drm/gem: Test for imported GEM buffers with helper

Add drm_gem_is_imported() that tests if a GEM object's buffer has
been imported. Update the GEM code accordingly.

GEM code usually tests for imports if import_attach has been set
in struct drm_gem_object. But attaching a dma-buf on import requires
a DMA-capable importer device, which is not the case for many serial
busses like USB or I2C. The new helper tests if a GEM object's dma-buf
has been created from the GEM object.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Anusha Srivatsa <asrivats@redhat.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250226172457.217725-2-tzimmermann@suse.de

drivers/gpu/drm/drm_gem.c

@@ -348,7 +348,7 @@ int drm_gem_dumb_map_offset(struct drm_file *file, struct drm_device *dev,
 		return -ENOENT;
 
 	/* Don't allow imported objects to be mapped */
-	if (obj->import_attach) {
+	if (drm_gem_is_imported(obj)) {
 		ret = -EINVAL;
 		goto out;
 	}
@@ -1178,7 +1178,7 @@ void drm_gem_print_info(struct drm_printer *p, unsigned int indent,
 			  drm_vma_node_start(&obj->vma_node));
 	drm_printf_indent(p, indent, "size=%zu\n", obj->size);
 	drm_printf_indent(p, indent, "imported=%s\n",
-			  str_yes_no(obj->import_attach));
+			  str_yes_no(drm_gem_is_imported(obj)));
 
 	if (obj->funcs->print_info)
 		obj->funcs->print_info(p, indent, obj);

include/drm/drm_gem.h

@@ -35,6 +35,7 @@
  */
 
 #include <linux/kref.h>
+#include <linux/dma-buf.h>
 #include <linux/dma-resv.h>
 #include <linux/list.h>
 #include <linux/mutex.h>
@@ -575,6 +576,19 @@ static inline bool drm_gem_object_is_shared_for_memory_stats(struct drm_gem_obje
 	return (obj->handle_count > 1) || obj->dma_buf;
 }
 
+/**
+ * drm_gem_is_imported() - Tests if GEM object's buffer has been imported
+ * @obj: the GEM object
+ *
+ * Returns:
+ * True if the GEM object's buffer has been imported, false otherwise
+ */
+static inline bool drm_gem_is_imported(const struct drm_gem_object *obj)
+{
+	/* The dma-buf's priv field points to the original GEM object. */
+	return obj->dma_buf && (obj->dma_buf->priv != obj);
+}
+
 #ifdef CONFIG_LOCKDEP
 /**
  * drm_gem_gpuva_set_lock() - Set the lock protecting accesses to the gpuva list.