Commit 660cd446 authored by Shixiong Ou's avatar Shixiong Ou Committed by Thomas Zimmermann
Browse files

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: default avatarShixiong Ou <oushixiong@kylinos.cn>
Acked-by: default avatarThomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: default avatarThomas Zimmermann <tzimmermann@suse.de>
Link: https://lore.kernel.org/r/20250522070714.439824-1-oushixiong1025@163.com
parent 6048f558

drivers/gpu/drm/drm_gem_shmem_helper.c

+57 −0
Original line number Diff line number Diff line
@@ -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");

drivers/gpu/drm/drm_prime.c

+27 −9
Original line number Diff line number Diff line
@@ -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
@@ -951,17 +971,15 @@ 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) {

		obj = dma_buf->priv;

		if (obj->dev == dev) {

	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;

	}

	}



	if (!dev->driver->gem_prime_import_sg_table)

		return ERR_PTR(-EINVAL);

include/drm/drm_gem_shmem_helper.h

+15 −0
Original line number Diff line number Diff line
@@ -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__ */

include/drm/drm_prime.h

+3 −0
Original line number Diff line number Diff line
@@ -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);