linux-kernel - Re: [PATCH v3 07/10] drm/msm/dsi: Disallow 8 BPC DSC configuration for alternative BPC values

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Date:   Wed, 12 Oct 2022 16:08:07 -0700
From:   Abhinav Kumar <quic_abhinavk@...cinc.com>
To:     Marijn Suijten <marijn.suijten@...ainline.org>,
        <phone-devel@...r.kernel.org>
CC:     <~postmarketos/upstreaming@...ts.sr.ht>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...ainline.org>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Martin Botka <martin.botka@...ainline.org>,
        Jami Kettunen <jami.kettunen@...ainline.org>,
        Rob Clark <robdclark@...il.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>, Vinod Koul <vkoul@...nel.org>,
        Douglas Anderson <dianders@...omium.org>,
        Vladimir Lypak <vladimir.lypak@...il.com>,
        <linux-arm-msm@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
        <freedreno@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 07/10] drm/msm/dsi: Disallow 8 BPC DSC configuration
 for alternative BPC values



On 10/9/2022 11:51 AM, Marijn Suijten wrote:
> According to the `/* bpc 8 */` comment below only values for a
> bits_per_component of 8 are currently hardcoded in place.  This is
> further confirmed by downstream sources [1] containing different
> constants for other BPC values (and different initial_offset too,
> with an extra dependency on bits_per_pixel).  Prevent future mishaps by
> explicitly disallowing any other bits_per_component value until the
> right parameters are put in place and tested.
> 
> [1]: https://git.codelinaro.org/clo/la/platform/vendor/opensource/display-drivers/-/blob/DISPLAY.LA.2.0.r1-08000-WAIPIO.0/msm/sde_dsc_helper.c#L110-139
> 

Seems like a valid kbot error.

https://patchwork.freedesktop.org/patch/506359/#comment_912830

> Signed-off-by: Marijn Suijten <marijn.suijten@...ainline.org>
> ---
>   drivers/gpu/drm/msm/dsi/dsi_host.c | 5 +++++
>   1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
> index 68c39debc22f..7e6b7e506ae8 100644
> --- a/drivers/gpu/drm/msm/dsi/dsi_host.c
> +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
> @@ -1774,6 +1774,11 @@ static int dsi_populate_dsc_params(struct drm_dsc_config *dsc)
>   {
>   	int i;
>   
> +	if (dsc->bits_per_component != 8) {
> +		DRM_DEV_ERROR(&msm_host->pdev->dev, "DSI does not support bits_per_component != 8 yet\n");
> +		return -EOPNOTSUPP;
> +	}
> +
>   	dsc->rc_model_size = 8192;
>   	dsc->first_line_bpg_offset = 12;
>   	dsc->rc_edge_factor = 6;