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

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Date:   Mon, 17 Oct 2022 16:30:59 +0200
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,

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

> Hi Dorota,
> 
> Thank you for the patch.
> 
> On Sun, Oct 16, 2022 at 04:39:28PM +0200, Dorota Czaplejewicz wrote:
> > Section 13.7.6.13 "CSI Image Parameter Register" of the
> > i.MX 8M Quad Applications Processors Reference Manual
> > states that the line size should be divisible by 8 bytes.
> > However, the hardware also accepts sizes divisible by 4 bytes,
> > which are needed to fully utilize the S5K3L6XX sensors.
> > 
> > This patch accepts line sizes divisible by 4 bytes.  
> 
> The patch itself looks fine, but I always worry when we depart from the
> documentation (sometimes that's a worry about documentation inaccuracies
> :-)). In this particular case, we need to test the change on i.MX7 too,
> as the alignment constraints could be platform-specific.
> 
I don't have access to any i.MX7 hardware, unfortunately. I can help anyone who does and wants to test this.

> 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

--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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