On 25/10/2021 12:06, Hans de Goede wrote: > Hi All, > > With my (and Dan's) kernel patch-series to enable the back camera on > the Surface Go shaping up (and hopefully going upstream soon), > the next step is to enable control of the focus lens for the back > camera. > > The focus is controlled through a separate i2c-client which is > described by a 2nd I2cSerialBusV2 resource entry in the ACPI > device for the ov8865 sensor. By default the kernel only instantiates > an i2c-client for the first I2cSerialBusV2 resource entry for an > ACPI device, getting an i2c-client for the 2nd one is easy and > out of scope for this discussion. > > The question which I have is, assuming we have the 2nd i2c-client > instantiated and we have a i2c-driver binding to it, how do we > represent the focus control to userspace. > > I see 2 possible directions we can go here: > > 1. Somehow inject an extra v4l2ctrl for this into the v4l2ctrl > list of the sensor. AFAIK we don't have infra for this atm, but > we could add some generic mechanism to do this to the v4l2-ctrls > core. IMHO from a userspace pov this is the cleanest, but at the > cost of some extra work / possible ugliness on the kernel side. > > 2. Register a separate v4l2_subdev for the focus-ctrl and in > some way provide information to userspace to which sensor this > belongs. > > I believe that both are valid approaches. So before diving into > this I wonder what others are thinking about this. > > Specific questions: > > 1. Hans Verkuil, what do you think about adding > support for another driver to inject ctrls into the ctrl > list of another v4l2(sub)dev ? Maybe something like this > already exists ? If not do you think this is feasible > and desirable to add ? > > 2. If we go with a separate v4l2_subdev, how do we communicate > to which sensor the focus-control belongs to userspace ? What is the bridge driver that controls the sensor? I would need to know a bit more about the architecture. Is it MC-centric? Or is everything controlled through a video device? In the latter case you want the video device to inherit the controls of the sensor and the focus sub-devices, that's supported by the control framework. In the MC-centric case you probably want to have libcamera support that can tie the focus subdev and the sensor subdev together. v4l2_async_nf_parse_fwnode_sensor() supports linking LEDs or lens-focus devices together with the sensor, so that's how a focus device can be associated with a sensor at the ACPI/DT level. So support for 2) is already available. A separate subdev is in my view certainly the correct approach. Regards, Hans
