[PATCH v4 03/13] drm/cma-helper: Provide a vmap function for short-term mappings

Thomas Zimmermann
2021-01-08T09:43:30Z

Implementations of the vmap/vunmap GEM callbacks may perform pinning
of the BO and may acquire the associated reservation object's lock.
Callers that only require a mapping of the contained memory can thus
interfere with other tasks that require exact pinning, such as scanout.
This is less of an issue with private CMA buffers, but may happen
with imported ones.

Therefore provide the new interface drm_gem_cma_vmap_local(), which only
performs the vmap operations. Callers have to hold the reservation lock
while the mapping persists.

This patch also connects GEM CMA helpers to the GEM object function with
equivalent functionality.

v4:
	* vc4: don't wrap drm_gem_cma_vmap_local() in BO funcs (Daniel)
	* remove the TODO comment (Daniel)

Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
---
 drivers/gpu/drm/drm_gem_cma_helper.c | 27 +++++++++++++++++++++++++++
 drivers/gpu/drm/vc4/vc4_bo.c         |  1 +
 include/drm/drm_gem_cma_helper.h     |  1 +
 3 files changed, 29 insertions(+)

diff --git a/drivers/gpu/drm/drm_gem_cma_helper.c
b/drivers/gpu/drm/drm_gem_cma_helper.c
index 7942cf05cd93..f854027fa01f 100644
--- a/drivers/gpu/drm/drm_gem_cma_helper.c
+++ b/drivers/gpu/drm/drm_gem_cma_helper.c
@@ -38,6 +38,7 @@ static const struct drm_gem_object_funcs
drm_gem_cma_default_funcs = {
 	.print_info = drm_gem_cma_print_info,
 	.get_sg_table = drm_gem_cma_get_sg_table,
 	.vmap = drm_gem_cma_vmap,
+	.vmap_local = drm_gem_cma_vmap_local,
 	.mmap = drm_gem_cma_mmap,
 	.vm_ops = &drm_gem_cma_vm_ops,
 };
@@ -471,6 +472,32 @@ int drm_gem_cma_vmap(struct drm_gem_object *obj, struct
dma_buf_map *map)
 }
 EXPORT_SYMBOL_GPL(drm_gem_cma_vmap);

+/**
+ * drm_gem_cma_vmap_local - map a CMA GEM object into the kernel's virtual
+ *     address space
+ * @obj: GEM object
+ * @map: Returns the kernel virtual address of the CMA GEM object's backing
+ *       store.
+ *
+ * This function maps a buffer into the kernel's
+ * virtual address space. Since the CMA buffers are already mapped into the
+ * kernel virtual address space this simply returns the cached virtual
+ * address. Drivers using the CMA helpers should set this as their DRM
+ * driver's &drm_gem_object_funcs.vmap_local callback.
+ *
+ * Returns:
+ * 0 on success, or a negative error code otherwise.
+ */
+int drm_gem_cma_vmap_local(struct drm_gem_object *obj, struct dma_buf_map *map)
+{
+	struct drm_gem_cma_object *cma_obj = to_drm_gem_cma_obj(obj);
+
+	dma_buf_map_set_vaddr(map, cma_obj->vaddr);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(drm_gem_cma_vmap_local);
+
 /**
  * drm_gem_cma_mmap - memory-map an exported CMA GEM object
  * @obj: GEM object
diff --git a/drivers/gpu/drm/vc4/vc4_bo.c b/drivers/gpu/drm/vc4/vc4_bo.c
index dc316cb79e00..7283c018dbaf 100644
--- a/drivers/gpu/drm/vc4/vc4_bo.c
+++ b/drivers/gpu/drm/vc4/vc4_bo.c
@@ -387,6 +387,7 @@ static const struct drm_gem_object_funcs
vc4_gem_object_funcs = {
 	.export = vc4_prime_export,
 	.get_sg_table = drm_gem_cma_get_sg_table,
 	.vmap = vc4_prime_vmap,
+	.vmap_local = drm_gem_cma_vmap_local,
 	.vm_ops = &vc4_vm_ops,
 };

diff --git a/include/drm/drm_gem_cma_helper.h b/include/drm/drm_gem_cma_helper.h
index 0a9711caa3e8..05122e71bc6d 100644
--- a/include/drm/drm_gem_cma_helper.h
+++ b/include/drm/drm_gem_cma_helper.h
@@ -99,6 +99,7 @@ drm_gem_cma_prime_import_sg_table(struct drm_device *dev,
 				  struct dma_buf_attachment *attach,
 				  struct sg_table *sgt);
 int drm_gem_cma_vmap(struct drm_gem_object *obj, struct dma_buf_map *map);
+int drm_gem_cma_vmap_local(struct drm_gem_object *obj, struct dma_buf_map
*map);
 int drm_gem_cma_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma);

 /**
--
2.29.2