linux-kernel - Re: [PATCH v9 11/11] media: i2c: ov7670: Fully set mbus frame fmt

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Message-ID: <56271779.hLAmkO6BAC@avalon>
Date:   Wed, 21 Feb 2018 22:28:06 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     jacopo mondi <jacopo@...ndi.org>
Cc:     Jacopo Mondi <jacopo+renesas@...ndi.org>, magnus.damm@...il.com,
        geert@...der.be, hverkuil@...all.nl, mchehab@...nel.org,
        festevam@...il.com, sakari.ailus@....fi, robh+dt@...nel.org,
        mark.rutland@....com, pombredanne@...b.com,
        linux-renesas-soc@...r.kernel.org, linux-media@...r.kernel.org,
        linux-sh@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v9 11/11] media: i2c: ov7670: Fully set mbus frame fmt

Hi Jacopo,

On Tuesday, 20 February 2018 10:58:57 EET jacopo mondi wrote:
> On Mon, Feb 19, 2018 at 09:19:32PM +0200, Laurent Pinchart wrote:
> > On Monday, 19 February 2018 18:59:44 EET Jacopo Mondi wrote:
> >> The sensor driver sets mbus format colorspace information and sizes,
> >> but not ycbcr encoding, quantization and xfer function. When supplied
> >> with an badly initialized mbus frame format structure, those fields
> >> need to be set explicitly not to leave them uninitialized. This is
> >> tested by v4l2-compliance, which supplies a mbus format description
> >> structure and checks for all fields to be properly set.
> >> 
> >> Without this commit, v4l2-compliance fails when testing formats with:
> >> fail: v4l2-test-formats.cpp(335): ycbcr_enc >= 0xff
> >> 
> >> Signed-off-by: Jacopo Mondi <jacopo+renesas@...ndi.org>
> >> ---
> >> 
> >>  drivers/media/i2c/ov7670.c | 4 ++++
> >>  1 file changed, 4 insertions(+)
> >> 
> >> diff --git a/drivers/media/i2c/ov7670.c b/drivers/media/i2c/ov7670.c
> >> index 25b26d4..61c472e 100644
> >> --- a/drivers/media/i2c/ov7670.c
> >> +++ b/drivers/media/i2c/ov7670.c
> >> @@ -996,6 +996,10 @@ static int ov7670_try_fmt_internal(struct
> >> v4l2_subdev
> >> *sd, fmt->height = wsize->height;
> >> 
> >>  	fmt->colorspace = ov7670_formats[index].colorspace;
> > 
> > On a side note, if I'm not mistaken the colorspace field is set to SRGB
> > for all entries. Shouldn't you hardcode it here and remove the field ?
> > 
> >> +	fmt->ycbcr_enc = V4L2_YCBCR_ENC_DEFAULT;
> >> +	fmt->quantization = V4L2_QUANTIZATION_DEFAULT;
> >> +	fmt->xfer_func = V4L2_XFER_FUNC_DEFAULT;
> > 
> > How about setting the values explicitly instead of relying on defaults ?
> > That would be V4L2_YCBCR_ENC_601, V4L2_QUANTIZATION_LIM_RANGE and
> > V4L2_XFER_FUNC_SRGB. And could you then check a captured frame to see if
> > the sensor outputs limited or full range ?
> 
> This actually makes me wonder if those informations (ycbcb_enc,
> quantization and xfer_func) shouldn't actually be part of the
> supported format list... I blindly added those default fields in the
> try_fmt function, but I doubt they applies to all supported formats.
> 
> Eg. the sensor supports YUYV as well as 2 RGB encodings (RGB444 and
> RGB 565) and 1 raw format (BGGR). I now have a question here:
> 
> 1) ycbcr_enc transforms non-linear R'G'B' to Y'CbCr: does this
> applies to RGB and raw formats? I don't think so, and what value is
> the correct one for the ycbcr_enc field in this case? I assume
> xfer_func and quantization applies to all formats instead..

There's no encoding for RGB formats if I understand things correctly, so I'd 
set ycbcr_enc to V4L2_YCBCR_ENC_DEFAULT. The transfer function and the 
quantization apply to all formats, but I'd be surprised to find a sensor 
outputting limited range for RGB.

Have you been able to check whether the sensor outputs limited range of full 
range YUV ? If it outputs full range you can hardcode quantization to 
V4L2_QUANTIZATION_FULL_RANGE for all formats.

> >>  	info->format = *fmt;
> >>  	
> >>  	return 0;

-- 
Regards,

Laurent Pinchart