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

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Date:   Thu, 22 Feb 2018 14:14:53 +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 Thursday, 22 February 2018 14:04:12 EET jacopo mondi wrote:
> On Wed, Feb 21, 2018 at 10:28:06PM +0200, Laurent Pinchart wrote:
> > 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.
> 
> Ack, we got the same understanding for RGB formats. I wonder if for
> those formats we wouldn't need a V4L2_YCBCR_ENC_NONE or similar...

That, or explicitly documenting that when the format is not YUV the field 
should be set by both drivers and applications to V4L2_YCBCR_ENC_DEFAULT when 
written and ignored when read.

> > 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.
> 
> In YUYV mode, I see values > 0xf0 ( > 240, which is the max value for
> CbCr samples in limited quantization range), so I assume quantization
> is full range.

It should be, yes. What's the minimum and maximum values you get ?

> Actually the hardest part here was having a white enough surface to
> point the sensor to :)

Pointing a flashlight to the sensor usually does the trick.

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

-- 
Regards,

Laurent Pinchart