drm/shmem-helper: Import dmabuf without mapping its sg_table

[WHY]
1. Drivers using DRM_GEM_SHADOW_PLANE_HELPER_FUNCS and
   DRM_GEM_SHMEM_DRIVER_OPS (e.g., udl, ast) do not require
   sg_table import.
   They only need dma_buf_vmap() to access the shared buffer's
   kernel virtual address.

2. On certain Aspeed-based boards, a dma_mask of 0xffff_ffff may
   trigger SWIOTLB during dmabuf import. However, IO_TLB_SEGSIZE
   restricts the maximum DMA streaming mapping memory, resulting in
   errors like:

   ast 0000:07:00.0: swiotlb buffer is full (sz: 3145728 bytes), total 32768 (slots), used 0 (slots)

[HOW]
Provide a gem_prime_import implementation without sg_table mapping
to avoid issues (e.g., "swiotlb buffer is full"). Drivers that do not
require sg_table can adopt this.

Signed-off-by: Shixiong Ou <oushixiong@kylinos.cn>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://lore.kernel.org/r/20250522070714.439824-1-oushixiong1025@163.com

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index 0b41f0346bad159252980a9545cd643a79e7bf41..8ac0b1fa5287a0fb70d81559cd49a49ab5d343d6 100644 (file)
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -804,6 +804,63 @@ drm_gem_shmem_prime_import_sg_table(struct drm_device *dev,
 }
 EXPORT_SYMBOL_GPL(drm_gem_shmem_prime_import_sg_table);
 
+/**
+ * drm_gem_shmem_prime_import_no_map - Import dmabuf without mapping its sg_table
+ * @dev: Device to import into
+ * @dma_buf: dma-buf object to import
+ *
+ * Drivers that use the shmem helpers but also wants to import dmabuf without
+ * mapping its sg_table can use this as their &drm_driver.gem_prime_import
+ * implementation.
+ */
+struct drm_gem_object *drm_gem_shmem_prime_import_no_map(struct drm_device *dev,
+                                                        struct dma_buf *dma_buf)
+{
+       struct dma_buf_attachment *attach;
+       struct drm_gem_shmem_object *shmem;
+       struct drm_gem_object *obj;
+       size_t size;
+       int ret;
+
+       if (drm_gem_is_prime_exported_dma_buf(dev, dma_buf)) {
+               /*
+                * Importing dmabuf exported from our own gem increases
+                * refcount on gem itself instead of f_count of dmabuf.
+                */
+               obj = dma_buf->priv;
+               drm_gem_object_get(obj);
+               return obj;
+       }
+
+       attach = dma_buf_attach(dma_buf, dev->dev);
+       if (IS_ERR(attach))
+               return ERR_CAST(attach);
+
+       get_dma_buf(dma_buf);
+
+       size = PAGE_ALIGN(attach->dmabuf->size);
+
+       shmem = __drm_gem_shmem_create(dev, size, true, NULL);
+       if (IS_ERR(shmem)) {
+               ret = PTR_ERR(shmem);
+               goto fail_detach;
+       }
+
+       drm_dbg_prime(dev, "size = %zu\n", size);
+
+       shmem->base.import_attach = attach;
+       shmem->base.resv = dma_buf->resv;
+
+       return &shmem->base;
+
+fail_detach:
+       dma_buf_detach(dma_buf, attach);
+       dma_buf_put(dma_buf);
+
+       return ERR_PTR(ret);
+}
+EXPORT_SYMBOL_GPL(drm_gem_shmem_prime_import_no_map);
+
 MODULE_DESCRIPTION("DRM SHMEM memory-management helpers");
 MODULE_IMPORT_NS("DMA_BUF");
 MODULE_LICENSE("GPL v2");

diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index a1852c02f5123f165c0073e73fc98d5c99f37414..b703f83874e13f57f5192a03e8a0a725d4b8bd13 100644 (file)
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -928,6 +928,26 @@ struct dma_buf *drm_gem_prime_export(struct drm_gem_object *obj,
 }
 EXPORT_SYMBOL(drm_gem_prime_export);
 
+
+/**
+ * drm_gem_is_prime_exported_dma_buf -
+ * checks if the DMA-BUF was exported from a GEM object belonging to @dev.
+ * @dev: drm_device to check against
+ * @dma_buf: dma-buf object to import
+ *
+ * Return: true if the DMA-BUF was exported from a GEM object belonging
+ * to @dev, false otherwise.
+ */
+
+bool drm_gem_is_prime_exported_dma_buf(struct drm_device *dev,
+                                      struct dma_buf *dma_buf)
+{
+       struct drm_gem_object *obj = dma_buf->priv;
+
+       return (dma_buf->ops == &drm_gem_prime_dmabuf_ops) && (obj->dev == dev);
+}
+EXPORT_SYMBOL(drm_gem_is_prime_exported_dma_buf);
+
 /**
  * drm_gem_prime_import_dev - core implementation of the import callback
  * @dev: drm_device to import into
@@ -951,16 +971,14 @@ struct drm_gem_object *drm_gem_prime_import_dev(struct drm_device *dev,
        struct drm_gem_object *obj;
        int ret;
 
-       if (dma_buf->ops == &drm_gem_prime_dmabuf_ops) {
+       if (drm_gem_is_prime_exported_dma_buf(dev, dma_buf)) {
+               /*
+                * Importing dmabuf exported from our own gem increases
+                * refcount on gem itself instead of f_count of dmabuf.
+                */
                obj = dma_buf->priv;
-               if (obj->dev == dev) {
-                       /*
-                        * Importing dmabuf exported from our own gem increases
-                        * refcount on gem itself instead of f_count of dmabuf.
-                        */
-                       drm_gem_object_get(obj);
-                       return obj;
-               }
+               drm_gem_object_get(obj);
+               return obj;
        }
 
        if (!dev->driver->gem_prime_import_sg_table)

diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h
index b4f993da3caec83ae17208be13f7c80b18d04e0d..35f7466dca8480864612083f54e9037fa7373900 100644 (file)
--- a/include/drm/drm_gem_shmem_helper.h
+++ b/include/drm/drm_gem_shmem_helper.h
@@ -287,6 +287,8 @@ drm_gem_shmem_prime_import_sg_table(struct drm_device *dev,
                                    struct sg_table *sgt);
 int drm_gem_shmem_dumb_create(struct drm_file *file, struct drm_device *dev,
                              struct drm_mode_create_dumb *args);
+struct drm_gem_object *drm_gem_shmem_prime_import_no_map(struct drm_device *dev,
+                                                        struct dma_buf *buf);
 
 /**
  * DRM_GEM_SHMEM_DRIVER_OPS - Default shmem GEM operations
@@ -298,4 +300,17 @@ int drm_gem_shmem_dumb_create(struct drm_file *file, struct drm_device *dev,
        .gem_prime_import_sg_table = drm_gem_shmem_prime_import_sg_table, \
        .dumb_create               = drm_gem_shmem_dumb_create
 
+/**
+ * DRM_GEM_SHMEM_DRIVER_OPS_NO_MAP_SGT - shmem GEM operations
+ *                                       without mapping sg_table on
+ *                                       imported buffer.
+ *
+ * This macro provides a shortcut for setting the shmem GEM operations in
+ * the &drm_driver structure for drivers that do not require a sg_table on
+ * imported buffers.
+ */
+#define DRM_GEM_SHMEM_DRIVER_OPS_NO_MAP_SGT \
+       .gem_prime_import       = drm_gem_shmem_prime_import_no_map, \
+       .dumb_create            = drm_gem_shmem_dumb_create
+
 #endif /* __DRM_GEM_SHMEM_HELPER_H__ */

diff --git a/include/drm/drm_prime.h b/include/drm/drm_prime.h
index fa085c44d4ca463b964e1929917fdceac0b19654..f50f862f0d8b022369c088a70627294903a53329 100644 (file)
--- a/include/drm/drm_prime.h
+++ b/include/drm/drm_prime.h
@@ -100,6 +100,9 @@ struct dma_buf *drm_gem_prime_export(struct drm_gem_object *obj,
 unsigned long drm_prime_get_contiguous_size(struct sg_table *sgt);
 
 /* helper functions for importing */
+bool drm_gem_is_prime_exported_dma_buf(struct drm_device *dev,
+                                      struct dma_buf *dma_buf);
+
 struct drm_gem_object *drm_gem_prime_import_dev(struct drm_device *dev,
                                                struct dma_buf *dma_buf,
                                                struct device *attach_dev);