Re: [PATCH v2 01/21] drm: Export drm_dev_init() for subclassing

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Jun 01, 2016 at 12:01:44PM +0200, Daniel Vetter wrote:
> On Mon, May 30, 2016 at 09:38:19AM +0100, Chris Wilson wrote:
> > In order to allow drivers to pack their privates and drm_device into one
> > struct (e.g. for subclassing), export the initialisation routines for
> > struct drm_device.
> > 
> > v2: Missed return ret. That error path had only one job to do!
> > 
> > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> > Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> > Cc: dri-devel@lists.freedesktop.org
> > ---
> >  drivers/gpu/drm/drm_drv.c | 63 ++++++++++++++++++++++++++++++++++++-----------
> >  include/drm/drmP.h        |  3 +++
> >  2 files changed, 52 insertions(+), 14 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
> > index bff89226a344..f0553ccd4f71 100644
> > --- a/drivers/gpu/drm/drm_drv.c
> > +++ b/drivers/gpu/drm/drm_drv.c
> > @@ -549,11 +549,12 @@ static void drm_fs_inode_free(struct inode *inode)
> >  }
> >  
> >  /**
> > - * drm_dev_alloc - Allocate new DRM device
> > - * @driver: DRM driver to allocate device for
> > + * drm_dev_init - Initialise new DRM device
> > + * @dev: DRM device
> > + * @driver: DRM driver
> >   * @parent: Parent device object
> >   *
> > - * Allocate and initialize a new DRM device. No device registration is done.
> > + * Initialize a new DRM device. No device registration is done.
> >   * Call drm_dev_register() to advertice the device to user space and register it
> >   * with other core subsystems. This should be done last in the device
> >   * initialization sequence to make sure userspace can't access an inconsistent
> > @@ -565,18 +566,14 @@ static void drm_fs_inode_free(struct inode *inode)
> >   * Note that for purely virtual devices @parent can be NULL.
> 
> Maybe add "Drivers which don't want to allocate their own device structure
> embedding &drm_device can instead just call drm_dev_alloc()."
> >   *
> >   * RETURNS:
> > - * Pointer to new DRM device, or NULL if out of memory.
> > + * 0 on success, or error code on failure.
> >   */
> > -struct drm_device *drm_dev_alloc(struct drm_driver *driver,
> > -				 struct device *parent)
> > +int drm_dev_init(struct drm_device *dev,
> > +		 struct drm_driver *driver,
> > +		 struct device *parent)
> >  {
> > -	struct drm_device *dev;
> >  	int ret;
> >  
> > -	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
> > -	if (!dev)
> > -		return NULL;
> > -
> >  	kref_init(&dev->ref);
> >  	dev->dev = parent;
> >  	dev->driver = driver;
> > @@ -638,7 +635,7 @@ struct drm_device *drm_dev_alloc(struct drm_driver *driver,
> >  			goto err_setunique;
> >  	}
> >  
> > -	return dev;
> > +	return 0;
> >  
> >  err_setunique:
> >  	if (drm_core_check_feature(dev, DRIVER_GEM))
> > @@ -653,8 +650,46 @@ err_minors:
> >  	drm_fs_inode_free(dev->anon_inode);
> >  err_free:
> >  	mutex_destroy(&dev->master_mutex);
> > -	kfree(dev);
> > -	return NULL;
> > +	return ret;
> 
> for "goto err_minors" you need to set ret first, otherwise we'll fail and
> return 0. Wasn't a problem because of the unconditional return NULL here.
> 
> > +}
> > +EXPORT_SYMBOL(drm_dev_init);
> > +
> > +/**
> > + * drm_dev_alloc - Allocate new DRM device
> > + * @driver: DRM driver to allocate device for
> > + * @parent: Parent device object
> > + *
> > + * Allocate and initialize a new DRM device. No device registration is done.
> > + * Call drm_dev_register() to advertice the device to user space and register it
> > + * with other core subsystems. This should be done last in the device
> > + * initialization sequence to make sure userspace can't access an inconsistent
> > + * state.
> > + *
> > + * The initial ref-count of the object is 1. Use drm_dev_ref() and
> > + * drm_dev_unref() to take and drop further ref-counts.
> > + *
> > + * Note that for purely virtual devices @parent can be NULL.
> 
> Maybe we can also add "Drivers which want to subclass/embed struct
> &drm_device should instead look at drm_dev_init()."
> 
> > + *
> > + * RETURNS:
> > + * Pointer to new DRM device, or NULL if out of memory.
> > + */
> > +struct drm_device *drm_dev_alloc(struct drm_driver *driver,
> > +				 struct device *parent)
> > +{
> > +	struct drm_device *dev;
> > +	int ret;
> > +
> > +	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
> > +	if (!dev)
> > +		return NULL;
> > +
> > +	ret = drm_dev_init(dev, driver, parent);
> > +	if (ret) {
> > +		kfree(dev);
> > +		return NULL;
> > +	}
> > +
> > +	return dev;
> >  }
> >  EXPORT_SYMBOL(drm_dev_alloc);
> >  
> > diff --git a/include/drm/drmP.h b/include/drm/drmP.h
> > index c5d29505f937..12dc5f9cad89 100644
> > --- a/include/drm/drmP.h
> > +++ b/include/drm/drmP.h
> > @@ -1075,6 +1075,9 @@ extern void drm_sysfs_hotplug_event(struct drm_device *dev);
> >  
> >  struct drm_device *drm_dev_alloc(struct drm_driver *driver,
> >  				 struct device *parent);
> > +int drm_dev_init(struct drm_device *dev,
> > +		 struct drm_driver *driver,
> > +		 struct device *parent);
> >  void drm_dev_ref(struct drm_device *dev);
> >  void drm_dev_unref(struct drm_device *dev);
> >  int drm_dev_register(struct drm_device *dev, unsigned long flags);
> 
> With the one bug in the error handling fixed, and the kerneldoc augmented:
> 
> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

r-b retracted, this is a bit incomplete since it doesn't handle
drm_dev_release. I think we also should add an optional ->device_free
callback and use that in drm_dev_release instead of kfree().

That would finally make the drm_device refcounting also somewhat useful,
since right now you have to release driver-private stuff before the device
is actually gone, which is buggy. Or just leak, which is also buggy ;-)
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/dri-devel