Re: [PATCH 02/44] drm: Add devm_drm_dev_alloc macro

[Sam Ravnborg <sam@ravnborg.org>]

Hi Daniel.

Finally managed to dive into this..

Maybe I need more coffee, it is still morning here.
But alas this patch triggered a few comments.

	Sam

On Fri, Apr 03, 2020 at 03:57:46PM +0200, Daniel Vetter wrote:
> The kerneldoc is only added for this new function. Existing kerneldoc
> and examples will be udated at the very end, since once all drivers
> are converted over to devm_drm_dev_alloc we can unexport a lot of
> interim functions and make the documentation for driver authors a lot
> cleaner and less confusing. There will be only one true way to
> initialize a drm_device at the end of this, which is going to be
> devm_drm_dev_alloc.

This changelog entry does a poor job describing what the purpose of this
change is.
Try to read it outside context.


> 
> Cc: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
> Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> ---
>  drivers/gpu/drm/drm_drv.c | 23 +++++++++++++++++++++++
>  include/drm/drm_drv.h     | 33 +++++++++++++++++++++++++++++++++
>  2 files changed, 56 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
> index 1bb4f636b83c..9e60b784b3ac 100644
> --- a/drivers/gpu/drm/drm_drv.c
> +++ b/drivers/gpu/drm/drm_drv.c
> @@ -739,6 +739,29 @@ int devm_drm_dev_init(struct device *parent,
>  }
>  EXPORT_SYMBOL(devm_drm_dev_init);
>  
> +void* __devm_drm_dev_alloc(struct device *parent, struct drm_driver *driver,
> +			   size_t size, size_t offset)
> +{
> +	void *container;
> +	struct drm_device *drm;
> +	int ret;
> +
> +	container = kzalloc(size, GFP_KERNEL);
> +	if (!container)
> +		return ERR_PTR(-ENOMEM);
> +
> +	drm = container + offset;
> +	ret = devm_drm_dev_init(parent, drm, driver);
> +	if (ret) {
> +		kfree(container);
> +		return ERR_PTR(ret);
> +	}
> +	drmm_add_final_kfree(drm, container);
> +
> +	return container;
> +}
> +EXPORT_SYMBOL(__devm_drm_dev_alloc);
> +
>  /**
>   * drm_dev_alloc - Allocate new DRM device
>   * @driver: DRM driver to allocate device for
> diff --git a/include/drm/drm_drv.h b/include/drm/drm_drv.h
> index e7c6ea261ed1..26776be5a21e 100644
> --- a/include/drm/drm_drv.h
> +++ b/include/drm/drm_drv.h
> @@ -626,6 +626,39 @@ int devm_drm_dev_init(struct device *parent,
>  		      struct drm_device *dev,
>  		      struct drm_driver *driver);
>  
> +void* __devm_drm_dev_alloc(struct device *parent, struct drm_driver *driver,
> +			   size_t size, size_t offset);
> +
> +/**
> + * devm_drm_dev_alloc - Resource managed allocation of a &drm_device instance
> + * @parent: Parent device object
> + * @driver: DRM driver
> + * @type: the type of the struct which contains struct &drm_device
> + * @member: the name of the &drm_device within @type.
I am confused about the naming here.
devm_ implies we allocate something with a lifetime equal that of a
driver. So when the driver are gone what we allocate is also gone.
Like everythign else devm_ prefixed.

But the lifetime of a drm_device is until the last userspace reference
is gone (final drm_dev_put() is called).

> + *
> + * This allocates 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
s/This/Calling drm_dev_register()/ will make this sentence a bit more
explicit.

> + * initialization sequence to make sure userspace can't access an inconsistent
> + * state.
> + *
> + * The initial ref-count of the object is 1. Use drm_dev_get() and
> + * drm_dev_put() to take and drop further ref-counts.
> + *
> + * It is recommended that drivers embed &struct drm_device into their own device
> + * structure.
> + *
> + * Note that this manages the lifetime of the resulting &drm_device
> + * automatically using devres.
Hmm, no this is managed by drmres???


> + * The DRM device initialized with this function is
> + * automatically put on driver detach using drm_dev_put().
> + *
> + * RETURNS:
> + * Pointer to new DRM device, or ERR_PTR on failure.
> + */
> +#define devm_drm_dev_alloc(parent, driver, type, member) \
> +	((type *) __devm_drm_dev_alloc(parent, driver, sizeof(type), \
> +				       offsetof(type, member)))
> +
>  struct drm_device *drm_dev_alloc(struct drm_driver *driver,
>  				 struct device *parent);
>  int drm_dev_register(struct drm_device *dev, unsigned long flags);
> -- 
> 2.25.1
> 
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