On Tue, 4 Jul 2023 at 13:38, Jacopo Mondi <jacopo.mondi@xxxxxxxxxxxxxxxx> wrote: > > Document the suggested way to exposure controls for exposure and gain > for camera sensor drivers. > > Signed-off-by: Jacopo Mondi <jacopo.mondi@xxxxxxxxxxxxxxxx> > --- > .../driver-api/media/camera-sensor.rst | 27 +++++++++++++++++++ > 1 file changed, 27 insertions(+) > > diff --git a/Documentation/driver-api/media/camera-sensor.rst b/Documentation/driver-api/media/camera-sensor.rst > index 7516d61a903d..fb70d55f6671 100644 > --- a/Documentation/driver-api/media/camera-sensor.rst > +++ b/Documentation/driver-api/media/camera-sensor.rst > @@ -189,3 +189,30 @@ the ``V4L2_CID_VFLIP`` and ``V4L2_CID_HFLIP`` controls with the > a flip can potentially change the output buffer content layout. Flips should > also be taken into account when enumerating and handling media bus formats > on the camera sensor source pads. > + > +Exposure and Gain Control > +------------------------- > + > +Camera sensor drivers that allow applications to control the image exposure > +and gain should do so by exposing dedicated controls to applications. > + > +Exposure time is controlled by registering the ``V4L2_CID_EXPOSURE`` control. > +The control definition does not specify a unit to allow maximum flexibility > +for multiple device types, but when used for camera sensor drivers it should be > +expressed in unit of lines whenever possible. > + > +To convert lines into units of time, the total line length (visible and > +not visible pixels) has to be divided by the pixel rate:: > + > + line duration = total line length / pixel rate > + = (image width + horizontal blanking) / pixel rate > + > +Camera sensor driver should try whenever possible to distinguish between the > +analogue and digital gain control functions. Analogue gain is a multiplier nit: multiplication factor > +factor applied to all color channels on the pixel array before they get > +converted in the digital domain. It should be made controllable by nit: converted into the digital domain > +registering the ``V4L2_CID_ANALOGUE_GAIN`` control, expressed as a device > +specific gain code. Digital gain control is optional and should be exposed to > +applications by registering ``V4L2_CID_DIGITAL_GAIN``. Camera sensor drivers are > +discouraged from using ``V4L2_CID_GAIN`` as it doesn't allow differentiation of > +analogue vs digital gain. Sorry to have missed those first time around. With or without: Reviewed-by: Dave Stevenson <dave.stevenson@xxxxxxxxxxxxxxx> > -- > 2.40.1 >
