Re: [PATCH v2 11/29] media: mc: Split initialising and adding media devnode

[Sakari Ailus <sakari.ailus@linux.intel.com>]

Hi Laurent,

Thanks for the review.

On Wed, Feb 07, 2024 at 12:46:13PM +0200, Laurent Pinchart wrote:
> Hi Sakari,
> 
> Thank you for the patch.
> 
> On Wed, Dec 20, 2023 at 12:36:55PM +0200, Sakari Ailus wrote:
> > As registering a device node of an entity belonging to a media device
> 
> Did you mean s/As registering/Registering/ ?

That works better in the current context. I'll use that.

> 
> > will require a reference to the struct device. Taking that reference is
> > only possible once the device has been initialised, which took place only
> 
> s/took/takes/
> 
> > when it was registered. Split this in two, and initialise the device when
> 
> s/was/is/

This describes the behaviour before the patch. I think it makes sense to
use imperfect here.

> 
> > the media device is allocated.
> > 
> > Don't distribute the effects of these changes yet. Add media_device_get()
> > and media_device_put() first.
> 
> Don't propagate the effects of these changes to drivers yet, we want to
> expose media_device refcounting with media_device_get() and
> media_device_put() functions first.
> 
> 
> I'm not sure that's exactly what you meant though.

Yes, that's roughly what I meant, I can use the above text.

> 
> > Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> > Acked-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
> 
> Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

Thanks!

> 
> > ---
> >  drivers/media/mc/mc-device.c  | 18 +++++++++++++-----
> >  drivers/media/mc/mc-devnode.c | 17 ++++++++++-------
> >  include/media/media-devnode.h | 19 ++++++++++++++-----
> >  3 files changed, 37 insertions(+), 17 deletions(-)
> > 
> > diff --git a/drivers/media/mc/mc-device.c b/drivers/media/mc/mc-device.c
> > index c0ea08a8fc31..ebf037cd5f4a 100644
> > --- a/drivers/media/mc/mc-device.c
> > +++ b/drivers/media/mc/mc-device.c
> > @@ -717,19 +717,26 @@ int __must_check __media_device_register(struct media_device *mdev,
> >  	/* Set version 0 to indicate user-space that the graph is static */
> >  	mdev->topology_version = 0;
> >  
> > +	media_devnode_init(&mdev->devnode);
> > +
> >  	ret = media_devnode_register(&mdev->devnode, owner);
> >  	if (ret < 0)
> > -		return ret;
> > +		goto out_put;
> >  
> >  	ret = device_create_file(&mdev->devnode.dev, &dev_attr_model);
> > -	if (ret < 0) {
> > -		media_devnode_unregister(&mdev->devnode);
> > -		return ret;
> > -	}
> > +	if (ret < 0)
> > +		goto out_unregister;
> >  
> >  	dev_dbg(mdev->dev, "Media device registered\n");
> >  
> >  	return 0;
> > +
> > +out_unregister:
> 
> I would name the labels err_unregister and err_put.

Sounds good.

> 
> > +	media_devnode_unregister(&mdev->devnode);
> > +out_put:
> > +	put_device(&mdev->devnode.dev);
> > +
> > +	return ret;
> >  }
> >  EXPORT_SYMBOL_GPL(__media_device_register);
> >  
> > @@ -803,6 +810,7 @@ void media_device_unregister(struct media_device *mdev)
> >  	device_remove_file(&mdev->devnode.dev, &dev_attr_model);
> >  	dev_dbg(mdev->dev, "Media device unregistering\n");
> >  	media_devnode_unregister(&mdev->devnode);
> > +	put_device(&mdev->devnode.dev);
> >  }
> >  EXPORT_SYMBOL_GPL(media_device_unregister);
> >  
> > diff --git a/drivers/media/mc/mc-devnode.c b/drivers/media/mc/mc-devnode.c
> > index 8bc7450ac144..7b17419050fb 100644
> > --- a/drivers/media/mc/mc-devnode.c
> > +++ b/drivers/media/mc/mc-devnode.c
> > @@ -204,6 +204,11 @@ static const struct file_operations media_devnode_fops = {
> >  	.llseek = no_llseek,
> >  };
> >  
> > +void media_devnode_init(struct media_devnode *devnode)
> > +{
> > +	device_initialize(&devnode->dev);
> > +}
> > +
> >  int __must_check media_devnode_register(struct media_devnode *devnode,
> >  					struct module *owner)
> >  {
> > @@ -235,7 +240,6 @@ int __must_check media_devnode_register(struct media_devnode *devnode,
> >  	if (devnode->parent)
> >  		devnode->dev.parent = devnode->parent;
> >  	dev_set_name(&devnode->dev, "media%d", devnode->minor);
> > -	device_initialize(&devnode->dev);
> >  
> >  	/* Part 3: Add the media and character devices */
> >  	ret = cdev_device_add(&devnode->cdev, &devnode->dev);
> > @@ -267,14 +271,13 @@ void media_devnode_unregister(struct media_devnode *devnode)
> >  	clear_bit(MEDIA_FLAG_REGISTERED, &devnode->flags);
> >  	mutex_unlock(&media_devnode_lock);
> >  
> > -	cdev_del(&devnode->cdev);
> > -	device_unregister(&devnode->dev);
> > +	cdev_device_del(&devnode->cdev, &devnode->dev);
> >  }
> >  
> >  /*
> >   *	Initialise media for linux
> >   */
> > -static int __init media_devnode_init(void)
> > +static int __init media_devnode_module_init(void)
> >  {
> >  	int ret;
> >  
> > @@ -296,14 +299,14 @@ static int __init media_devnode_init(void)
> >  	return 0;
> >  }
> >  
> > -static void __exit media_devnode_exit(void)
> > +static void __exit media_devnode_module_exit(void)
> >  {
> >  	bus_unregister(&media_bus_type);
> >  	unregister_chrdev_region(media_dev_t, MEDIA_NUM_DEVICES);
> >  }
> >  
> > -subsys_initcall(media_devnode_init);
> > -module_exit(media_devnode_exit)
> > +subsys_initcall(media_devnode_module_init);
> > +module_exit(media_devnode_module_exit)
> >  
> >  MODULE_AUTHOR("Laurent Pinchart <laurent.pinchart@ideasonboard.com>");
> >  MODULE_DESCRIPTION("Device node registration for media drivers");
> > diff --git a/include/media/media-devnode.h b/include/media/media-devnode.h
> > index 1117d1dfd6bf..6d46c658be21 100644
> > --- a/include/media/media-devnode.h
> > +++ b/include/media/media-devnode.h
> > @@ -90,6 +90,17 @@ struct media_devnode {
> >  /* dev to media_devnode */
> >  #define to_media_devnode(cd) container_of(cd, struct media_devnode, dev)
> >  
> > +/**
> > + * media_devnode_init - initialise a media devnode
> > + *
> > + * @devnode: struct media_devnode we want to initialise
> > + *
> > + * Initialise a media devnode. Note that after initialising the media
> > + * devnode is refcounted. Releasing references to it may be done using
> > + * put_device().
> > + */
> > +void media_devnode_init(struct media_devnode *devnode);
> > +
> >  /**
> >   * media_devnode_register - register a media device node
> >   *
> > @@ -100,11 +111,9 @@ struct media_devnode {
> >   * with the kernel. An error is returned if no free minor number can be found,
> >   * or if the registration of the device node fails.
> >   *
> > - * Zero is returned on success.
> > - *
> > - * Note that if the media_devnode_register call fails, the release() callback of
> > - * the media_devnode structure is *not* called, so the caller is responsible for
> > - * freeing any data.
> > + * Zero is returned on success. Note that in case
> > + * media_devnode_register() fails, the caller is responsible for
> > + * releasing the reference to the device using put_device().
> >   */
> >  int __must_check media_devnode_register(struct media_devnode *devnode,
> >  					struct module *owner);
> 

-- 
Regards,

Sakari Ailus