linux-kernel - Re: [PATCH v12,2/3] drm: mediatek: Set dpi format in mmsys

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Date:   Fri, 21 Oct 2022 11:39:12 -0400
From:   Nícolas F. R. A. Prado 
        <nfraprado@...labora.com>
To:     "xinlei.lee" <xinlei.lee@...iatek.com>
Cc:     matthias.bgg@...il.com, rex-bc.chen@...iatek.com,
        angelogioacchino.delregno@...labora.com, jason-jh.lin@...iatek.com,
        chunkuang.hu@...nel.org, p.zabel@...gutronix.de, airlied@...ux.ie,
        daniel@...ll.ch, dri-devel@...ts.freedesktop.org,
        linux-mediatek@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Project_Global_Chrome_Upstream_Group@...iatek.com,
        Jitao Shi <jitao.shi@...iatek.com>
Subject: Re: [PATCH v12,2/3] drm: mediatek: Set dpi format in mmsys

On Fri, Oct 21, 2022 at 08:18:25PM +0800, xinlei.lee wrote:
> On Thu, 2022-10-20 at 12:40 -0400, Nícolas F. R. A. Prado wrote:
> > On Wed, Oct 19, 2022 at 10:52:15AM +0800, xinlei.lee@...iatek.com
> > wrote:
[..]
> > > @@ -448,8 +453,12 @@ static void mtk_dpi_dual_edge(struct mtk_dpi
> > > *dpi)
> > >  		mtk_dpi_mask(dpi, DPI_OUTPUT_SETTING,
> > >  			     dpi->output_fmt ==
> > > MEDIA_BUS_FMT_RGB888_2X12_LE ?
> > >  			     EDGE_SEL : 0, EDGE_SEL);
> > > +		if (dpi->conf->edge_cfg_in_mmsys)
> > > +			mtk_mmsys_ddp_dpi_fmt_config(dpi->mmsys_dev,
> > > MTK_DPI_RGB888_DDR_CON);
> > >  	} else {
> > >  		mtk_dpi_mask(dpi, DPI_DDR_SETTING, DDR_EN | DDR_4PHASE,
> > > 0);
> > > +		if (dpi->conf->edge_cfg_in_mmsys)
> > > +			mtk_mmsys_ddp_dpi_fmt_config(dpi->mmsys_dev,
> > > MTK_DPI_RGB888_SDR_CON);
> > 
> > I know this isn't one of the formats supported by MT8186, but since
> > we're using
> > platform-agnostic formats now... This else branch in theory could
> > also run for a
> > format like MEDIA_BUS_FMT_YUYV8_1X16. Would it make sense to set
> > MTK_DPI_RGB888_SDR_CON in that case?
> > 
> > Thanks,
> > Nícolas
> > 
> > >  	}
> > 
> > [..]
> 
> Hi Nícolas:
> 
> Thanks for your review!
>  
> You are right, I understand you think this MTK_DPI_RGB888_SDR_CON 
> format seems useless as it will not be set, I confirmed with the 
> designer how the setting in mmsys affects the output format of the 
> MT8186, this mmsys setting will not be used by other ICs.
> 
> As mentioned earlier, the mmsys setting will make the MT8186dpi have 
> four output formats, even though the MT8186 dpi may not use them all.
> 
> So what needs to change here?

We could check that the format in the else path is a single edge RGB888 format
like MEDIA_BUS_FMT_RGB888_1X24 before setting the mmsys config, but there are
also other formats possible, and I actually don't think it's worth it to
complicate the logic further to protect from an edge-case that can't be hit
yet...

So just leave it as it is. We can worry about it when/if a non-RGB888 single
edge format needs to be setup on mmsys.

So,

Reviewed-by: Nícolas F. R. A. Prado <nfraprado@...labora.com>

Thanks,
Nícolas