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Message-ID: <5de320ad-4b95-38ee-7a71-ba76de1a7cf5@linaro.org>
Date: Sat, 10 Jun 2023 02:30:03 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Jessica Zhang <quic_jesszhan@...cinc.com>,
Rob Clark <robdclark@...il.com>,
Abhinav Kumar <quic_abhinavk@...cinc.com>,
Sean Paul <sean@...rly.run>, David Airlie <airlied@...il.com>,
Daniel Vetter <daniel@...ll.ch>,
Marijn Suijten <marijn.suijten@...ainline.org>
Cc: Konrad Dybcio <konrad.dybcio@...aro.org>,
linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 6/6] drm/msm/dsi: Document DSC related pclk_rate and
hdisplay calculations
On 10/06/2023 01:57, Jessica Zhang wrote:
> Add documentation comments explaining the pclk_rate and hdisplay math
> related to DSC.
>
> Signed-off-by: Jessica Zhang <quic_jesszhan@...cinc.com>
> ---
> drivers/gpu/drm/msm/dsi/dsi_host.c | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
> index fb1d3a25765f..aeaadc18bc7b 100644
> --- a/drivers/gpu/drm/msm/dsi/dsi_host.c
> +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
> @@ -564,6 +564,13 @@ void dsi_link_clk_disable_v2(struct msm_dsi_host *msm_host)
> static unsigned long dsi_adjust_pclk_for_compression(const struct drm_display_mode *mode,
> const struct drm_dsc_config *dsc)
> {
> + /*
> + * Adjust the pclk rate by calculating a new hdisplay proportional to
> + * the compression ratio such that:
> + * new_hdisplay = old_hdisplay * target_bpp / source_bpp
I'd say `* compressed_bpp / uncompressed_bpp'. This is easier to follow
than source and target.
> + *
> + * Porches need not be adjusted during compression.
> + */
> int new_hdisplay = DIV_ROUND_UP(mode->hdisplay * drm_dsc_get_bpp_int(dsc),
> dsc->bits_per_component * 3);
>
> @@ -961,6 +968,9 @@ static void dsi_timing_setup(struct msm_dsi_host *msm_host, bool is_bonded_dsi)
>
> /* Divide the display by 3 but keep back/font porch and
> * pulse width same
> + *
> + * hdisplay will be divided by 3 here to account for the fact
> + * that DPU sends 3 bytes per pclk cycle to DSI.
> */
> h_total -= hdisplay;
> hdisplay = DIV_ROUND_UP(msm_dsc_get_bytes_per_line(msm_host->dsc), 3);
>
--
With best wishes
Dmitry
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