linux-kernel - Re: [PATCH v2 4/6] drm/msm/dsi: add a comment to explain pkt_per

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Date:   Wed, 15 Nov 2023 09:38:23 +0200
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Jonathan Marek <jonathan@...ek.ca>
Cc:     freedreno@...ts.freedesktop.org, Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Sean Paul <sean@...rly.run>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Jessica Zhang <quic_jesszhan@...cinc.com>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Jiasheng Jiang <jiasheng@...as.ac.cn>,
        "open list:DRM DRIVER FOR MSM ADRENO GPU" 
        <linux-arm-msm@...r.kernel.org>,
        "open list:DRM DRIVER FOR MSM ADRENO GPU" 
        <dri-devel@...ts.freedesktop.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 4/6] drm/msm/dsi: add a comment to explain pkt_per_line encoding

On Wed, 15 Nov 2023 at 01:00, Jonathan Marek <jonathan@...ek.ca> wrote:
>
> Make it clear why the pkt_per_line value is being "divided by 2".
>
> Signed-off-by: Jonathan Marek <jonathan@...ek.ca>
> ---
>  drivers/gpu/drm/msm/dsi/dsi_host.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
> index 66f198e21a7e..842765063b1b 100644
> --- a/drivers/gpu/drm/msm/dsi/dsi_host.c
> +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
> @@ -877,6 +877,8 @@ static void dsi_update_dsc_timing(struct msm_dsi_host *msm_host, bool is_cmd_mod
>         /* DSI_VIDEO_COMPRESSION_MODE & DSI_COMMAND_COMPRESSION_MODE
>          * registers have similar offsets, so for below common code use
>          * DSI_VIDEO_COMPRESSION_MODE_XXXX for setting bits
> +        *
> +        * pkt_per_line is log2 encoded, >>1 works for supported values (1,2,4)
>          */
>         reg |= DSI_VIDEO_COMPRESSION_MODE_CTRL_PKT_PER_LINE(pkt_per_line >> 1);

Should we switch to ffs() or fls() instead?

>         reg |= DSI_VIDEO_COMPRESSION_MODE_CTRL_EOL_BYTE_NUM(eol_byte_num);
> --
> 2.26.1
>


-- 
With best wishes
Dmitry