[PATCH v4 09/13] drm/vram-helper: Provide a vmap function for short-term mappings

Thomas Zimmermann
2021-01-08T09:43:36Z

Implementations of the vmap/vunmap GEM callbacks may perform pinning
of the BO and may acquire the associated reservation object's lock.
It's somewhat inconvenient to callers that simply require a mapping of
the contained memory; and also ipmplies a certain overhead.

Therefore provide drm_gem_vram_vmap_local() drm_gem_vram_vunmap_local(),
which only perform the vmap/vunmap operations. Callers have to hold the
reservation lock while the mapping persists; or have to pin the BO by
themselves.

This patch connects GEM VRAM helpers to GEM object functions with
equivalent functionality.

v4:
	* move driver changes into separate patches (Daniel)
	* update documentation (Daniel)

Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
---
 drivers/gpu/drm/drm_gem_vram_helper.c | 141 +++++++++++++++++---------
 include/drm/drm_gem_vram_helper.h     |   2 +
 2 files changed, 95 insertions(+), 48 deletions(-)

diff --git a/drivers/gpu/drm/drm_gem_vram_helper.c
b/drivers/gpu/drm/drm_gem_vram_helper.c
index 02ca22e90290..c7fba3a0758e 100644
--- a/drivers/gpu/drm/drm_gem_vram_helper.c
+++ b/drivers/gpu/drm/drm_gem_vram_helper.c
@@ -379,47 +379,6 @@ int drm_gem_vram_unpin(struct drm_gem_vram_object *gbo)
 }
 EXPORT_SYMBOL(drm_gem_vram_unpin);

-static int drm_gem_vram_kmap_locked(struct drm_gem_vram_object *gbo,
-				    struct dma_buf_map *map)
-{
-	int ret;
-
-	if (gbo->vmap_use_count > 0)
-		goto out;
-
-	ret = ttm_bo_vmap(&gbo->bo, &gbo->map);
-	if (ret)
-		return ret;
-
-out:
-	++gbo->vmap_use_count;
-	*map = gbo->map;
-
-	return 0;
-}
-
-static void drm_gem_vram_kunmap_locked(struct drm_gem_vram_object *gbo,
-				       struct dma_buf_map *map)
-{
-	struct drm_device *dev = gbo->bo.base.dev;
-
-	if (drm_WARN_ON_ONCE(dev, !gbo->vmap_use_count))
-		return;
-
-	if (drm_WARN_ON_ONCE(dev, !dma_buf_map_is_equal(&gbo->map, map)))
-		return; /* BUG: map not mapped from this BO */
-
-	if (--gbo->vmap_use_count > 0)
-		return;
-
-	/*
-	 * Permanently mapping and unmapping buffers adds overhead from
-	 * updating the page tables and creates debugging output. Therefore,
-	 * we delay the actual unmap operation until the BO gets evicted
-	 * from memory. See drm_gem_vram_bo_driver_move_notify().
-	 */
-}
-
 /**
  * drm_gem_vram_vmap() - Pins and maps a GEM VRAM object into kernel address
  *                       space
@@ -447,7 +406,7 @@ int drm_gem_vram_vmap(struct drm_gem_vram_object *gbo,
struct dma_buf_map *map)
 	ret = drm_gem_vram_pin_locked(gbo, 0);
 	if (ret)
 		goto err_ttm_bo_unreserve;
-	ret = drm_gem_vram_kmap_locked(gbo, map);
+	ret = drm_gem_vram_vmap_local(gbo, map);
 	if (ret)
 		goto err_drm_gem_vram_unpin_locked;

@@ -479,13 +438,83 @@ void drm_gem_vram_vunmap(struct drm_gem_vram_object *gbo,
struct dma_buf_map *ma
 	if (WARN_ONCE(ret, "ttm_bo_reserve_failed(): ret=%d\n", ret))
 		return;

-	drm_gem_vram_kunmap_locked(gbo, map);
+	drm_gem_vram_vunmap_local(gbo, map);
 	drm_gem_vram_unpin_locked(gbo);

 	ttm_bo_unreserve(&gbo->bo);
 }
 EXPORT_SYMBOL(drm_gem_vram_vunmap);

+/**
+ * drm_gem_vram_vmap_local() - Maps a GEM VRAM object into kernel address space
+ * @gbo: The GEM VRAM object to map
+ * @map: Returns the kernel virtual address of the VRAM GEM object's
backing
+ *       store.
+ *
+ * The vmap_local function maps the buffer of a GEM VRAM object into kernel
address
+ * space. Call drm_gem_vram_vunmap_local() with the returned address to unmap
and
+ * unpin the GEM VRAM object.
+ *
+ * The function is called with the BO's reservation object locked. For
short-term
+ * mappings, callers must hold the BO's reservation lock until after
unmapping the
+ * buffer.
+ *
+ * Returns:
+ * 0 on success, or a negative error code otherwise.
+ */
+int drm_gem_vram_vmap_local(struct drm_gem_vram_object *gbo, struct dma_buf_map
*map)
+{
+	int ret;
+
+	dma_resv_assert_held(gbo->bo.base.resv);
+
+	if (gbo->vmap_use_count > 0)
+		goto out;
+
+	ret = ttm_bo_vmap(&gbo->bo, &gbo->map);
+	if (ret)
+		return ret;
+
+out:
+	++gbo->vmap_use_count;
+	*map = gbo->map;
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_gem_vram_vmap_local);
+
+/**
+ * drm_gem_vram_vunmap_local() - Unmaps a GEM VRAM object
+ * @gbo: The GEM VRAM object to unmap
+ * @map: Kernel virtual address where the VRAM GEM object was mapped
+ *
+ * A call to drm_gem_vram_vunmap_local() unmaps a GEM VRAM object's buffer.
See
+ * the documentation for drm_gem_vram_vmap_local() for more information.
+ */
+void drm_gem_vram_vunmap_local(struct drm_gem_vram_object *gbo, struct
dma_buf_map *map)
+{
+	struct drm_device *dev = gbo->bo.base.dev;
+
+	dma_resv_assert_held(gbo->bo.base.resv);
+
+	if (drm_WARN_ON_ONCE(dev, !gbo->vmap_use_count))
+		return;
+
+	if (drm_WARN_ON_ONCE(dev, !dma_buf_map_is_equal(&gbo->map, map)))
+		return; /* BUG: map not mapped from this BO */
+
+	if (--gbo->vmap_use_count > 0)
+		return;
+
+	/*
+	 * Permanently mapping and unmapping buffers adds overhead from
+	 * updating the page tables and creates debugging output. Therefore,
+	 * we delay the actual unmap operation until the BO gets evicted
+	 * from memory. See drm_gem_vram_bo_driver_move_notify().
+	 */
+}
+EXPORT_SYMBOL(drm_gem_vram_vunmap_local);
+
 /**
  * drm_gem_vram_fill_create_dumb() - \
 	Helper for implementing &struct drm_driver.dumb_create
@@ -871,17 +900,33 @@ static void drm_gem_vram_object_vunmap(struct
drm_gem_object *gem, struct dma_bu
 	drm_gem_vram_vunmap(gbo, map);
 }

+static int drm_gem_vram_object_vmap_local(struct drm_gem_object *gem, struct
dma_buf_map *map)
+{
+	struct drm_gem_vram_object *gbo = drm_gem_vram_of_gem(gem);
+
+	return drm_gem_vram_vmap_local(gbo, map);
+}
+
+static void drm_gem_vram_object_vunmap_local(struct drm_gem_object *gem, struct
dma_buf_map *map)
+{
+	struct drm_gem_vram_object *gbo = drm_gem_vram_of_gem(gem);
+
+	drm_gem_vram_vunmap_local(gbo, map);
+}
+
 /*
  * GEM object funcs
  */

 static const struct drm_gem_object_funcs drm_gem_vram_object_funcs = {
-	.free	= drm_gem_vram_object_free,
-	.pin	= drm_gem_vram_object_pin,
-	.unpin	= drm_gem_vram_object_unpin,
-	.vmap	= drm_gem_vram_object_vmap,
+	.free = drm_gem_vram_object_free,
+	.pin = drm_gem_vram_object_pin,
+	.unpin = drm_gem_vram_object_unpin,
+	.vmap = drm_gem_vram_object_vmap,
 	.vunmap	= drm_gem_vram_object_vunmap,
-	.mmap   = drm_gem_ttm_mmap,
+	.vmap_local = drm_gem_vram_object_vmap_local,
+	.vunmap_local = drm_gem_vram_object_vunmap_local,
+	.mmap = drm_gem_ttm_mmap,
 	.print_info = drm_gem_ttm_print_info,
 };

diff --git a/include/drm/drm_gem_vram_helper.h
b/include/drm/drm_gem_vram_helper.h
index a4bac02249c2..bd6a60e7c22b 100644
--- a/include/drm/drm_gem_vram_helper.h
+++ b/include/drm/drm_gem_vram_helper.h
@@ -99,6 +99,8 @@ int drm_gem_vram_pin(struct drm_gem_vram_object *gbo, unsigned
long pl_flag);
 int drm_gem_vram_unpin(struct drm_gem_vram_object *gbo);
 int drm_gem_vram_vmap(struct drm_gem_vram_object *gbo, struct dma_buf_map
*map);
 void drm_gem_vram_vunmap(struct drm_gem_vram_object *gbo, struct dma_buf_map
*map);
+int drm_gem_vram_vmap_local(struct drm_gem_vram_object *gbo, struct dma_buf_map
*map);
+void drm_gem_vram_vunmap_local(struct drm_gem_vram_object *gbo, struct
dma_buf_map *map);

 int drm_gem_vram_fill_create_dumb(struct drm_file *file,
 				  struct drm_device *dev,
--
2.29.2