[RFC 1/7] drm/gem: Add drm_gem_dumb_map_offset()

[Noralf Trønnes]

Den 12.07.2017 15.45, skrev Noralf Trønnes:
> Add a common drm_driver.dumb_map_offset function for GEM backed drivers.
>
> Signed-off-by: Noralf Trønnes <noralf at tronnes.org>
> ---
>   drivers/gpu/drm/drm_gem.c | 35 +++++++++++++++++++++++++++++++++++
>   include/drm/drm_gem.h     |  2 ++
>   2 files changed, 37 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
> index 8dc1106..44ecbaa 100644
> --- a/drivers/gpu/drm/drm_gem.c
> +++ b/drivers/gpu/drm/drm_gem.c
> @@ -311,6 +311,41 @@ drm_gem_handle_delete(struct drm_file *filp, u32 handle)
>   EXPORT_SYMBOL(drm_gem_handle_delete);
>   
>   /**
> + * drm_gem_dumb_map_offset - return the fake mmap offset for a gem object
> + * @file: drm file-private structure containing the gem object
> + * @dev: corresponding drm_device
> + * @handle: gem object handle
> + * @offset: return location for the fake mmap offset
> + *
> + * This implements the &drm_driver.dumb_map_offset kms driver callback for
> + * drivers which use gem to manage their backing storage.
> + *
> + * Returns:
> + * 0 on success or a negative error code on failure.
> + */
> +int drm_gem_dumb_map_offset(struct drm_file *file, struct drm_device *dev,
> +			    u32 handle, u64 *offset)
> +{
> +	struct drm_gem_object *obj;
> +	int ret;
> +
> +	obj = drm_gem_object_lookup(file, handle);
> +	if (!obj)
> +		return -ENOENT;
> +
> +	ret = drm_gem_create_mmap_offset(obj);

There are 3 drm_driver->dumb_map_offset implementations that
don't call drm_gem_create_mmap_offset():
- drm_gem_cma_dumb_map_offset()
- exynos_drm_gem_dumb_map_offset()
- tegra_bo_dumb_map_offset()

They do it during object creation.

exynos have this commit:
drm/exynos: create a fake mmap offset with gem creation
48cf53f4343ae12ddc1c60dbe116161ecf7a2885

I looked at the discussion but didn't understand the rationale:
https://lists.freedesktop.org/archives/dri-devel/2015-August/088541.html

I see that it's ok to call drm_gem_create_mmap_offset() multiple times,
so it's not really a problem for this function, but it would be nice to
know why for my shmem gem library which is based on the cma library.

Noralf.


> +	if (ret)
> +		goto out;
> +
> +	*offset = drm_vma_node_offset_addr(&obj->vma_node);
> +out:
> +	drm_gem_object_put_unlocked(obj);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(drm_gem_dumb_map_offset);
> +
> +/**
>    * drm_gem_dumb_destroy - dumb fb callback helper for gem based drivers
>    * @file: drm file-private structure to remove the dumb handle from
>    * @dev: corresponding drm_device
> diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
> index 4a9d231..9c55c2a 100644
> --- a/include/drm/drm_gem.h
> +++ b/include/drm/drm_gem.h
> @@ -302,6 +302,8 @@ void drm_gem_put_pages(struct drm_gem_object *obj, struct page **pages,
>   		bool dirty, bool accessed);
>   
>   struct drm_gem_object *drm_gem_object_lookup(struct drm_file *filp, u32 handle);
> +int drm_gem_dumb_map_offset(struct drm_file *file, struct drm_device *dev,
> +			    u32 handle, u64 *offset);
>   int drm_gem_dumb_destroy(struct drm_file *file,
>   			 struct drm_device *dev,
>   			 uint32_t handle);