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

[Daniel Vetter <daniel@ffwll.ch>]

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>

> -- 
> 2.8.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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