Unverified Commit 40167bcb authored by Maxime Ripard's avatar Maxime Ripard
Browse files

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: default avatarDave Stevenson <dave.stevenson@raspberrypi.com>
Reviewed-by: default avatarDmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240527-kms-hdmi-connector-state-v15-9-c5af16c3aae2@kernel.org


Signed-off-by: default avatarMaxime Ripard <mripard@kernel.org>
parent 08eeaa13

drivers/gpu/drm/display/drm_hdmi_helper.c

+61 −0
Original line number Diff line number Diff line
@@ -195,3 +195,64 @@ 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 1.0 Spec, section 6.5 - Pixel Encoding states that

		 * YUV422 sends 24 bits over three channels, with Cb and Cr

		 * components being sent on odd and even pixels, respectively.

		 *

		 * If fewer than 12 bpc are sent, data are left justified.

		 */

		if (bpc > 12)

			return 0;



		/*

		 * HDMI 1.0 Spec, section 6.5 - Pixel Encoding

		 * specifies that YUV422 sends two 12-bits components over

		 * three TMDS channels per pixel clock, which is equivalent to

		 * three 8-bits components over three channels used by RGB as

		 * far as the clock rate goes.

		 */

		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);

include/drm/display/drm_hdmi_helper.h

+4 −0
Original line number Diff line number Diff line
@@ -24,4 +24,8 @@ drm_hdmi_infoframe_set_hdr_metadata(struct hdmi_drm_infoframe *frame, 
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