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drm/display: hdmi: Add HDMI compute clock helper

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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>
Reviewed-by: Dmitry 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: Maxime Ripard <mripard@kernel.org>
This commit is contained in:
Maxime Ripard 2024-05-27 15:57:58 +02:00
parent 08eeaa134e
commit 40167bcbd1
No known key found for this signature in database
GPG Key ID: 275FCE19A23DBE76
2 changed files with 65 additions and 0 deletions
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61
drivers/gpu/drm/display/drm_hdmi_helper.c
View File

@ -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);

4
include/drm/display/drm_hdmi_helper.h
View File

@ -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