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git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
drm/msm/dsi: Document DSC related pclk_rate and hdisplay calculations
Provide actual documentation for the pclk and hdisplay calculations in
the case of DSC compression being used.
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/577534/
Link: https://lore.kernel.org/r/20240208-fd_document_dsc_pclk_rate-v4-1-56fe59d0a2e0@linaro.org
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drivers/gpu/drm/msm/dsi/dsi_host.c
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drivers/gpu/drm/msm/dsi/dsi_host.c
···
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clk_disable_unprepare(msm_host->byte_clk);
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}
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/**
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* dsi_adjust_pclk_for_compression() - Adjust the pclk rate for compression case
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* @mode: The selected mode for the DSI output
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* @dsc: DRM DSC configuration for this DSI output
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*
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* Adjust the pclk rate by calculating a new hdisplay proportional to
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* the compression ratio such that:
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* new_hdisplay = old_hdisplay * compressed_bpp / uncompressed_bpp
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*
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* Porches do not need to be adjusted:
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* - For VIDEO mode they are not compressed by DSC and are passed as is.
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* - For CMD mode there are no actual porches. Instead these fields
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* currently represent the overhead to the image data transfer. As such, they
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* are calculated for the final mode parameters (after the compression) and
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* are not to be adjusted too.
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*
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* FIXME: Reconsider this if/when CMD mode handling is rewritten to use
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* transfer time and data overhead as a starting point of the calculations.
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*/
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static unsigned long dsi_adjust_pclk_for_compression(const struct drm_display_mode *mode,
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const struct drm_dsc_config *dsc)
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{
···
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if (ret)
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return;
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/* Divide the display by 3 but keep back/font porch and
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* pulse width same
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/*
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* DPU sends 3 bytes per pclk cycle to DSI. If widebus is
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* enabled, bus width is extended to 6 bytes.
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*
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* Calculate the number of pclks needed to transmit one line of
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* the compressed data.
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+
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* The back/font porch and pulse width are kept intact. For
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* VIDEO mode they represent timing parameters rather than
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* actual data transfer, see the documentation for
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* dsi_adjust_pclk_for_compression(). For CMD mode they are
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* unused anyway.
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*/
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h_total -= hdisplay;
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if (wide_bus_enabled && !(msm_host->mode_flags & MIPI_DSI_MODE_VIDEO))