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drm/msm/dsi: Document DSC related pclk_rate and hdisplay calculations

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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
This commit is contained in:
Dmitry Baryshkov 2024-02-08 17:23:08 +02:00
parent b0b621f41b
commit 3b56d27ba1
1 changed files with 31 additions and 2 deletions
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33
drivers/gpu/drm/msm/dsi/dsi_host.c
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@ -519,6 +519,25 @@ void dsi_link_clk_disable_v2(struct msm_dsi_host *msm_host)
clk_disable_unprepare(msm_host->byte_clk);
}
/**
* dsi_adjust_pclk_for_compression() - Adjust the pclk rate for compression case
* @mode: The selected mode for the DSI output
* @dsc: DRM DSC configuration for this DSI output
*
* Adjust the pclk rate by calculating a new hdisplay proportional to
* the compression ratio such that:
* new_hdisplay = old_hdisplay * compressed_bpp / uncompressed_bpp
*
* Porches do not need to be adjusted:
* - For VIDEO mode they are not compressed by DSC and are passed as is.
* - For CMD mode there are no actual porches. Instead these fields
* currently represent the overhead to the image data transfer. As such, they
* are calculated for the final mode parameters (after the compression) and
* are not to be adjusted too.
*
* FIXME: Reconsider this if/when CMD mode handling is rewritten to use
* transfer time and data overhead as a starting point of the calculations.
*/
static unsigned long dsi_adjust_pclk_for_compression(const struct drm_display_mode *mode,
const struct drm_dsc_config *dsc)
{
@ -941,8 +960,18 @@ static void dsi_timing_setup(struct msm_dsi_host *msm_host, bool is_bonded_dsi)
if (ret)
return;
/* Divide the display by 3 but keep back/font porch and
* pulse width same
/*
* DPU sends 3 bytes per pclk cycle to DSI. If widebus is
* enabled, bus width is extended to 6 bytes.
*
* Calculate the number of pclks needed to transmit one line of
* the compressed data.
* The back/font porch and pulse width are kept intact. For
* VIDEO mode they represent timing parameters rather than
* actual data transfer, see the documentation for
* dsi_adjust_pclk_for_compression(). For CMD mode they are
* unused anyway.
*/
h_total -= hdisplay;
if (wide_bus_enabled && !(msm_host->mode_flags & MIPI_DSI_MODE_VIDEO))