[libcamera-devel] [PATCH 2/6] libcamera: v4l2_device: Add setControl function

[Jacopo Mondi]

Hi Laurent,

On Mon, Jan 21, 2019 at 10:42:28PM +0200, Laurent Pinchart wrote:
> Hi Jacopo,
>
> Thank you for the patch.

You know, I had this patch around and I will soon need that to set a
single int control on IPU3. For the moment, I would ditch this one and
do it right later.

I'll take your suggestions into account.

Thanks
  j

>
> On Mon, Jan 21, 2019 at 06:27:01PM +0100, Jacopo Mondi wrote:
> > Add function to set controls on a V4L2Device object.
> >
> > Signed-off-by: Jacopo Mondi <jacopo at jmondi.org>
> > ---
> >  src/libcamera/include/v4l2_device.h |  2 ++
> >  src/libcamera/v4l2_device.cpp       | 38 +++++++++++++++++++++++++++++
> >  2 files changed, 40 insertions(+)
> >
> > diff --git a/src/libcamera/include/v4l2_device.h b/src/libcamera/include/v4l2_device.h
> > index c6f3d9a..2787847 100644
> > --- a/src/libcamera/include/v4l2_device.h
> > +++ b/src/libcamera/include/v4l2_device.h
> > @@ -51,6 +51,8 @@ public:
> >  	const char *deviceName() const { return caps_.card(); }
> >  	const char *busName() const { return caps_.bus_info(); }
> >
> > +	int setControl(unsigned int control, int value);
> > +
>
> I think this is needed, but requires a little more thoughts to define a
> good API. To start with, not all controls have integer values, we also
> have string controls. Furthermore, we will also likely need to use the
> extended controls API to set multiple controls at a time, requiring a
> vector to be passed to the function.
>
> Here's a very preliminary proposal.
>
> class V4L2ControlValue
> {
> 	enum Type {
> 		/* The control types. */
> 	};
>
> 	/*
> 	 * This should store the type and value, with appropriate
> 	 * constructors and accessors.
> 	 /
> };
>
> 	int setControl(unsigned int id, const V4L2ControlValue &control);
> 	int setControls(const std::vector<std::pair<unsigned int, V4L2ControlValue>> &controls);
>
> setControl() could be implemented by calling setControls().
> setControls() should use the extended controls API, and possibly fall
> back to the old controls API if the extended API isn't available,
> although I think we can depend on the extended API in libcamera.
>
> We could also create a class that groups together the id and value,
> possibly named V4L2Control, but I have a feeling we will later need to
> enumerate controls and store the data queried from the kernel, and
> V4L2Control would be a good class name for that.
>
> >  private:
> >  	std::string devnode_;
> >  	int fd_;
> > diff --git a/src/libcamera/v4l2_device.cpp b/src/libcamera/v4l2_device.cpp
> > index 59a1ad9..aef0996 100644
> > --- a/src/libcamera/v4l2_device.cpp
> > +++ b/src/libcamera/v4l2_device.cpp
> > @@ -195,4 +195,42 @@ void V4L2Device::close()
> >   * \return The string containing the device location
> >   */
> >
> > +/**
> > + * \brief Set a control value
> > + * \param control The control identifier
> > + * \param value The new control value
> > + *
> > + * Set a user control to the requested value. The function returns the
> > + * new value actually assigned to the control, which might be different
> > + * from the requested \a value one.
> > + *
> > + * \return The new control's value for success, or a negative error code otherwise
> > + */
> > +int V4L2Device::setControl(unsigned int control, int value)
> > +{
> > +	struct v4l2_control v4l2_ctrl = {
> > +		.id = control,
> > +		.value = value,
> > +	};
> > +
> > +	int ret = ioctl(fd_, VIDIOC_S_CTRL, &v4l2_ctrl);
> > +	if (ret) {
> > +		ret = -errno;
> > +		LOG(Error) << "Failed to set control: " << strerror(-ret);
> > +		return ret;
> > +	}
> > +
> > +	v4l2_ctrl = { };
> > +	v4l2_ctrl.id = control;
> > +
> > +	ret = ioctl(fd_, VIDIOC_G_CTRL, &v4l2_ctrl);
> > +	if (ret) {
> > +		ret = -errno;
> > +		LOG(Error) << "Failed to get control: " << strerror(-ret);
> > +		return ret;
> > +	}
> > +
> > +	return v4l2_ctrl.value;
> > +}
> > +
> >  } /* namespace libcamera */
>
> --
> Regards,
>
> Laurent Pinchart
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