULL(test, mode);
+
+	KUNIT_ASSERT_FALSE(test, mode->flags & DRM_MODE_FLAG_DBLCLK);
+
+	rate = drm_connector_hdmi_compute_mode_clock(mode, 8, HDMI_COLORSPACE_YUV420);
+	KUNIT_EXPECT_EQ(test, rate, 0);
+}
+
+/*
+ * Test that for a given mode listed supporting it and an YUV420 output
+ * with 10bpc, the TMDS character rate is equal to 0.625 times the mode
+ * pixel clock.
+ */
+static void drm_test_connector_hdmi_compute_mode_clock_yuv420_10_bpc(struct kunit *test)
+{
+	struct drm_connector_init_priv *priv = test->priv;
+	const struct drm_display_mode *mode;
+	struct drm_device *drm = &priv->drm;
+	unsigned int vic =
+		drm_connector_hdmi_compute_mode_clock_yuv420_vic_valid_tests[0];
+	unsigned long long rate;
+
+	mode = drm_display_mode_from_cea_vic(drm, vic);
+	KUNIT_ASSERT_NOT_NULL(test, mode);
+
+	KUNIT_ASSERT_FALSE(test, mode->flags & DRM_MODE_FLAG_DBLCLK);
+
+	rate = drm_connector_hdmi_compute_mode_clock(mode, 10, HDMI_COLORSPACE_YUV420);
+	KUNIT_ASSERT_GT(test, rate, 0);
+
+	KUNIT_EXPECT_EQ(test, mode->clock * 625, rate);
+}
+
+/*
+ * Test that for a given mode listed supporting it and an YUV420 output
+ * with 12bpc, the TMDS character rate is equal to 0.75 times the mode
+ * pixel clock.
+ */
+static void drm_test_connector_hdmi_compute_mode_clock_yuv420_12_bpc(struct kunit *test)
+{
+	struct drm_connector_init_priv *priv = test->priv;
+	const struct drm_display_mode *mode;
+	struct drm_device *drm = &priv->drm;
+	unsigned int vic =
+		drm_connector_hdmi_compute_mode_clock_yuv420_vic_valid_tests[0];
+	unsigned long long rate;
+
+	mode = drm_display_mode_from_cea_vic(drm, vic);
+	KUNIT_ASSERT_NOT_NULL(test, mode);
+
+	KUNIT_ASSERT_FALSE(test, mode->flags & DRM_MODE_FLAG_DBLCLK);
+
+	rate = drm_connector_hdmi_compute_mode_clock(mode, 12, HDMI_COLORSPACE_YUV420);
+	KUNIT_ASSERT_GT(test, rate, 0);
+
+	KUNIT_EXPECT_EQ(test, mode->clock * 750, rate);
+}
+
+/*
+ * Test that for a given mode, the computation of the TMDS character
+ * rate with 8bpc and a YUV422 output fails.
+ */
+static void drm_test_connector_hdmi_compute_mode_clock_yuv422_8_bpc(struct kunit *test)
+{
+	struct drm_connector_init_priv *priv = test->priv;
+	const struct drm_display_mode *mode;
+	struct drm_device *drm = &priv->drm;
+	unsigned long long rate;
+
+	mode = drm_display_mode_from_cea_vic(drm, 16);
+	KUNIT_ASSERT_NOT_NULL(test, mode);
+
+	KUNIT_ASSERT_FALSE(test, mode->flags & DRM_MODE_FLAG_DBLCLK);
+
+	rate = drm_connector_hdmi_compute_mode_clock(mode, 8, HDMI_COLORSPACE_YUV422);
+	KUNIT_EXPECT_EQ(test, rate, 0);
+}
+
+/*
+ * Test that for a given mode, the computation of the TMDS character
+ * rate with 10bpc and a YUV422 output fails.
+ */
+static void drm_test_connector_hdmi_compute_mode_clock_yuv422_10_bpc(struct kunit *test)
+{
+	struct drm_connector_init_priv *priv = test->priv;
+	const struct drm_display_mode *mode;
+	struct drm_device *drm = &priv->drm;
+	unsigned long long rate;
+
+	mode = drm_display_mode_from_cea_vic(drm, 16);
+	KUNIT_ASSERT_NOT_NULL(test, mode);
+
+	KUNIT_ASSERT_FALSE(test, mode->flags & DRM_MODE_FLAG_DBLCLK);
+
+	rate = drm_connector_hdmi_compute_mode_clock(mode, 10, HDMI_COLORSPACE_YUV422);
+	KUNIT_EXPECT_EQ(test, rate, 0);
+}
+
+/*
+ * Test that for a given mode, the computation of the TMDS character
+ * rate with 12bpc and a YUV422 output succeeds and returns a rate equal
+ * to the mode pixel clock.
+ */
+static void drm_test_connector_hdmi_compute_mode_clock_yuv422_12_bpc(struct kunit *test)
+{
+	struct drm_connector_init_priv *priv = test->priv;
+	const struct drm_display_mode *mode;
+	struct drm_device *drm = &priv->drm;
+	unsigned long long rate;
+
+	mode = drm_display_mode_from_cea_vic(drm, 16);
+	KUNIT_ASSERT_NOT_NULL(test, mode);
+
+	KUNIT_ASSERT_FALSE(test, mode->flags & DRM_MODE_FLAG_DBLCLK);
+
+	rate = drm_connector_hdmi_compute_mode_clock(mode, 12, HDMI_COLORSPACE_YUV422);
+	KUNIT_ASSERT_GT(test, rate, 0);
+	KUNIT_EXPECT_EQ(test, mode->clock * 1000, rate);
+}
+
+static struct kunit_case drm_connector_hdmi_compute_mode_clock_tests[] = {
+	KUNIT_CASE(drm_test_drm_connector_hdmi_compute_mode_clock_rgb),
+	KUNIT_CASE(drm_test_drm_connector_hdmi_compute_mode_clock_rgb_10bpc),
+	KUNIT_CASE(drm_test_drm_connector_hdmi_compute_mode_clock_rgb_10bpc_vic_1),
+	KUNIT_CASE(drm_test_drm_connector_hdmi_compute_mode_clock_rgb_12bpc),
+	KUNIT_CASE(drm_test_drm_connector_hdmi_compute_mode_clock_rgb_12bpc_vic_1),
+	KUNIT_CASE(drm_test_drm_connector_hdmi_compute_mode_clock_rgb_double),
+	KUNIT_CASE_PARAM(drm_test_connector_hdmi_compute_mode_clock_yuv420_valid,
+			 drm_connector_hdmi_compute_mode_clock_yuv420_valid_gen_params),
+	KUNIT_CASE(drm_test_connector_hdmi_compute_mode_clock_yuv420_invalid),
+	KUNIT_CASE(drm_test_connector_hdmi_compute_mode_clock_yuv420_10_bpc),
+	KUNIT_CASE(drm_test_connector_hdmi_compute_mode_clock_yuv420_12_bpc),
+	KUNIT_CASE(drm_test_connector_hdmi_compute_mode_clock_yuv422_8_bpc),
+	KUNIT_CASE(drm_test_connector_hdmi_compute_mode_clock_yuv422_10_bpc),
+	KUNIT_CASE(drm_test_connector_hdmi_compute_mode_clock_yuv422_12_bpc),
+	{ }
+};
+
+static struct kunit_suite drm_connector_hdmi_compute_mode_clock_test_suite = {
+	.name = "drm_test_connector_hdmi_compute_mode_clock",
+	.init = drm_test_connector_init,
+	.test_cases = drm_connector_hdmi_compute_mode_clock_tests,
+};
+
 kunit_test_suites(
 	&drmm_connector_hdmi_init_test_suite,
 	&drmm_connector_init_test_suite,
 	&drm_connector_attach_broadcast_rgb_property_test_suite,
+	&drm_connector_hdmi_compute_mode_clock_test_suite,
 	&drm_get_tv_mode_from_name_test_suite,
 	&drm_hdmi_connector_get_broadcast_rgb_name_test_suite,
 	&drm_hdmi_connector_get_output_format_name_test_suite
diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
index 74db5ce47e01..0cc5a8732664 100644
--- a/include/drm/drm_connector.h
+++ b/include/drm/drm_connector.h
@@ -38,6 +38,7 @@ 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;
@@ -2136,6 +2137,10 @@ 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

-- 
2.41.0