On 25/10/2021 12:30, Laurent Pinchart wrote: > Hi Hans, > > On Mon, Oct 25, 2021 at 12:06:30PM +0200, 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. > > The second approach is what V4L2 does already. We have a set of drivers > for VCMs already (search for V4L2_CID_FOCUS_ABSOLUTE in > drivers/media/i2c/). > >> 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 ? > > The information was initially envisioned to be conveyed to userspace > through the media controller API, using the entity group ID to group the > camera sensor, lens controller and flash controller, but the > media_entity_desc.group_id field is now obsolete. No other mechanism > exist to replace that as far as I know, so we'll have to create > something. There have been some talks about using a special kind of link > to expose the relationship between the camera sensor and other > components. > I thought this was implemented: there should be an interface link from the sensor entity to the subdev for the flash or focus control. To my knowledge, this is all available. Regards, Hans
