Re: [PATCH v4] usb: gadget: uvc: fix multiple opens

[Michael Tretter <m.tretter@pengutronix.de>]

On Fri, 15 Jan 2021 15:09:39 +0200, Felipe Balbi wrote:
> Thomas Haemmerle <thomas.haemmerle@wolfvision.net> writes:
> > Currently, the UVC function is activated when open on the corresponding
> > v4l2 device is called.
> > On another open the activation of the function fails since the
> > deactivation counter in `usb_function_activate` equals 0. However the
> > error is not returned to userspace since the open of the v4l2 device is
> > successful.
> >
> > On a close the function is deactivated (since deactivation counter still
> > equals 0) and the video is disabled in `uvc_v4l2_release`, although the
> > UVC application potentially is streaming.
> >
> > Move activation of UVC function to subscription on UVC_EVENT_SETUP
> > because there we can guarantee for a userspace application utilizing
> > UVC.
> > Block subscription on UVC_EVENT_SETUP while another application already
> > is subscribed to it, indicated by `bool func_connected` in
> > `struct uvc_device`.
> > Extend the `struct uvc_file_handle` with member `bool is_uvc_app_handle`
> > to tag it as the handle used by the userspace UVC application.
> >
> > With this a process is able to check capabilities of the v4l2 device
> > without deactivating the function for the actual UVC application.
> >
> > Signed-off-by: Thomas Haemmerle <thomas.haemmerle@wolfvision.net>
> 
> Laurent, do you agree with the change?

Gentle ping.

Michael