linux-kernel - Re: [PATCH] drm/msm: update the high bitfield of certain DSI registers

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Message-ID: <nxayk52mhisyipdsbf5rykuynpg45mk5y5ykqxh76vzyxb6exy@h3qwqdgviumb>
Date: Wed, 30 Jul 2025 16:08:03 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Cc: Ayushi Makhija <quic_amakhija@...cinc.com>, linux-arm-msm@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, robdclark@...il.com, lumag@...nel.org,
        sean@...rly.run, marijn.suijten@...ainline.org, airlied@...il.com,
        simona@...ll.ch, quic_rajeevny@...cinc.com, quic_vproddut@...cinc.com,
        quic_jesszhan@...cinc.com
Subject: Re: [PATCH] drm/msm: update the high bitfield of certain DSI
 registers

On Wed, Jul 30, 2025 at 02:45:13PM +0200, Konrad Dybcio wrote:
> On 7/30/25 2:39 PM, Ayushi Makhija wrote:
> > Currently, the high bitfield of certain DSI registers
> > do not align with the configuration of the SWI registers
> > description. This can lead to wrong programming these DSI
> > registers, for example for 4k resloution where H_TOTAL is
> > taking 13 bits but software is programming only 12 bits
> > because of the incorrect bitmask for H_TOTAL bitfeild,
> > this is causing DSI FIFO errors. To resolve this issue,
> > increase the high bitfield of the DSI registers from 12 bits
> > to 16 bits in dsi.xml to match the SWI register configuration.
> > 
> > Signed-off-by: Ayushi Makhija <quic_amakhija@...cinc.com>
> > ---
> >  drivers/gpu/drm/msm/registers/display/dsi.xml | 28 +++++++++----------
> >  1 file changed, 14 insertions(+), 14 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/msm/registers/display/dsi.xml b/drivers/gpu/drm/msm/registers/display/dsi.xml
> > index 501ffc585a9f..c7a7b633d747 100644
> > --- a/drivers/gpu/drm/msm/registers/display/dsi.xml
> > +++ b/drivers/gpu/drm/msm/registers/display/dsi.xml
> > @@ -159,28 +159,28 @@ xsi:schemaLocation="https://gitlab.freedesktop.org/freedreno/ rules-fd.xsd">
> >  		<bitfield name="RGB_SWAP" low="12" high="14" type="dsi_rgb_swap"/>
> >  	</reg32>
> >  	<reg32 offset="0x00020" name="ACTIVE_H">
> > -		<bitfield name="START" low="0" high="11" type="uint"/>
> > -		<bitfield name="END" low="16" high="27" type="uint"/>
> > +		<bitfield name="START" low="0" high="15" type="uint"/>
> > +		<bitfield name="END" low="16" high="31" type="uint"/>
> >  	</reg32>
> >  	<reg32 offset="0x00024" name="ACTIVE_V">
> > -		<bitfield name="START" low="0" high="11" type="uint"/>
> > -		<bitfield name="END" low="16" high="27" type="uint"/>
> > +		<bitfield name="START" low="0" high="15" type="uint"/>
> > +		<bitfield name="END" low="16" high="31" type="uint"/>
> >  	</reg32>
> >  	<reg32 offset="0x00028" name="TOTAL">
> > -		<bitfield name="H_TOTAL" low="0" high="11" type="uint"/>
> > -		<bitfield name="V_TOTAL" low="16" high="27" type="uint"/>
> > +		<bitfield name="H_TOTAL" low="0" high="15" type="uint"/>
> > +		<bitfield name="V_TOTAL" low="16" high="31" type="uint"/>
> >  	</reg32>
> >  	<reg32 offset="0x0002c" name="ACTIVE_HSYNC">
> > -		<bitfield name="START" low="0" high="11" type="uint"/>
> > -		<bitfield name="END" low="16" high="27" type="uint"/>
> > +		<bitfield name="START" low="0" high="15" type="uint"/>
> > +		<bitfield name="END" low="16" high="31" type="uint"/>
> >  	</reg32>
> >  	<reg32 offset="0x00030" name="ACTIVE_VSYNC_HPOS">
> > -		<bitfield name="START" low="0" high="11" type="uint"/>
> > -		<bitfield name="END" low="16" high="27" type="uint"/>
> > +		<bitfield name="START" low="0" high="15" type="uint"/>
> > +		<bitfield name="END" low="16" high="31" type="uint"/>
> >  	</reg32>
> >  	<reg32 offset="0x00034" name="ACTIVE_VSYNC_VPOS">
> 
> FWIW looks like at least on 8280, ACTIVE_VSYNC_HPOS offset = 0x38
> and HPOS doesn't exist

All registers here are shifted by 0x4 for historical and practical
reasons.

-- 
With best wishes
Dmitry