drm/gem: Inline drm_gem_pin() into PRIME helpers

Inline drm_gem_pin() into its only caller drm_gem_map_attach()
and update the documentation in the callback's purpose. Do the
equivalent for drm_gem_unpin(). Also add stricter error checking
on the involved locking.

The pin operation in the GEM object functions is a helper for
PRIME-exported buffer objects. Having drm_gem_pin() gives the
impression of a general-purpose interface, which is not the case.
Removing it makes the pin callback a bit harder to misuse.

v2:
- clarify comment on pin callback (Dmitry)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Link: https://lore.kernel.org/r/20250526132634.531789-5-tzimmermann@suse.de

drivers/gpu/drm/drm_gem.c

@@ -1184,38 +1184,6 @@ void drm_gem_print_info(struct drm_printer *p, unsigned int indent,
 		obj->funcs->print_info(p, indent, obj);
 }
 
-int drm_gem_pin_locked(struct drm_gem_object *obj)
-{
-	if (obj->funcs->pin)
-		return obj->funcs->pin(obj);
-
-	return 0;
-}
-
-void drm_gem_unpin_locked(struct drm_gem_object *obj)
-{
-	if (obj->funcs->unpin)
-		obj->funcs->unpin(obj);
-}
-
-int drm_gem_pin(struct drm_gem_object *obj)
-{
-	int ret;
-
-	dma_resv_lock(obj->resv, NULL);
-	ret = drm_gem_pin_locked(obj);
-	dma_resv_unlock(obj->resv);
-
-	return ret;
-}
-
-void drm_gem_unpin(struct drm_gem_object *obj)
-{
-	dma_resv_lock(obj->resv, NULL);
-	drm_gem_unpin_locked(obj);
-	dma_resv_unlock(obj->resv);
-}
-
 int drm_gem_vmap_locked(struct drm_gem_object *obj, struct iosys_map *map)
 {
 	int ret;

drivers/gpu/drm/drm_internal.h

@@ -175,10 +175,6 @@ void drm_gem_release(struct drm_device *dev, struct drm_file *file_private);
 void drm_gem_print_info(struct drm_printer *p, unsigned int indent,
 			const struct drm_gem_object *obj);
 
-int drm_gem_pin_locked(struct drm_gem_object *obj);
-void drm_gem_unpin_locked(struct drm_gem_object *obj);
-int drm_gem_pin(struct drm_gem_object *obj);
-void drm_gem_unpin(struct drm_gem_object *obj);
 int drm_gem_vmap_locked(struct drm_gem_object *obj, struct iosys_map *map);
 void drm_gem_vunmap_locked(struct drm_gem_object *obj, struct iosys_map *map);
 

drivers/gpu/drm/drm_prime.c

@@ -599,6 +599,7 @@ int drm_gem_map_attach(struct dma_buf *dma_buf,
 		       struct dma_buf_attachment *attach)
 {
 	struct drm_gem_object *obj = dma_buf->priv;
+	int ret;
 
 	/*
 	 * drm_gem_map_dma_buf() requires obj->get_sg_table(), but drivers
@@ -608,7 +609,16 @@ int drm_gem_map_attach(struct dma_buf *dma_buf,
 	    !obj->funcs->get_sg_table)
 		return -ENOSYS;
 
-	return drm_gem_pin(obj);
+	if (!obj->funcs->pin)
+		return 0;
+
+	ret = dma_resv_lock(obj->resv, NULL);
+	if (ret)
+		return ret;
+	ret = obj->funcs->pin(obj);
+	dma_resv_unlock(obj->resv);
+
+	return ret;
 }
 EXPORT_SYMBOL(drm_gem_map_attach);
 
@@ -625,8 +635,16 @@ void drm_gem_map_detach(struct dma_buf *dma_buf,
 			struct dma_buf_attachment *attach)
 {
 	struct drm_gem_object *obj = dma_buf->priv;
+	int ret;
 
-	drm_gem_unpin(obj);
+	if (!obj->funcs->unpin)
+		return;
+
+	ret = dma_resv_lock(obj->resv, NULL);
+	if (drm_WARN_ON(obj->dev, ret))
+		return;
+	obj->funcs->unpin(obj);
+	dma_resv_unlock(obj->resv);
 }
 EXPORT_SYMBOL(drm_gem_map_detach);
 

include/drm/drm_gem.h

@@ -126,7 +126,8 @@ struct drm_gem_object_funcs {
 	/**
 	 * @pin:
 	 *
-	 * Pin backing buffer in memory. Used by the drm_gem_map_attach() helper.
+	 * Pin backing buffer in memory, such that dma-buf importers can
+	 * access it. Used by the drm_gem_map_attach() helper.
 	 *
 	 * This callback is optional.
 	 */