Re: [PATCH v2 0/6] media: uvcvideo: Implement the Privacy GPIO as a subdevice

Hans de Goede
2024-11-11T14:35:19Z

p.s.

On 11-Nov-24 1:59 PM, Hans de Goede wrote:
> Hi Ricardo, Et al.,
>
> On 8-Nov-24 9:25 PM, Ricardo Ribalda wrote:
>> Some notebooks have a button to disable the camera (not to be mistaken
>> with the mechanical cover). This is a standard GPIO linked to the
>> camera via the ACPI table.
>>
>> 4 years ago we added support for this button in UVC via the Privacy control.
>> This has two issues:
>> - If the camera has its own privacy control, it will be masked
>> - We need to power-up the camera to read the privacy control gpio.
>
> Thinking more about this I think we need to start with looking at the userspace
> API for privacy controls, define how we want that to look and then go from
> there.
>
> The reason I'm writing this is because due to my work in drivers/platform/x86
> (pdx86) on EC / ACPI / WMI drivers for non chromebooks I am aware of at least
> 4 different methods camera on/off (aka privacy) toggles are being reported
> to userspace at the moment. Adding a v4l2-ctrl on a subdev instead of directly
> on /dev/video# would be adding a 5th method which seems highly undesirable.
>
> Instead I would like to first focus on fixing these userspace API
> inconsistencies agreeing on a single API we want to use everywhere
> going forward. We don't need to fix all drivers at once, but IMHO we
> should agree on what the API should look like and document that and
> any future drivers implementing camera privacy control related code
> then must use the new API.
>
> Lets start with the 3 APIs I'm currently aware of:
>
> 1. uvcvideo driver exporting V4L2_CID_PRIVACY on /dev/video#
> uvcvideo seems to be the only user of this CID (i)
>
> 2. pdx86 drivers exporting an input evdev with EV_SW,
> SW_CAMERA_LENS_COVER. This is somewhat of a special case
> for some Dell laptops with an electro-mechanical shutter
> operated by the EC. But this is not also used by
> hp-wmi.c where it does not necessarily indicate the

s/not/now/

> status of a mechanical cover, but also possibly simply
> disconnecting the camera from the USB bus.
>
> 3. pdx86 drivers exporting an input evdev with EV_KEY,
> KEY_CAMERA_ACCESS_ENABLE, KEY_CAMERA_ACCESS_DISABLE
> These KEY codes are based on offical the HUTRR72 HID/HUT
> extension and as such may also be send by USB/I2C/BT HID
> devices.
>
> The only user outside of hid-input.c is the recently added
> drivers/platform/x86/lenovo-wmi-camera.c driver and I'm
> wondering if that should not use SW_CAMERA_LENS_COVER
> instead. I'll ask the driver author about how this

I have send an email out about possibly switching this to
SW_CAMERA_LENS_COVER :

https://lore.kernel.org/platform-driver-x86/5666914c-e8c2-481d-8fdf-aff82865c228@redhat.com/

Regards,

Hans

> 4. pdx86 drivers exporting an input evdev with EV_KEY,
> KEY_CAMERA. Note this 4th method lacks information on if
> the camera was enabled or disabled. In many cases this
> is send to indicate that the EC has either dropped
> a UVC camera of the bus, or added it to the bus.
> Ideally we would have some helper checking for internal
> UVC camera presence and turn this into 2 or 3.
>
> TL;DR: it a mess.
>
> Circling back to this patch-set, note how 3 of the 4
> currently in use variants today use in input evdev.
>
> I think that using an input evdev (shared with the
> snapshot button if present) will give us a nice out for
> the power-management issue with the V4L2_CID_PRIVACY,
> while at the same time giving a nice opportunity to
> standardize on a single userspace API.
>
> My proposal would be to standardize on SW_CAMERA_LENS_COVER
> I realize that the GPIO does not always indicate a lens
> cover, but the resulting black frames are the same result
> as if there were a lens cover and looking at:
>
> https://support.hp.com/ie-en/document/ish_3960099-3335046-16
>
> and then the second picture when expanding "Locate and use
> the webcam privacy switch" that does look like it may be
> an actual cover which reports back its state through a GPIO.
>
> The reason why I'm not in favor of using
> KEY_CAMERA_ACCESS_ENABLE + KEY_CAMERA_ACCESS_DISABLE is that
> looking at the HUTRR72 it talks about:
> "Enables programmatic access to camera device"
> which suggests that it is a request to the OS / desktop-
> environment to block camera access at the software level,
> rather then reporting back that a hw-level block is in place.
>
> And since these may be used by any HID device we are not of
> control in how these will be used.
>
> Ricardo, what do you think of instead of using a v4l-subdev,
> using an input evdev (shared with the existing one) reporting
> SW_CAMERA_LENS_COVER ? The v4l-subdev approach will need
> userspace changes anyways and if we are going to make userspace
> changes we might as well use the best API available.
>
> One downside of going the evdev route is that it is a bit
> harder for userspace to map the evdev to a camera:
>
> 1. For the various WMI interfaces this already is impossible,
> and just to show a notification it is not necessary (using
> an external cam will make things weird though).
>
> 2. For UVC cameras mapping the evdev to the /dev/video#
> node can still be done by looking if they share a parent
> USB interface. This is e.g. already done in apps like
> xawtv looking at the PCI parent to pair up /dev/video#
> for video capture with the ALSA interface exposed for
> sound by bttv cards.
>
> 3. We can maybe do something at the media-controller
> level to help userspace linking a camera to its evdev node.
> This would also be helpful for the existing WMI interfaces.
>
> Regards,
>
> Hans
>
>
>
> i) With the exception of drivers/media/pci/intel/ivsc/mei_csi.c
> which has a V4L2_CID_PRIVACY control which always reads 0, so
> I guess we can / should probably drop that.
>
>
>
> p.s.
>
> I do plan to also get back to you on the actually powermanagement
> discussion. But only so many hours in a day, so it will probably
> be a couple of days.
>
>