Re: [PATCH v3 0/8] media: uvcvideo: Implement the Privacy GPIO as a evdev

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

On Tue, Nov 26, 2024 at 06:12:46PM +0100, Ricardo Ribalda wrote:
> On Tue, 26 Nov 2024 at 17:51, Laurent Pinchart wrote:
> > On Tue, Nov 26, 2024 at 05:27:57PM +0100, Ricardo Ribalda wrote:
> > > On Mon, 25 Nov 2024 at 22:35, Laurent Pinchart wrote:
> > > > On Mon, Nov 25, 2024 at 03:41:19PM +0100, Hans de Goede wrote:
> > > > > On 25-Nov-24 2:14 PM, Laurent Pinchart wrote:
> > > > > > On Mon, Nov 25, 2024 at 01:01:14PM +0100, Hans de Goede wrote:
> > > > > >> On 18-Nov-24 5:47 PM, Ricardo Ribalda wrote:
> > > > > >>> On Mon, 18 Nov 2024 at 16:43, Hans de Goede wrote:
> > > > > >>>> On 15-Nov-24 9:20 AM, Ricardo Ribalda wrote:
> > > > > >>>>> On Fri, 15 Nov 2024 at 00:06, Laurent Pinchart wrote:
> > > > >
> > > > > <snip>
> > > > >
> > > > > >>>>>> Is there any ACPI- or WMI-provided information that could assist with
> > > > > >>>>>> associating a privacy GPIO with a camera ?
> > > > > >>
> > > > > >> I just realized I did not answer this question from Laurent
> > > > > >> in my previous reply.
> > > > > >>
> > > > > >> No unfortunately there is no ACPI- or WMI-provided information that
> > > > > >> could assist with associating ACPI/WMI camera privacy controls with
> > > > > >> a specific camera. Note that these are typically not exposed as a GPIO,
> > > > > >> but rather as some vendor firmware interface.
> > > > > >>
> > > > > >> Thinking more about this I'm starting to believe more and more
> > > > > >> that the privacy-control stuff should be handled by libcamera
> > > > > >> and then specifically by the pipeline-handler, with some helper
> > > > > >> code to share functionality where possible.
> > > > > >>
> > > > > >> E.g. on IPU6 equipped Windows laptops there may be some ACPI/WMI
> > > > > >> driver which provides a /dev/input/event# SW_CAMERA_LENS_COVER node.
> > > > > >
> > > > > > Using an event device means that the user would need permissions to
> > > > > > access it. Would distributions be able to tell the device apart from
> > > > > > other event devices such as mouse/keyboard, where a logged user may not
> > > > > > have permission to access all event devices in a multi-seat system ?
> > > > >
> > > > > input events modaliases contain a lot of info, including what sort
> > > > > of events they report, e.g. :
> > > > >
> > > > > [hans@shalem uvc]$ cat /sys/class/input/input36/modalias
> > > > > input:b0003v046Dp405Ee0111-e0,1,2,3,4,11,14,k71,72,73,74,75,77,78,79,7A,7B,7C,7D,7E,7F,80,81,82,83,84,85,86,87,88,89,8A,8B,8C,8E,8F,90,96,98,9B,9C,9E,9F,A1,A3,A4,A5,A6,A7,A8,A9,AB,AC,AD,AE,B0,B1,B2,B3,B4,B5,B6,B7,B8,B9,BA,BB,BC,BD,BE,BF,C0,C1,C2,CC,CE,CF,D0,D1,D2,D4,D8,D9,DB,DF,E0,E1,E4,E5,E6,E7,E8,E9,EA,EB,F0,F1,F4,100,110,111,112,113,114,115,116,117,118,119,11A,11B,11C,11D,11E,11F,161,162,166,16A,16E,172,174,176,177,178,179,17A,17B,17C,17D,17F,180,182,183,185,188,189,18C,18D,18E,18F,190,191,192,193,195,197,198,199,19A,19C,1A0,1A1,1A2,1A3,1A4,1A5,1A6,1A7,1A8,1A9,1AA,1AB,1AC,1AD,1AE,1AF,1B0,1B1,1B7,1BA,240,241,242,243,244,245,246,247,248,249,24A,24B,24C,24D,250,251,260,261,262,263,264,265,r0,1,6,8,B,C,a20,m4,l0,1,2,3,4,sfw
> > > > >
> > > > > So I believe that we can create a udev rule which matches on input
> > > > > devices with SW_CAMERA_LENS_COVER functionality and set a uaccess
> > > > > tag on those just like it is done for /dev/video# nodes.
> > > > >
> > > > > Or we can just use a specific input-device-name (sub) string
> > > > > and match on that.
> > > > >
> > > > > This may require using a separate input_device with just
> > > > > the SW_CAMERA_LENS_COVER functionality in some of the laptop
> > > > > ACPI / WMI drivers, but that is an acceptable compromise IMHO.
> > > >
> > > > As long as it's doable I'm OK with it.
> > > >
> > > > > (we don't want to report privacy sensitive input events on
> > > > > these nodes to avoid keylogging).
> > > > >
> > > > > > Would compositors be able to ignore the device to let libcamera handle
> > > > > > it ?
> > > > >
> > > > > input devices can be opened multiple times and we want the compositor
> > > > > to also open it to show camera on/off OSD icons / messages.
> > > >
> > > > I'm not sure we want that though, as the event should be associated with
> > > > a particular camera in messages. It would be better if it still went
> > > > through libcamera and pipewire.
> > >
> > > For OSD we do not necessarily need to know what camera the GPIO is
> > > associated with.
> > >
> > > We just want to give instant feedback about a button on their device.
> > > Eg in ChromeOS we just say: "camera off" not "user facing camera off"
> >
> > That may be true of Chrome OS, but in general, other systems may want to
> > provide more detailed information. I wouldn't model the API and
> > architecture just on Chrome OS.
> 
> It is not about ChromeOS, it is about the use case.
> 
> We were talking about 2 usecases:
> - instant feedback for a button. Actor: OSD / composer
> - this camera is disabled, please use other camera or enable it: Actor
> camera app, or camera "service" (read pipewire, libcamera, or the
> permission handler for snap)
> 
> There are some examples showing that for "instant feedback" there is
> no need to link the event to the camera:
> - there is hardware where this is not possible to establish the link.
> - ChromeOS does not show the camera name (when it has enough
> information to do so)
> - I believe Hans mentioned that Windows does not show the camera name.
> - (Hans, are you wiring SW_CAMERA_LENS_COVER to the user right now?)
> Do you know of a system where this info is needed?
> 
> My problem is that I do not see where libcamera fits for the "instant
> feedback" usecase:
> - libcamera will be running as a service and telling the UI that the
> camera is disabled? how will it communicate with the OS?

Not libcamera itself, but a camera service on top of it. For typical
desktop cases, that would be pipewire. I don't know how it communicates
with other actors, that's not my area of expertise, but I would be
surprised if it wouldn't be able to.

> - the OS will run a "libcamera helper" every second to get the switch
> status for every camera?
> - the OS will wait for an input event and run a "libcamera helper" to
> find the correlation with the camera?
> 
> I think it is simpler that the OS just waits for an
> SW_CAMERA_LENS_COVER event and display "camera off". The same way it
> waits for "caps lock" today
> 
> In any case:
> -  for uvc, it seems like it is easy to go from evdev to videodev (and
> the other way around). Check my previous email
> - udev seems to have a lot of information about the evdev to configure
> the permissions in a way that cover most (all?) of the
> usecases/architectures
> 
> > > > > If opened multiple times all listeners will get the events.
> > > > >
> > > > > >>>>>> We could include the evdev in the MC graph. That will of course only be
> > > > > >>>>>> possible if the kernel knows about that association in the first place.
> > > > > >>>>>> At least the 1st category of devices would benefit from this.
> > > > > >>>>
> > > > > >>>> Yes I was thinking about adding a link to the MC graph for this too.
> > > > > >>>>
> > > > > >>>> Ricardo I notice that in this v3 series you still create a v4l2-subdev
> > > > > >>>> for the GPIO handling and then add an ancillary link for the GPIO subdev
> > > > > >>>> to the mc-graph. But I'm not sure how that is helpful. Userspace would
> > > > > >>>> still need to do parent matching, but then match the evdev parent to
> > > > > >>>> the subdev after getting the subdev from the mc. In that case it might
> > > > > >>>> as well look at the physical (USB-interface) parent of the MC/video
> > > > > >>>> node and do parent matching on that avoiding the need to go through
> > > > > >>>> the MC at all.
> > > > > >>>>
> > > > > >>>> I think using the MC could still be useful by adding a new type of
> > > > > >>>> ancillary link to the MC API which provides a file-path as info to
> > > > > >>>> userspace rather then a mc-link and then just directly provide
> > > > > >>>> the /dev/input/event# path through this new API?
> > > > > >
> > > > > > I don't think we need that. MC can model any type of entity and report
> > > > > > the device major:minor. That plus ancillary links should give us most of
> > > > > > what we need, the only required addition should be a new MC entity
> > > > > > function.
> > > > >
> > > > > Ah interesting yes that should work nicely.

-- 
Regards,

Laurent Pinchart