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

[Sui Jingfeng <suijingfeng@xxxxxxxxxxx>]

Hi,

On 2023/6/26 15:56, Thomas Zimmermann wrote:
> Hi
>
> Am 25.06.23 um 07:09 schrieb Sui Jingfeng:
> > 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.
> > - */
> > -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);
>
> Did you verify that dev cannot be NULL here? There was a check in 
> drm_put_dev() for !dev.

I have verified :


1)

If there is no radeon card(say R5-340) mounted in the system,  I 
modprobe the radeon.ko manually.

then both the radeon_pci_probe() and the radeon_pci_remove() function 
won't get called.

There is no chance that the driver_probe_device() function getting called.


|- driver_register()

|-- bus_add_driver()

|--- driver_attach()

|---- bus_for_each_dev(drv->bus, NULL, drv, __driver_attach)

|----- __driver_attach()

|------ __device_attach_driver()

// There is no chance that the driver_probe_device() function get called.

|------- driver_probe_device(drv, dev)

```


2)  normal case:


If there are radeon cards mounted in the system,

then as long as the pci_set_drvdata(pdev, dev) get called,

the 'driver_data' member of struct device will hold the pointer to the 
'struct drm_device';

So, it will be fine as long as the radeon.ko get loaded normally.


I'm sure it will works as expected on normal case, with 100% confident.


3) Abnormal case

If there is a error happen before the 'pci_set_drvdata(pdev, dev)' 
function get called.

It is also don't need to worry, if the ->probe() failed, then the 
->remove will be get called.


I have verified that

if the ->probe() failed, then the ->remove will be get called.

I'm doing the test by add a line before the drm_dev_alloc()

function in the body of radeon_pci_probe() function.

See below:

```

    return -ENODEV;

    dev = drm_dev_alloc(&kms_driver, &pdev->dev);
    if (IS_ERR(dev))
        return PTR_ERR(dev);

    ret = pci_enable_device(pdev);
    if (ret)
        goto err_free;
```


So, there is no problem, as far as I can see.


> Best regards
> Thomas
>
> > +    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