Commit 37a48adf authored by Thomas Zimmermann's avatar Thomas Zimmermann
Browse files

drm/vram: Add kmap ref-counting to GEM VRAM objects 



The kmap and kunmap operations of GEM VRAM buffers can now be called
in interleaving pairs. The first call to drm_gem_vram_kmap() maps the
buffer's memory to kernel address space and the final call to
drm_gem_vram_kunmap() unmaps the memory. Intermediate calls to these
functions increment or decrement a reference counter.

This change allows for keeping buffer memory mapped for longer and
minimizes the amount of changes to TLB, page tables, etc.

v4:
	* lock in kmap()/kunmap() with ttm_bo_reserve()

Signed-off-by: default avatarThomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: default avatarGerd Hoffmann <kraxel@redhat.com>
Acked-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
Reported-and-tested-by: default avatarDavidlohr Bueso <dbueso@suse.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20190906122056.32018-2-tzimmermann@suse.de
parent e5ef909c

drivers/gpu/drm/drm_gem_vram_helper.c

+57 −18
Original line number Diff line number Diff line
@@ -26,6 +26,9 @@ static void drm_gem_vram_cleanup(struct drm_gem_vram_object *gbo) 
	 * TTM buffer object in 'bo' has already been cleaned

	 * up; only release the GEM object.

	 */



	WARN_ON(gbo->kmap_use_count);



	drm_gem_object_release(&gbo->bo.base);

}
@@ -283,6 +286,34 @@ err_ttm_bo_unreserve: 
}

EXPORT_SYMBOL(drm_gem_vram_unpin);



static void *drm_gem_vram_kmap_locked(struct drm_gem_vram_object *gbo,

				      bool map, bool *is_iomem)

{

	int ret;

	struct ttm_bo_kmap_obj *kmap = &gbo->kmap;



	if (gbo->kmap_use_count > 0)

		goto out;



	if (kmap->virtual || !map)

		goto out;



	ret = ttm_bo_kmap(&gbo->bo, 0, gbo->bo.num_pages, kmap);

	if (ret)

		return ERR_PTR(ret);



out:

	if (!kmap->virtual) {

		if (is_iomem)

			*is_iomem = false;

		return NULL; /* not mapped; don't increment ref */

	}

	++gbo->kmap_use_count;

	if (is_iomem)

		return ttm_kmap_obj_virtual(kmap, is_iomem);

	return kmap->virtual;

}



/**

 * drm_gem_vram_kmap() - Maps a GEM VRAM object into kernel address space

 * @gbo:	the GEM VRAM object
@@ -304,40 +335,48 @@ void *drm_gem_vram_kmap(struct drm_gem_vram_object *gbo, bool map, 
			bool *is_iomem)

{

	int ret;

	struct ttm_bo_kmap_obj *kmap = &gbo->kmap;

	void *virtual;



	if (kmap->virtual || !map)

		goto out;



	ret = ttm_bo_kmap(&gbo->bo, 0, gbo->bo.num_pages, kmap);

	ret = ttm_bo_reserve(&gbo->bo, true, false, NULL);

	if (ret)

		return ERR_PTR(ret);

	virtual = drm_gem_vram_kmap_locked(gbo, map, is_iomem);

	ttm_bo_unreserve(&gbo->bo);



out:

	if (!is_iomem)

		return kmap->virtual;

	if (!kmap->virtual) {

		*is_iomem = false;

		return NULL;

	}

	return ttm_kmap_obj_virtual(kmap, is_iomem);

	return virtual;

}

EXPORT_SYMBOL(drm_gem_vram_kmap);



/**

 * drm_gem_vram_kunmap() - Unmaps a GEM VRAM object

 * @gbo:	the GEM VRAM object

 */

void drm_gem_vram_kunmap(struct drm_gem_vram_object *gbo)

static void drm_gem_vram_kunmap_locked(struct drm_gem_vram_object *gbo)

{

	struct ttm_bo_kmap_obj *kmap = &gbo->kmap;



	if (WARN_ON_ONCE(!gbo->kmap_use_count))

		return;

	if (--gbo->kmap_use_count > 0)

		return;



	if (!kmap->virtual)

		return;



	ttm_bo_kunmap(kmap);

	kmap->virtual = NULL;

}



/**

 * drm_gem_vram_kunmap() - Unmaps a GEM VRAM object

 * @gbo:	the GEM VRAM object

 */

void drm_gem_vram_kunmap(struct drm_gem_vram_object *gbo)

{

	int ret;



	ret = ttm_bo_reserve(&gbo->bo, false, false, NULL);

	if (WARN_ONCE(ret, "ttm_bo_reserve_failed(): ret=%d\n", ret))

		return;

	drm_gem_vram_kunmap_locked(gbo);

	ttm_bo_unreserve(&gbo->bo);

}

EXPORT_SYMBOL(drm_gem_vram_kunmap);



/**

include/drm/drm_gem_vram_helper.h

+14 −0
Original line number Diff line number Diff line
@@ -34,11 +34,25 @@ struct vm_area_struct; 
 * backed by VRAM. It can be used for simple framebuffer devices with

 * dedicated memory. The buffer object can be evicted to system memory if

 * video memory becomes scarce.

 *

 * GEM VRAM objects perform reference counting for pin and mapping

 * operations. So a buffer object that has been pinned N times with

 * drm_gem_vram_pin() must be unpinned N times with

 * drm_gem_vram_unpin(). The same applies to pairs of

 * drm_gem_vram_kmap() and drm_gem_vram_kunmap().

 */

struct drm_gem_vram_object {

	struct ttm_buffer_object bo;

	struct ttm_bo_kmap_obj kmap;



	/**

	 * @kmap_use_count:

	 *

	 * Reference count on the virtual address.

	 * The address are un-mapped when the count reaches zero.

	 */

	unsigned int kmap_use_count;



	/* Supported placements are %TTM_PL_VRAM and %TTM_PL_SYSTEM */

	struct ttm_placement placement;

	struct ttm_place placements[2];

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