[libcamera-devel] [PATCH 2/2] libcamera: v4l2_device: Add methods to get/set format

[Laurent Pinchart]

Hi Jacopo,

On Wed, Jan 30, 2019 at 03:37:13PM +0100, Jacopo Mondi wrote:
> On Wed, Jan 30, 2019 at 01:10:00PM +0200, Laurent Pinchart wrote:
> > On Mon, Jan 28, 2019 at 04:11:37PM +0100, Jacopo Mondi wrote:
> >> Add methods to set and get the image format programmed on a V4L2Device
> >> for both the single and multi planar use case.
> >>
> >> Signed-off-by: Jacopo Mondi <jacopo at jmondi.org>
> >> ---
> >>  src/libcamera/include/v4l2_device.h |  10 +++
> >>  src/libcamera/v4l2_device.cpp       | 128 ++++++++++++++++++++++++++++
> >>  2 files changed, 138 insertions(+)
> >>
> >> diff --git a/src/libcamera/include/v4l2_device.h b/src/libcamera/include/v4l2_device.h
> >> index c70959e..fe54220 100644
> >> --- a/src/libcamera/include/v4l2_device.h
> >> +++ b/src/libcamera/include/v4l2_device.h
> >> @@ -86,10 +86,20 @@ public:
> >>  	const char *deviceName() const { return caps_.card(); }
> >>  	const char *busName() const { return caps_.bus_info(); }
> >>
> >> +	int format(V4L2DeviceFormat *fmt);
> >
> > As an exception to the general rule, I'd rename format() to getFormat()
> > to follow the V4L2 naming. I won't push hard for this, but I think this
> > was the general preference of the team as well.
> 
> iirc we discussed that and went for this solution. I can re-change it
> in case..

I think I replied to a previous e-mail explaining that I thought an
exception would make sense here, and I recall (possibly incorrectly)
that you were in favour of getFormat(). As I said, I won't push, but if
we all agree getFormat() makes sense, they I think we should go for it.

> >> +	int setFormat(V4L2DeviceFormat *fmt);
> >
> > How about spelling format in full (here and below) for the function
> > parameter ?
> 
> Ok
> 
> >> +
> >>  private:
> >>  	std::string deviceNode_;
> >>  	int fd_;
> >>  	V4L2Capability caps_;
> >> +	enum v4l2_buf_type bufferType_;
> >> +
> >> +	int getFormatSingleplane(V4L2DeviceFormat *fmt);
> >> +	int setFormatSingleplane(V4L2DeviceFormat *fmt);
> >> +
> >> +	int getFormatMultiplane(V4L2DeviceFormat *fmt);
> >> +	int setFormatMultiplane(V4L2DeviceFormat *fmt);
> >>  };
> >>
> >>  } /* namespace libcamera */
> >> diff --git a/src/libcamera/v4l2_device.cpp b/src/libcamera/v4l2_device.cpp
> >> index d6143f2..5c415d0 100644
> >> --- a/src/libcamera/v4l2_device.cpp
> >> +++ b/src/libcamera/v4l2_device.cpp
> >> @@ -227,6 +227,15 @@ int V4L2Device::open()
> >>  		return -EINVAL;
> >>  	}
> >>
> >> +	if (caps_.isCapture())
> >> +		bufferType_ = caps_.isMultiplanar()
> >> +			    ? V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE
> >> +			    : V4L2_BUF_TYPE_VIDEO_CAPTURE;
> >> +	else
> >> +		bufferType_ = caps_.isMultiplanar()
> >> +			    ? V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE
> >> +			    : V4L2_BUF_TYPE_VIDEO_OUTPUT;
> >> +
> >>  	return 0;
> >>  }
> >>
> >> @@ -269,4 +278,123 @@ void V4L2Device::close()
> >>   * \return The string containing the device location
> >>   */
> >>
> >> +/**
> >> + * \brief Retrieve the image format set on the V4L2 device
> >> + * \return 0 for success, a negative error code otherwise
> >
> > s/for/on/
> >
> >> + */
> >> +int V4L2Device::format(V4L2DeviceFormat *fmt)
> >> +{
> >> +	return caps_.isMultiplanar() ? getFormatMultiplane(fmt) :
> >> +				       getFormatSingleplane(fmt);
> >> +}
> >> +
> >> +/**
> >> + * \brief Configure an image format on the V4L2 device
> >> + * \return 0 for success, a negative error code otherwise
> >
> > s/for/on/
> >
> >> + */
> >> +int V4L2Device::setFormat(V4L2DeviceFormat *fmt)
> >> +{
> >> +	return caps_.isMultiplanar() ? setFormatMultiplane(fmt) :
> >> +				       setFormatSingleplane(fmt);
> >> +}
> >> +
> >> +int V4L2Device::getFormatSingleplane(V4L2DeviceFormat *fmt)
> >> +{
> >> +	struct v4l2_format v4l2Fmt;
> >
> > v4l2Format ? Or maybe just fmt if you rename the function parameter to
> > format ?
> 
> Ok
> 
> > You need to initialize v4l2Fmt to 0, that's a requirement of the V4L2
> > API. = {}; will suffice.
> >
> 
> correct.
> 
> >> +	struct v4l2_pix_format *pix = &v4l2Fmt.fmt.pix;
> >> +	int ret;
> >> +
> >> +	v4l2Fmt.type = bufferType_;
> >> +	ret = ioctl(fd_, VIDIOC_S_FMT, &v4l2Fmt);
> >
> > Shouldn't this be VIDIOC_G_FMT ? This outlines a missing test case :-)
> >
> 
> My bad, I'm sorry.
> For a test case, how should we make sure we test all possible use
> cases (planar/multiplanar, capture/output). The device that runs the
> test might not have all of these... Could VIMC or vivid help us here?

I think they could help. I haven't checked which of the
single/multi-planar APIs those drivers use, and whether they could help
testing both, but we could at least test one of the two.

> >> +	if (ret) {
> >> +		ret = -errno;
> >> +		LOG(Error) << "Unable to get format: " << strerror(-ret);
> >> +		return ret;
> >> +	}
> >> +
> >> +	fmt->width = pix->width;
> >> +	fmt->height = pix->height;
> >> +	fmt->fourcc = pix->pixelformat;
> >> +	fmt->planes = 1;
> >> +	fmt->planesFmt[0].bpl = pix->bytesperline;
> >> +	fmt->planesFmt[0].size = pix->sizeimage;
> >> +
> >> +	return 0;
> >> +}
> >> +
> >> +int V4L2Device::setFormatSingleplane(V4L2DeviceFormat *fmt)
> >> +{
> >> +	struct v4l2_format v4l2Fmt;
> >> +	struct v4l2_pix_format *pix = &v4l2Fmt.fmt.pix;
> >> +	int ret;
> >> +
> >> +	v4l2Fmt.type = bufferType_;
> >> +	pix->width = fmt->width;
> >> +	pix->height = fmt->height;
> >> +	pix->pixelformat = fmt->fourcc;
> >
> > How about bytesperline and sizeimage ?
> 
> The description here
> https://www.kernel.org/doc/html/v4.13/media/uapi/v4l/pixfmt-002.html#c.v4l2_pix_format
> quite confused me.
> 
> Particularly: "Size in bytes of the buffer to hold a complete image,
> set by the driver."

You're right about sizeimage. For bytesperline, though, you should pass
it to the ioctl.

> >> +
> >> +	ret = ioctl(fd_, VIDIOC_S_FMT, &v4l2Fmt);
> >> +	if (ret) {
> >> +		ret = -errno;
> >> +		LOG(Error) << "Unable to set format: " << strerror(-ret);
> >> +		return ret;
> >> +	}
> >> +
> >
> > Shouldn't fmt be updated ?
> 
> Good question, what semantic would we want to assign to this
> functions? A setFormat returns an updated format? I here thought to
> clearly separate this: to know what is actually set, you have to call
> g_fmt again. Honestly, now that I re-think this, I am not convinced
> anymore this is the right way, as the V4L2 S_FMT actually returns an
> updated format, so it might be worth updating it here before return.

I think mimicking the VIDIOC_S_FMT semantics would make sense, as it
would save a VIDIOC_G_FMT call for users of this class.

> >> +	return 0;
> >> +}
> >> +
> >> +int V4L2Device::getFormatMultiplane(V4L2DeviceFormat *fmt)
> >
> > The above comments hold for the mplane functions too.
> >
> >> +{
> >> +	struct v4l2_format v4l2Fmt;
> >> +	struct v4l2_pix_format_mplane *pix = &v4l2Fmt.fmt.pix_mp;
> >> +	int ret;
> >> +
> >> +	v4l2Fmt.type = bufferType_;
> >> +	ret = ioctl(fd_, VIDIOC_G_FMT, &v4l2Fmt);
> 
> At least this one is right...

Sometimes copy & paste works ;-)

> >> +	if (ret) {
> >> +		ret = -errno;
> >> +		LOG(Error) << "Unable to get format: " << strerror(-ret);
> >> +		return ret;
> >> +	}
> >> +
> >> +	fmt->width = pix->width;
> >> +	fmt->height = pix->height;
> >> +	fmt->fourcc = pix->pixelformat;
> >> +	fmt->planes = pix->num_planes;
> >> +
> >> +	for (unsigned int i = 0; i < fmt->planes; ++i) {
> >> +		fmt->planesFmt[i].bpl = pix->plane_fmt[i].bytesperline;
> >> +		fmt->planesFmt[i].size = pix->plane_fmt[i].sizeimage;
> >> +	}
> >> +
> >> +	return 0;
> >> +}
> >> +
> >> +int V4L2Device::setFormatMultiplane(V4L2DeviceFormat *fmt)
> >> +{
> >> +	struct v4l2_format v4l2Fmt;
> >> +	struct v4l2_pix_format_mplane *pix = &v4l2Fmt.fmt.pix_mp;
> >> +	int ret;
> >> +
> >> +	v4l2Fmt.type = bufferType_;
> >> +	pix->width = fmt->width;
> >> +	pix->height = fmt->height;
> >> +	pix->pixelformat = fmt->fourcc;
> >> +	pix->num_planes = fmt->planes;
> >> +
> >> +	for (unsigned int i = 0; i < pix->num_planes; ++i) {
> >> +		pix->plane_fmt[i].bytesperline = fmt->planesFmt[i].bpl;
> >> +		pix->plane_fmt[i].sizeimage = fmt->planesFmt[i].size;
> >> +	}
> >> +
> >> +	ret = ioctl(fd_, VIDIOC_S_FMT, &v4l2Fmt);
> >> +	if (ret) {
> >> +		ret = -errno;
> >> +		LOG(Error) << "Unable to set format: " << strerror(-ret);
> >> +		return ret;
> >> +	}
> >> +
> >> +	return 0;
> >> +}
> >> +
> >>  } /* namespace libcamera */

-- 
Regards,

Laurent Pinchart