[PATCH 2/3] drm/prime: Support importing DMA-BUF without sg_table

oushixiong1025
2025-04-30T08:58:58Z

From: Shixiong Ou <oushixiong@kylinos.cn>

[WHY]
On some boards, the dma_mask of Aspeed devices is 0xffff_ffff, this
quite possibly causes the SWIOTLB to be triggered when importing dmabuf.
However IO_TLB_SEGSIZE limits the maximum amount of available memory
for DMA Streaming Mapping, as dmesg following:

[ 24.885303][ T1947] ast 0000:07:00.0: swiotlb buffer is full (sz: 3145728 bytes), total 32768 (slots), used 0 (slots)

[HOW] Provide an interface so that attachment is not mapped when
importing dma-buf.

Signed-off-by: Shixiong Ou <oushixiong@kylinos.cn>
---
drivers/gpu/drm/ast/ast_drv.c | 2 +-
drivers/gpu/drm/drm_gem_shmem_helper.c | 17 +++++++
drivers/gpu/drm/drm_prime.c | 67 ++++++++++++++++++++++++--
drivers/gpu/drm/udl/udl_drv.c | 2 +-
include/drm/drm_drv.h | 3 ++
include/drm/drm_gem_shmem_helper.h | 6 +++
6 files changed, 91 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/ast/ast_drv.c b/drivers/gpu/drm/ast/ast_drv.c
index 6fbf62a99c48..2dac6acf79e7 100644
--- a/drivers/gpu/drm/ast/ast_drv.c
+++ b/drivers/gpu/drm/ast/ast_drv.c
@@ -64,7 +64,7 @@ static const struct drm_driver ast_driver = {
.minor = DRIVER_MINOR,
.patchlevel = DRIVER_PATCHLEVEL,

- DRM_GEM_SHMEM_DRIVER_OPS,
+ DRM_GEM_SHMEM_SIMPLE_DRIVER_OPS,
DRM_FBDEV_SHMEM_DRIVER_OPS,
};

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index d99dee67353a..655d841df933 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -799,6 +799,23 @@ drm_gem_shmem_prime_import_sg_table(struct drm_device *dev,
}
EXPORT_SYMBOL_GPL(drm_gem_shmem_prime_import_sg_table);

+struct drm_gem_object *
+drm_gem_shmem_prime_import_attachment(struct drm_device *dev,
+ struct dma_buf_attachment *attach)
+{
+ size_t size = PAGE_ALIGN(attach->dmabuf->size);
+ struct drm_gem_shmem_object *shmem;
+
+ shmem = __drm_gem_shmem_create(dev, size, true, NULL);
+ if (IS_ERR(shmem))
+ return ERR_CAST(shmem);
+
+ drm_dbg_prime(dev, "size = %zu\n", size);
+
+ return &shmem->base;
+}
+EXPORT_SYMBOL_GPL(drm_gem_shmem_prime_import_attachment);
+
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 8e70abca33b9..522cf974e202 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -911,6 +911,62 @@ struct dma_buf *drm_gem_prime_export(struct drm_gem_object *obj,
}
EXPORT_SYMBOL(drm_gem_prime_export);

+/**
+ * drm_gem_prime_import_dev_skip_map - core implementation of the import callback
+ * @dev: drm_device to import into
+ * @dma_buf: dma-buf object to import
+ * @attach_dev: struct device to dma_buf attach
+ *
+ * This function exports a dma-buf without get it's scatter/gather table.
+ *
+ * Drivers who need to get an scatter/gather table for objects need to call
+ * drm_gem_prime_import_dev() instead.
+ */
+struct drm_gem_object *drm_gem_prime_import_dev_skip_map(struct drm_device *dev,
+ struct dma_buf *dma_buf,
+ struct device *attach_dev)
+{
+ struct dma_buf_attachment *attach;
+ struct drm_gem_object *obj;
+ int ret;
+
+ if (dma_buf->ops == &drm_gem_prime_dmabuf_ops) {
+ 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;
+ }
+ }
+
+ attach = dma_buf_attach(dma_buf, attach_dev, true);
+ if (IS_ERR(attach))
+ return ERR_CAST(attach);
+
+ get_dma_buf(dma_buf);
+
+ obj = dev->driver->gem_prime_import_attachment(dev, attach);
+ if (IS_ERR(obj)) {
+ ret = PTR_ERR(obj);
+ goto fail_detach;
+ }
+
+ obj->import_attach = attach;
+ obj->resv = dma_buf->resv;
+
+ return obj;
+
+fail_detach:
+ dma_buf_detach(dma_buf, attach);
+ dma_buf_put(dma_buf);
+
+ return ERR_PTR(ret);
+}
+EXPORT_SYMBOL(drm_gem_prime_import_dev_skip_map);
+
/**
* drm_gem_prime_import_dev - core implementation of the import callback
* @dev: drm_device to import into
@@ -946,9 +1002,6 @@ struct drm_gem_object *drm_gem_prime_import_dev(struct drm_device *dev,
}
}

- if (!dev->driver->gem_prime_import_sg_table)
- return ERR_PTR(-EINVAL);
-
attach = dma_buf_attach(dma_buf, attach_dev, false);
if (IS_ERR(attach))
return ERR_CAST(attach);
@@ -998,7 +1051,13 @@ EXPORT_SYMBOL(drm_gem_prime_import_dev);
struct drm_gem_object *drm_gem_prime_import(struct drm_device *dev,
struct dma_buf *dma_buf)
{
- return drm_gem_prime_import_dev(dev, dma_buf, dev->dev);
+ if (dev->driver->gem_prime_import_sg_table)
+ return drm_gem_prime_import_dev(dev, dma_buf, dev->dev);
+ else if (dev->driver->gem_prime_import_attachment)
+ return drm_gem_prime_import_dev_skip_map(dev, dma_buf, dev->dev);
+ else
+ return ERR_PTR(-EINVAL);
+
}
EXPORT_SYMBOL(drm_gem_prime_import);

diff --git a/drivers/gpu/drm/udl/udl_drv.c b/drivers/gpu/drm/udl/udl_drv.c
index 05b3a152cc33..c00d8b8834f2 100644
--- a/drivers/gpu/drm/udl/udl_drv.c
+++ b/drivers/gpu/drm/udl/udl_drv.c
@@ -72,7 +72,7 @@ static const struct drm_driver driver = {

/* GEM hooks */
.fops = &udl_driver_fops,
- DRM_GEM_SHMEM_DRIVER_OPS,
+ DRM_GEM_SHMEM_SIMPLE_DRIVER_OPS,
.gem_prime_import = udl_driver_gem_prime_import,
DRM_FBDEV_SHMEM_DRIVER_OPS,

diff --git a/include/drm/drm_drv.h b/include/drm/drm_drv.h
index a43d707b5f36..aef8d9051fcd 100644
--- a/include/drm/drm_drv.h
+++ b/include/drm/drm_drv.h
@@ -326,6 +326,9 @@ struct drm_driver {
struct dma_buf_attachment *attach,
struct sg_table *sgt);

+ struct drm_gem_object *(*gem_prime_import_attachment)(
+ struct drm_device *dev,
+ struct dma_buf_attachment *attach);
/**
* @dumb_create:
*
diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h
index cef5a6b5a4d6..39a93c222aaa 100644
--- a/include/drm/drm_gem_shmem_helper.h
+++ b/include/drm/drm_gem_shmem_helper.h
@@ -274,6 +274,9 @@ struct drm_gem_object *
drm_gem_shmem_prime_import_sg_table(struct drm_device *dev,
struct dma_buf_attachment *attach,
struct sg_table *sgt);
+struct drm_gem_object *
+drm_gem_shmem_prime_import_attachment(struct drm_device *dev,
+ struct dma_buf_attachment *attach);
int drm_gem_shmem_dumb_create(struct drm_file *file, struct drm_device *dev,
struct drm_mode_create_dumb *args);

@@ -287,4 +290,7 @@ 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

+#define DRM_GEM_SHMEM_SIMPLE_DRIVER_OPS \
+ .gem_prime_import_attachment = drm_gem_shmem_prime_import_attachment, \
+ .dumb_create = drm_gem_shmem_dumb_create
#endif /* __DRM_GEM_SHMEM_HELPER_H__ */
--
2.17.1