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

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Date:   Thu, 13 Oct 2022 11:27:19 +0200
From:   Marijn Suijten <marijn.suijten@...ainline.org>
To:     Abhinav Kumar <quic_abhinavk@...cinc.com>
Cc:     phone-devel@...r.kernel.org, ~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 2022-10-12 16:08:07, Abhinav Kumar wrote:
> 
> 
> 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

It is correct, and I suggested in [1] to either reorder this patch 7/10
after 8/10, or pull back the msm_host pointer argument into this patch.

[1]: https://lore.kernel.org/linux-arm-msm/20221011075119.tvn5j5jm6aqnhqv2@SoMainline.org/

- Marijn

> > 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;