Hi Hans, On Mon, Oct 25, 2021 at 12:47:05PM +0200, Hans Verkuil wrote: > On 25/10/2021 12:30, Laurent Pinchart wrote: > > 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. Interface links are only meant to link entities to interfaces, not entities to entities. media_create_intf_link() is only called for that purpose today. > To my knowledge, this is all available. To my knowledge, it isn't :-) I'd be happy to be proven wrong though. -- Regards, Laurent Pinchart
