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Date:   Wed, 22 Nov 2023 11:03:58 +0000
From:   Sakari Ailus <sakari.ailus@iki.fi>
To:     Ricardo Ribalda <ribalda@chromium.org>
Cc:     Mauro Carvalho Chehab <mchehab@kernel.org>,
        Guenter Roeck <linux@roeck-us.net>,
        Tomasz Figa <tfiga@chromium.org>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        Alan Stern <stern@rowland.harvard.edu>,
        Hans Verkuil <hverkuil-cisco@xs4all.nl>,
        linux-media@vger.kernel.org, linux-kernel@vger.kernel.org,
        Sean Paul <seanpaul@chromium.org>,
        Sakari Ailus <sakari.ailus@linux.intel.com>
Subject: Re: [PATCH v3 2/3] media: uvcvideo: Do not halt the device after
 disconnect
Message-ID: <ZV3gHn8CuK_JJZbu@valkosipuli.retiisi.eu>
References: <20231121-guenter-mini-v3-0-d8a5eae2312b@chromium.org>
 <20231121-guenter-mini-v3-2-d8a5eae2312b@chromium.org>
 <ZV3XDtUKJPuGLhw9@valkosipuli.retiisi.eu>
 <CANiDSCuXXD_GWadSJo43zxscGAOPzxhODK=TKixn0OPn7z_tCw@mail.gmail.com>
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Hi Ricardo,

On Wed, Nov 22, 2023 at 11:32:16AM +0100, Ricardo Ribalda wrote:
> Hi Sakari
> 
> On Wed, 22 Nov 2023 at 11:25, Sakari Ailus <sakari.ailus@iki.fi> wrote:
> >
> > Hi Ricardo,
> >
> > Thank you for the patch.
> >
> > On Tue, Nov 21, 2023 at 07:53:49PM +0000, Ricardo Ribalda wrote:
> > > usb drivers should not call to any usb_() function after the
> > > .disconnect() callback has been triggered.
> > >
> > > If the camera is streaming, the uvc driver will call usb_set_interface or
> > > usb_clear_halt once the device is being released. Let's fix this issue.
> > >
> > > This is probably not the only driver affected with this kind of bug, but
> > > until there is a better way to do it in the core this is the way to
> > > solve this issue.
> > >
> > > When/if a different mechanism is implemented in the core to solve the
> > > lifetime of devices we will adopt it in uvc.
> > >
> > > Trace:
> > > [ 1065.389723] drivers/media/usb/uvc/uvc_driver.c:2248 uvc_disconnect enter
> > > [ 1065.390160] drivers/media/usb/uvc/uvc_driver.c:2264 uvc_disconnect exit
> > > [ 1065.433956] drivers/media/usb/uvc/uvc_v4l2.c:659 uvc_v4l2_release enter
> > > [ 1065.433973] drivers/media/usb/uvc/uvc_video.c:2274 uvc_video_stop_streaming enter
> > > [ 1065.434560] drivers/media/usb/uvc/uvc_video.c:2285 uvc_video_stop_streaming exit
> > > [ 1065.435154] drivers/media/usb/uvc/uvc_v4l2.c:680 uvc_v4l2_release exit
> > > [ 1065.435188] drivers/media/usb/uvc/uvc_driver.c:2248 uvc_disconnect enter
> > >
> > > Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
> > > ---
> > >  drivers/media/usb/uvc/uvc_driver.c |  2 ++
> > >  drivers/media/usb/uvc/uvc_video.c  | 45 ++++++++++++++++++++++++--------------
> > >  drivers/media/usb/uvc/uvcvideo.h   |  2 ++
> > >  3 files changed, 32 insertions(+), 17 deletions(-)
> > >
> > > diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
> > > index 08fcd2ffa727..413c32867617 100644
> > > --- a/drivers/media/usb/uvc/uvc_driver.c
> > > +++ b/drivers/media/usb/uvc/uvc_driver.c
> > > @@ -2257,6 +2257,8 @@ static void uvc_disconnect(struct usb_interface *intf)
> > >               return;
> > >
> > >       uvc_unregister_video(dev);
> > > +     /* Barrier needed to synchronize with uvc_video_stop_streaming(). */
> > > +     smp_store_release(&dev->disconnected, true);
> > >       kref_put(&dev->ref, uvc_delete);
> > >  }
> > >
> > > diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
> > > index 28dde08ec6c5..032b44e45b22 100644
> > > --- a/drivers/media/usb/uvc/uvc_video.c
> > > +++ b/drivers/media/usb/uvc/uvc_video.c
> > > @@ -2243,28 +2243,39 @@ int uvc_video_start_streaming(struct uvc_streaming *stream)
> > >       return ret;
> > >  }
> > >
> > > -void uvc_video_stop_streaming(struct uvc_streaming *stream)
> > > +static void uvc_video_halt(struct uvc_streaming *stream)
> > >  {
> > > -     uvc_video_stop_transfer(stream, 1);
> > > +     unsigned int epnum;
> > > +     unsigned int pipe;
> > > +     unsigned int dir;
> > >
> > >       if (stream->intf->num_altsetting > 1) {
> >
> > Doesn't this imply the device is using isochronous mode?
> 
> I haven't changed the behaviour for halt, it is just that git diff is
> being a bit too creative here:
> 
> Basically it is doing:
> 
> void video_halt() {
>    if (is_isoc()) {
>      usb_set_interface(stream->dev->udev, stream->intfnum, 0);
>      return;
>    }
>    usb_clear_halt();
> }
> 
> instead of the old:
> 
> void video_halt() {
>    if (is_isoc()) {
>      usb_set_interface(stream->dev->udev, stream->intfnum, 0);
>    }  else {
>       usb_clear_halt();
>    }
> }
> 
> Thanks!

Oops. I missed the removal of the else branch altogether while reading the
patch.

Shouldn't you also ensure the disconnect callback won't return until the
streaming has been stopped here?

> >
> > >               usb_set_interface(stream->dev->udev, stream->intfnum, 0);
> > > -     } else {
> > > -             /*
> > > -              * UVC doesn't specify how to inform a bulk-based device
> > > -              * when the video stream is stopped. Windows sends a
> > > -              * CLEAR_FEATURE(HALT) request to the video streaming
> > > -              * bulk endpoint, mimic the same behaviour.
> > > -              */
> > > -             unsigned int epnum = stream->header.bEndpointAddress
> > > -                                & USB_ENDPOINT_NUMBER_MASK;
> > > -             unsigned int dir = stream->header.bEndpointAddress
> > > -                              & USB_ENDPOINT_DIR_MASK;
> > > -             unsigned int pipe;
> > > -
> > > -             pipe = usb_sndbulkpipe(stream->dev->udev, epnum) | dir;
> > > -             usb_clear_halt(stream->dev->udev, pipe);
> > > +             return;
> > >       }
> > >
> > > +     /*
> > > +      * UVC doesn't specify how to inform a bulk-based device
> >
> > Then this comment doesn't look right. What about the code? This isn't
> > mentioned in the commit message either.
> >
> > > +      * when the video stream is stopped. Windows sends a
> > > +      * CLEAR_FEATURE(HALT) request to the video streaming
> > > +      * bulk endpoint, mimic the same behaviour.
> > > +      */
> > > +     epnum = stream->header.bEndpointAddress & USB_ENDPOINT_NUMBER_MASK;
> > > +     dir = stream->header.bEndpointAddress & USB_ENDPOINT_DIR_MASK;
> > > +     pipe = usb_sndbulkpipe(stream->dev->udev, epnum) | dir;
> > > +     usb_clear_halt(stream->dev->udev, pipe);
> > > +}
> > > +
> > > +void uvc_video_stop_streaming(struct uvc_streaming *stream)
> > > +{
> > > +     uvc_video_stop_transfer(stream, 1);
> > > +
> > > +     /*
> > > +      * Barrier needed to synchronize with uvc_disconnect().
> > > +      * We cannot call usb_* functions on a disconnected USB device.
> > > +      */
> > > +     if (!smp_load_acquire(&stream->dev->disconnected))
> > > +             uvc_video_halt(stream);
> > > +
> > >       uvc_video_clock_cleanup(stream);
> > >  }
> > > diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
> > > index 6fb0a78b1b00..4318ce8e31db 100644
> > > --- a/drivers/media/usb/uvc/uvcvideo.h
> > > +++ b/drivers/media/usb/uvc/uvcvideo.h
> > > @@ -559,6 +559,8 @@ struct uvc_device {
> > >       unsigned int users;
> > >       atomic_t nmappings;
> > >
> > > +     bool disconnected;
> > > +
> > >       /* Video control interface */
> > >  #ifdef CONFIG_MEDIA_CONTROLLER
> > >       struct media_device mdev;

-- 
Kind regards,

Sakari Ailus