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git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
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@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>
+65
+61
drivers/gpu/drm/display/drm_hdmi_helper.c
+61
drivers/gpu/drm/display/drm_hdmi_helper.c
···
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frame->itc = conn_state->content_type != DRM_MODE_CONTENT_TYPE_NO_DATA;
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}
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EXPORT_SYMBOL(drm_hdmi_avi_infoframe_content_type);
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+
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/**
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* drm_hdmi_compute_mode_clock() - Computes the TMDS Character Rate
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* @mode: Display mode to compute the clock for
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* @bpc: Bits per character
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* @fmt: Output Pixel Format used
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*
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* Returns the TMDS Character Rate for a given mode, bpc count and output format.
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*
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* RETURNS:
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* The TMDS Character Rate, in Hertz, or 0 on error.
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*/
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unsigned long long
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drm_hdmi_compute_mode_clock(const struct drm_display_mode *mode,
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unsigned int bpc, enum hdmi_colorspace fmt)
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{
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unsigned long long clock = mode->clock * 1000ULL;
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unsigned int vic = drm_match_cea_mode(mode);
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/*
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* CTA-861-G Spec, section 5.4 - Color Coding and Quantization
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* mandates that VIC 1 always uses 8 bpc.
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*/
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if (vic == 1 && bpc != 8)
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return 0;
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if (fmt == HDMI_COLORSPACE_YUV422) {
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/*
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* HDMI 1.0 Spec, section 6.5 - Pixel Encoding states that
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* YUV422 sends 24 bits over three channels, with Cb and Cr
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* components being sent on odd and even pixels, respectively.
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*
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* If fewer than 12 bpc are sent, data are left justified.
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*/
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if (bpc > 12)
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return 0;
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/*
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* HDMI 1.0 Spec, section 6.5 - Pixel Encoding
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* specifies that YUV422 sends two 12-bits components over
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* three TMDS channels per pixel clock, which is equivalent to
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* three 8-bits components over three channels used by RGB as
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* far as the clock rate goes.
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*/
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bpc = 8;
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}
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/*
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* HDMI 2.0 Spec, Section 7.1 - YCbCr 4:2:0 Pixel Encoding
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* specifies that YUV420 encoding is carried at a TMDS Character Rate
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* equal to half the pixel clock rate.
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*/
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if (fmt == HDMI_COLORSPACE_YUV420)
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clock = clock / 2;
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if (mode->flags & DRM_MODE_FLAG_DBLCLK)
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clock = clock * 2;
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return DIV_ROUND_CLOSEST_ULL(clock * bpc, 8);
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}
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EXPORT_SYMBOL(drm_hdmi_compute_mode_clock);
+4
include/drm/display/drm_hdmi_helper.h
+4
include/drm/display/drm_hdmi_helper.h
···
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void drm_hdmi_avi_infoframe_content_type(struct hdmi_avi_infoframe *frame,
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const struct drm_connector_state *conn_state);
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unsigned long long
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drm_hdmi_compute_mode_clock(const struct drm_display_mode *mode,
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unsigned int bpc, enum hdmi_colorspace fmt);
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#endif