Re: [PATCH] drm: Remove the deprecated drm_put_dev() function

[Sui Jingfeng <suijingfeng@xxxxxxxxxxx>]

Hi,

On 2023/6/26 15:48, Jani Nikula wrote:
> On Sun, 25 Jun 2023, Sui Jingfeng <suijingfeng@xxxxxxxxxxx> wrote:
> > As this function can be replaced with drm_dev_unregister() + drm_dev_put(),
> > it is already marked as deprecated, so remove it. No functional change.
> >
> > Signed-off-by: Sui Jingfeng <suijingfeng@xxxxxxxxxxx>
> > ---
> >   drivers/gpu/drm/drm_drv.c           | 28 ----------------------------
> >   drivers/gpu/drm/drm_pci.c           |  3 ++-
> >   drivers/gpu/drm/radeon/radeon_drv.c |  3 ++-
> >   include/drm/drm_drv.h               |  1 -
> >   4 files changed, 4 insertions(+), 31 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
> > index 12687dd9e1ac..5057307fe22a 100644
> > --- a/drivers/gpu/drm/drm_drv.c
> > +++ b/drivers/gpu/drm/drm_drv.c
> > @@ -406,34 +406,6 @@ void drm_minor_release(struct drm_minor *minor)
> >    * possibly leaving the hardware enabled.
> >    */
> >   
> > -/**
> > - * drm_put_dev - Unregister and release a DRM device
> > - * @dev: DRM device
> > - *
> > - * Called at module unload time or when a PCI device is unplugged.
> > - *
> > - * Cleans up all DRM device, calling drm_lastclose().
> > - *
> > - * Note: Use of this function is deprecated. It will eventually go away
> > - * completely.  Please use drm_dev_unregister() and drm_dev_put() explicitly
> > - * instead to make sure that the device isn't userspace accessible any more
> > - * while teardown is in progress, ensuring that userspace can't access an
> > - * inconsistent state.
> The last sentence is the crucial one. While the patch has no functional
> changes,

But my patch help to save a useless check(if (!dev))

on where we found the check is not necessary.

```

-	if (!dev) {
-		DRM_ERROR("cleanup called no dev\n");
-		return;
-	}

```


> I believe the goal never was to just mechanically replace one
> call with the two.

The DRM core lose nothing, just a function wrapper.

Instead, this is probably a good chance to migrate the burden to the 
driver side.

I think the device driver(drm/radeon, for example) have better understanding

about how to ensure that userspace can't access an inconsistent state 
than the DRM core.

> BR,
> Jani.
>
>
> > - */
> > -void drm_put_dev(struct drm_device *dev)
> > -{
> > -	DRM_DEBUG("\n");
> > -
> > -	if (!dev) {
> > -		DRM_ERROR("cleanup called no dev\n");
> > -		return;
> > -	}
> > -
> > -	drm_dev_unregister(dev);
> > -	drm_dev_put(dev);
> > -}
> > -EXPORT_SYMBOL(drm_put_dev);
> > -
> >   /**
> >    * drm_dev_enter - Enter device critical section
> >    * @dev: DRM device
> > diff --git a/drivers/gpu/drm/drm_pci.c b/drivers/gpu/drm/drm_pci.c
> > index 39d35fc3a43b..b3a68a92eaa6 100644
> > --- a/drivers/gpu/drm/drm_pci.c
> > +++ b/drivers/gpu/drm/drm_pci.c
> > @@ -257,7 +257,8 @@ void drm_legacy_pci_exit(const struct drm_driver *driver,
> >   					 legacy_dev_list) {
> >   			if (dev->driver == driver) {
> >   				list_del(&dev->legacy_dev_list);
> > -				drm_put_dev(dev);
> > +				drm_dev_unregister(dev);
> > +				drm_dev_put(dev);
> >   			}
> >   		}
> >   		mutex_unlock(&legacy_dev_list_lock);
> > diff --git a/drivers/gpu/drm/radeon/radeon_drv.c b/drivers/gpu/drm/radeon/radeon_drv.c
> > index e4374814f0ef..a4955ae10659 100644
> > --- a/drivers/gpu/drm/radeon/radeon_drv.c
> > +++ b/drivers/gpu/drm/radeon/radeon_drv.c
> > @@ -357,7 +357,8 @@ radeon_pci_remove(struct pci_dev *pdev)
> >   {
> >   	struct drm_device *dev = pci_get_drvdata(pdev);
> >   
> > -	drm_put_dev(dev);
> > +	drm_dev_unregister(dev);
> > +	drm_dev_put(dev);
> >   }
> >   
> >   static void
> > diff --git a/include/drm/drm_drv.h b/include/drm/drm_drv.h
> > index 89e2706cac56..289c97b12e82 100644
> > --- a/include/drm/drm_drv.h
> > +++ b/include/drm/drm_drv.h
> > @@ -511,7 +511,6 @@ void drm_dev_unregister(struct drm_device *dev);
> >   
> >   void drm_dev_get(struct drm_device *dev);
> >   void drm_dev_put(struct drm_device *dev);
> > -void drm_put_dev(struct drm_device *dev);
> >   bool drm_dev_enter(struct drm_device *dev, int *idx);
> >   void drm_dev_exit(int idx);
> >   void drm_dev_unplug(struct drm_device *dev);

--
Jingfeng