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Message-ID: <20240925192202.GD30399@pendragon.ideasonboard.com>
Date: Wed, 25 Sep 2024 22:22:02 +0300
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Ricardo Ribalda <ribalda@...omium.org>
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

On Wed, Sep 25, 2024 at 10:15:39PM +0300, Laurent Pinchart 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 ?

The uvc_status_start() function is also referenced in comments in this
file. If you keep the double undescore prefix they need to be renamed.

> >  {
> > +	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);
> 
> 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

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