linux-kernel - [PATCH v14 09/28] drm/display: hdmi: Add HDMI compute clock helper

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Message-Id: <20240521-kms-hdmi-connector-state-v14-9-51950db4fedb@kernel.org>
Date: Tue, 21 May 2024 12:13:42 +0200
From: Maxime Ripard <mripard@...nel.org>
To: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
 Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, 
 Daniel Vetter <daniel@...ll.ch>, Jonathan Corbet <corbet@....net>, 
 Sandy Huang <hjc@...k-chips.com>, 
 Heiko Stübner <heiko@...ech.de>, 
 Chen-Yu Tsai <wens@...e.org>, Jernej Skrabec <jernej.skrabec@...il.com>, 
 Samuel Holland <samuel@...lland.org>, Andy Yan <andy.yan@...k-chips.com>
Cc: Hans Verkuil <hverkuil@...all.nl>, 
 Sebastian Wick <sebastian.wick@...hat.com>, 
 Ville Syrjälä <ville.syrjala@...ux.intel.com>, 
 dri-devel@...ts.freedesktop.org, linux-arm-kernel@...ts.infradead.org, 
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, 
 linux-media@...r.kernel.org, linux-rockchip@...ts.infradead.org, 
 linux-sunxi@...ts.linux.dev, Maxime Ripard <mripard@...nel.org>, 
 Dave Stevenson <dave.stevenson@...pberrypi.com>
Subject: [PATCH v14 09/28] drm/display: hdmi: Add HDMI compute clock helper

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@...pberrypi.com>
Signed-off-by: Maxime Ripard <mripard@...nel.org>
---
 drivers/gpu/drm/display/drm_hdmi_helper.c | 57 +++++++++++++++++++++++++++++++
 include/drm/display/drm_hdmi_helper.h     |  4 +++
 2 files changed, 61 insertions(+)

diff --git a/drivers/gpu/drm/display/drm_hdmi_helper.c b/drivers/gpu/drm/display/drm_hdmi_helper.c
index faf5e9efa7d3..679eb3e81393 100644
--- a/drivers/gpu/drm/display/drm_hdmi_helper.c
+++ b/drivers/gpu/drm/display/drm_hdmi_helper.c
@@ -193,5 +193,62 @@ void drm_hdmi_avi_infoframe_content_type(struct hdmi_avi_infoframe *frame,
 	}
 
 	frame->itc = conn_state->content_type != DRM_MODE_CONTENT_TYPE_NO_DATA;
 }
 EXPORT_SYMBOL(drm_hdmi_avi_infoframe_content_type);
+
+/**
+ * drm_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_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;
+
+	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;
+
+	return DIV_ROUND_CLOSEST_ULL(clock * bpc, 8);
+}
+EXPORT_SYMBOL(drm_hdmi_compute_mode_clock);
diff --git a/include/drm/display/drm_hdmi_helper.h b/include/drm/display/drm_hdmi_helper.h
index 76d234826e22..57e3b18c15ec 100644
--- a/include/drm/display/drm_hdmi_helper.h
+++ b/include/drm/display/drm_hdmi_helper.h
@@ -22,6 +22,10 @@ drm_hdmi_infoframe_set_hdr_metadata(struct hdmi_drm_infoframe *frame,
 				    const struct drm_connector_state *conn_state);
 
 void drm_hdmi_avi_infoframe_content_type(struct hdmi_avi_infoframe *frame,
 					 const struct drm_connector_state *conn_state);
 
+unsigned long long
+drm_hdmi_compute_mode_clock(const struct drm_display_mode *mode,
+			    unsigned int bpc, enum hdmi_colorspace fmt);
+
 #endif

-- 
2.45.0