linux-kernel - Re: [PATCHv3 1/1 RESEND] media: imx: Round line size to 4 bytes

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Date:   Tue, 1 Nov 2022 13:38:34 +0100
From:   Dorota Czaplejewicz <dorota.czaplejewicz@...i.sm>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Steve Longerbeam <slongerbeam@...il.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        linux-media@...r.kernel.org, linux-staging@...ts.linux.dev,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kernel@...i.sm, phone-devel@...r.kernel.org
Subject: Re: [PATCHv3 1/1 RESEND] media: imx: Round line size to 4 bytes

Hi all,

On Mon, 17 Oct 2022 16:30:59 +0200
Dorota Czaplejewicz <dorota.czaplejewicz@...i.sm> wrote:

> Hi,
> 
> On Mon, 17 Oct 2022 11:28:57 +0300
> Laurent Pinchart <laurent.pinchart@...asonboard.com> wrote:
> 

[snip]

> > I would also very much appreciate feedback from NXP on this. There's a
> > risk of ill side-effects that I would prefer ruling out very clearly.  
> 
> I posted a question on the NXP forum: https://community.nxp.com/t5/i-MX-Processors/i-MX8MQ-CSI-line-size-constraint-documentation-mistake/m-p/1538629#M196448
> 

This question received a reply from NXP today: https://community.nxp.com/t5/i-MX-Processors/i-MX8MQ-CSI-line-size-constraint-documentation-mistake/m-p/1546872/highlight/true#M197067

Quoting NXP's answer:

> Do I understand correctly, that streams divisible by 4×4 will work on other i.MX8 hardware too? - Yes
> Will those kind of resolutions work on i.MX7 series CSI hardware? - Yes

which implies no bad side effects the way I read it. Is this sufficient for the kernel?

Cheers,
Dorota

> >   
> > > Signed-off-by: Dorota Czaplejewicz <dorota.czaplejewicz@...i.sm>
> > > ---
> > > Hello,
> > > 
> > > the Librem 5 is using an out-of-tree driver for s5k3l6xx, and rounding to 4 is optimal to operate it.
> > > 
> > > This revision improves the commit message.
> > > 
> > > Cheers,
> > > Dorota Czaplejewicz
> > > 
> > >  drivers/staging/media/imx/imx7-media-csi.c | 4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/drivers/staging/media/imx/imx7-media-csi.c b/drivers/staging/media/imx/imx7-media-csi.c
> > > index a0553c24cce4..af821b410c3f 100644
> > > --- a/drivers/staging/media/imx/imx7-media-csi.c
> > > +++ b/drivers/staging/media/imx/imx7-media-csi.c
> > > @@ -999,10 +999,10 @@ static int imx7_csi_mbus_fmt_to_pix_fmt(struct v4l2_pix_format *pix,
> > >  	}
> > >  
> > >  	/* Round up width for minimum burst size */
> > > -	width = round_up(mbus->width, 8);
> > > +	width = round_up(mbus->width, 4);
> > >  
> > >  	/* Round up stride for IDMAC line start address alignment */
> > > -	stride = round_up((width * cc->bpp) >> 3, 8);
> > > +	stride = round_up((width * cc->bpp) >> 3, 4);
> > >  
> > >  	pix->width = width;
> > >  	pix->height = mbus->height;    
> >   
> 


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