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Message-ID: <CANiDSCvOMV6J1cTnGdmnsUCzj=N9vXNFVSm6LQC8LfOCNPu9=Q@mail.gmail.com>
Date: Thu, 26 Sep 2024 07:33:25 +0200
From: Ricardo Ribalda <ribalda@...omium.org>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc: Mauro Carvalho Chehab <mchehab@...nel.org>, Guenter Roeck <linux@...ck-us.net>,
Tomasz Figa <tfiga@...omium.org>, Alan Stern <stern@...land.harvard.edu>,
Hans Verkuil <hverkuil-cisco@...all.nl>, linux-media@...r.kernel.org,
linux-kernel@...r.kernel.org, Sean Paul <seanpaul@...omium.org>,
Sakari Ailus <sakari.ailus@...ux.intel.com>,
Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: Re: [PATCH v6 2/4] media: uvcvideo: Refactor the status irq API
Hi Laurent
On Wed, 25 Sept 2024 at 21:15, Laurent Pinchart
<laurent.pinchart@...asonboard.com> wrote:
>
> Hi Ricardo,
>
> Thank you for the patch.
>
> On Fri, Jun 14, 2024 at 12:41:28PM +0000, Ricardo Ribalda wrote:
> > There are two different use-cases of uvc_status():
>
> I'd add a blank line here, and remove the leading tabs from the next two
> lines.
>
> > - adding/removing a user when the camera is open/closed
> > - stopping/starting when the camera is suspended/resumed
> >
> > Make the API reflect these two use-cases and move all the refcounting
> > and locking logic to the uvc_status.c file.
>
> If my understanding is correct, this doesn't introduce any functional
> change, and is not a dependency of further patches in the series. I
> don't have a strong opinion on the refactoring itself, so I'm fine with
> it, but I'd like a mention in the commit message that no functional
> change is introduced.
>
> > Reviewed-by: Sergey Senozhatsky <senozhatsky@...omium.org>
> > Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> > ---
> > drivers/media/usb/uvc/uvc_driver.c | 13 ++-------
> > drivers/media/usb/uvc/uvc_status.c | 55 ++++++++++++++++++++++++++++++++++++--
> > drivers/media/usb/uvc/uvc_v4l2.c | 22 +++++----------
> > drivers/media/usb/uvc/uvcvideo.h | 10 ++++---
> > 4 files changed, 67 insertions(+), 33 deletions(-)
> >
> > diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
> > index 55132688e363..c8c0352af1e5 100644
> > --- a/drivers/media/usb/uvc/uvc_driver.c
> > +++ b/drivers/media/usb/uvc/uvc_driver.c
> > @@ -2135,7 +2135,6 @@ static int uvc_probe(struct usb_interface *intf,
> > INIT_LIST_HEAD(&dev->streams);
> > kref_init(&dev->ref);
> > atomic_set(&dev->nmappings, 0);
> > - mutex_init(&dev->lock);
> >
> > dev->udev = usb_get_dev(udev);
> > dev->intf = usb_get_intf(intf);
> > @@ -2301,10 +2300,7 @@ static int uvc_suspend(struct usb_interface *intf, pm_message_t message)
> > /* Controls are cached on the fly so they don't need to be saved. */
> > if (intf->cur_altsetting->desc.bInterfaceSubClass ==
> > UVC_SC_VIDEOCONTROL) {
> > - mutex_lock(&dev->lock);
> > - if (dev->users)
> > - uvc_status_stop(dev);
> > - mutex_unlock(&dev->lock);
> > + uvc_status_suspend(dev);
> > return 0;
> > }
> >
> > @@ -2335,12 +2331,7 @@ static int __uvc_resume(struct usb_interface *intf, int reset)
> > return ret;
> > }
> >
> > - mutex_lock(&dev->lock);
> > - if (dev->users)
> > - ret = uvc_status_start(dev, GFP_NOIO);
> > - mutex_unlock(&dev->lock);
> > -
> > - return ret;
> > + return uvc_status_resume(dev);
> > }
> >
> > list_for_each_entry(stream, &dev->streams, list) {
> > diff --git a/drivers/media/usb/uvc/uvc_status.c b/drivers/media/usb/uvc/uvc_status.c
> > index a78a88c710e2..375a95dd3011 100644
> > --- a/drivers/media/usb/uvc/uvc_status.c
> > +++ b/drivers/media/usb/uvc/uvc_status.c
> > @@ -257,6 +257,8 @@ int uvc_status_init(struct uvc_device *dev)
> > unsigned int pipe;
> > int interval;
> >
> > + mutex_init(&dev->status_lock);
> > +
> > if (ep == NULL)
> > return 0;
> >
> > @@ -302,18 +304,22 @@ void uvc_status_cleanup(struct uvc_device *dev)
> > kfree(dev->status);
> > }
> >
> > -int uvc_status_start(struct uvc_device *dev, gfp_t flags)
> > +static int __uvc_status_start(struct uvc_device *dev, gfp_t flags)
>
> Do we need a double underscore prefix here and for the stop() function ?
>
> > {
> > + lockdep_assert_held(&dev->status_lock);
> > +
> > if (dev->int_urb == NULL)
> > return 0;
> >
> > return usb_submit_urb(dev->int_urb, flags);
> > }
> >
> > -void uvc_status_stop(struct uvc_device *dev)
> > +static void __uvc_status_stop(struct uvc_device *dev)
> > {
> > struct uvc_ctrl_work *w = &dev->async_ctrl;
> >
> > + lockdep_assert_held(&dev->status_lock);
> > +
> > /*
> > * Prevent the asynchronous control handler from requeing the URB. The
> > * barrier is needed so the flush_status change is visible to other
> > @@ -350,3 +356,48 @@ void uvc_status_stop(struct uvc_device *dev)
> > */
> > smp_store_release(&dev->flush_status, false);
> > }
> > +
> > +int uvc_status_resume(struct uvc_device *dev)
> > +{
> > + int ret = 0;
> > +
> > + mutex_lock(&dev->status_lock);
> > + if (dev->status_users)
> > + ret = __uvc_status_start(dev, GFP_NOIO);
> > + mutex_unlock(&dev->status_lock);
> > +
> > + return ret;
>
> Now that we have scoped guards, this can be written as
>
> guard(mutex)(&dev->status_lock);
>
> if (!dev->status_users)
> return 0;
>
> return __uvc_status_start(dev, GFP_NOIO);
>
> > +}
> > +
> > +void uvc_status_suspend(struct uvc_device *dev)
> > +{
> > + mutex_lock(&dev->status_lock);
> > + if (dev->status_users)
> > + __uvc_status_stop(dev);
> > + mutex_unlock(&dev->status_lock);
>
> guard(mutex)(&dev->status_lock);
>
> if (dev->status_users)
> __uvc_status_stop(dev);
>
> Same below.
>
> > +}
> > +
> > +int uvc_status_get(struct uvc_device *dev)
> > +{
> > + int ret = 0;
> > +
> > + mutex_lock(&dev->status_lock);
> > + if (!dev->status_users)
> > + ret = __uvc_status_start(dev, GFP_KERNEL);
> > + if (!ret)
> > + dev->status_users++;
> > + mutex_unlock(&dev->status_lock);
> > +
> > + return ret;
> > +}
> > +
> > +void uvc_status_put(struct uvc_device *dev)
> > +{
> > + mutex_lock(&dev->status_lock);
> > + if (dev->status_users == 1)
> > + __uvc_status_stop(dev);
> > + WARN_ON(!dev->status_users);
>
> Is this needed, or could we keep the original code ?
>
> if (--dev->status_users == 0)
> __uvc_status_stop(dev);
I'd prefer to keep the code. When I was playing with the granular PM
it was very nice to display a WARN and make sure that status_users was
never underflowed.
>
> All those comments are quite minor, the next version will have my R-b.
>
> > + if (dev->status_users)
> > + dev->status_users--;
> > + mutex_unlock(&dev->status_lock);
> > +}
> > diff --git a/drivers/media/usb/uvc/uvc_v4l2.c b/drivers/media/usb/uvc/uvc_v4l2.c
> > index f4988f03640a..97c5407f6603 100644
> > --- a/drivers/media/usb/uvc/uvc_v4l2.c
> > +++ b/drivers/media/usb/uvc/uvc_v4l2.c
> > @@ -628,20 +628,13 @@ static int uvc_v4l2_open(struct file *file)
> > return -ENOMEM;
> > }
> >
> > - mutex_lock(&stream->dev->lock);
> > - if (stream->dev->users == 0) {
> > - ret = uvc_status_start(stream->dev, GFP_KERNEL);
> > - if (ret < 0) {
> > - mutex_unlock(&stream->dev->lock);
> > - usb_autopm_put_interface(stream->dev->intf);
> > - kfree(handle);
> > - return ret;
> > - }
> > + ret = uvc_status_get(stream->dev);
> > + if (ret) {
> > + usb_autopm_put_interface(stream->dev->intf);
> > + kfree(handle);
> > + return ret;
> > }
> >
> > - stream->dev->users++;
> > - mutex_unlock(&stream->dev->lock);
> > -
> > v4l2_fh_init(&handle->vfh, &stream->vdev);
> > v4l2_fh_add(&handle->vfh);
> > handle->chain = stream->chain;
> > @@ -670,10 +663,7 @@ static int uvc_v4l2_release(struct file *file)
> > kfree(handle);
> > file->private_data = NULL;
> >
> > - mutex_lock(&stream->dev->lock);
> > - if (--stream->dev->users == 0)
> > - uvc_status_stop(stream->dev);
> > - mutex_unlock(&stream->dev->lock);
> > + uvc_status_put(stream->dev);
> >
> > usb_autopm_put_interface(stream->dev->intf);
> > return 0;
> > diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
> > index 6fb0a78b1b00..00b600eb058c 100644
> > --- a/drivers/media/usb/uvc/uvcvideo.h
> > +++ b/drivers/media/usb/uvc/uvcvideo.h
> > @@ -555,8 +555,6 @@ struct uvc_device {
> >
> > const struct uvc_device_info *info;
> >
> > - struct mutex lock; /* Protects users */
> > - unsigned int users;
> > atomic_t nmappings;
> >
> > /* Video control interface */
> > @@ -578,6 +576,8 @@ struct uvc_device {
> > struct usb_host_endpoint *int_ep;
> > struct urb *int_urb;
> > struct uvc_status *status;
> > + struct mutex status_lock; /* Protects status_users */
> > + unsigned int status_users;
> > bool flush_status;
> >
> > struct input_dev *input;
> > @@ -744,8 +744,10 @@ int uvc_register_video_device(struct uvc_device *dev,
> > int uvc_status_init(struct uvc_device *dev);
> > void uvc_status_unregister(struct uvc_device *dev);
> > void uvc_status_cleanup(struct uvc_device *dev);
> > -int uvc_status_start(struct uvc_device *dev, gfp_t flags);
> > -void uvc_status_stop(struct uvc_device *dev);
> > +int uvc_status_resume(struct uvc_device *dev);
> > +void uvc_status_suspend(struct uvc_device *dev);
> > +int uvc_status_get(struct uvc_device *dev);
> > +void uvc_status_put(struct uvc_device *dev);
> >
> > /* Controls */
> > extern const struct uvc_control_mapping uvc_ctrl_power_line_mapping_limited;
>
> --
> Regards,
>
> Laurent Pinchart
--
Ricardo Ribalda
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