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Message-Id: <20250501064324.398650-1-oushixiong1025@163.com>
Date: Thu, 1 May 2025 14:43:22 +0800
From: oushixiong1025@....com
To: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
Cc: Maxime Ripard <mripard@...nel.org>,
Thomas Zimmermann <tzimmermann@...e.de>,
David Airlie <airlied@...il.com>,
Simona Vetter <simona@...ll.ch>,
Sean Paul <sean@...rly.run>,
Jocelyn Falempe <jfalempe@...hat.com>,
dri-devel@...ts.freedesktop.org,
linux-kernel@...r.kernel.org,
Shixiong Ou <oushixiong@...inos.cn>
Subject: [PATCH 1/3] drm/shmem-helper: Import dmabuf without mapping its sg_table
From: Shixiong Ou <oushixiong@...inos.cn>
[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@...inos.cn>
---
drivers/gpu/drm/drm_gem_shmem_helper.c | 95 ++++++++++++++++++++++++++
include/drm/drm_gem_shmem_helper.h | 24 +++++++
2 files changed, 119 insertions(+)
diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index d99dee67353a..9e41e350ff6f 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -39,6 +39,7 @@ MODULE_IMPORT_NS("DMA_BUF");
static const struct drm_gem_object_funcs drm_gem_shmem_funcs = {
.free = drm_gem_shmem_object_free,
.print_info = drm_gem_shmem_object_print_info,
+ .export = drm_gem_shmem_object_prime_export,
.pin = drm_gem_shmem_object_pin,
.unpin = drm_gem_shmem_object_unpin,
.get_sg_table = drm_gem_shmem_object_get_sg_table,
@@ -799,6 +800,100 @@ drm_gem_shmem_prime_import_sg_table(struct drm_device *dev,
}
EXPORT_SYMBOL_GPL(drm_gem_shmem_prime_import_sg_table);
+const struct dma_buf_ops drm_gem_shmem_prime_dmabuf_ops = {
+ .cache_sgt_mapping = true,
+ .attach = drm_gem_map_attach,
+ .detach = drm_gem_map_detach,
+ .map_dma_buf = drm_gem_map_dma_buf,
+ .unmap_dma_buf = drm_gem_unmap_dma_buf,
+ .release = drm_gem_dmabuf_release,
+ .mmap = drm_gem_dmabuf_mmap,
+ .vmap = drm_gem_dmabuf_vmap,
+ .vunmap = drm_gem_dmabuf_vunmap,
+};
+
+/**
+ * drm_gem_shmem_prime_export - implementation of the export callback
+ * @shmem: shmem GEM object
+ */
+struct dma_buf *drm_gem_shmem_prime_export(struct drm_gem_shmem_object *shmem,
+ int flags)
+{
+ struct drm_gem_object *obj = &shmem->base;
+ struct drm_device *dev = obj->dev;
+ struct dma_buf_export_info exp_info = {
+ .exp_name = KBUILD_MODNAME, /* white lie for debug */
+ .owner = dev->driver->fops->owner,
+ .ops = &drm_gem_shmem_prime_dmabuf_ops,
+ .size = obj->size,
+ .flags = flags,
+ .priv = obj,
+ .resv = obj->resv,
+ };
+
+ return drm_gem_dmabuf_export(dev, &exp_info);
+}
+
+/**
+ * drm_gem_shmem_prime_import - 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(struct drm_device *dev,
+ struct dma_buf *dma_buf)
+{
+ struct dma_buf_attachment *attach;
+ struct drm_gem_shmem_object *shmem;
+ size_t size;
+ int ret;
+
+ if (dma_buf->ops == &drm_gem_shmem_prime_dmabuf_ops) {
+ struct drm_gem_object *obj;
+
+ 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, 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);
+
MODULE_DESCRIPTION("DRM SHMEM memory-management helpers");
MODULE_IMPORT_NS("DMA_BUF");
MODULE_LICENSE("GPL v2");
diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h
index cef5a6b5a4d6..78ef91593a8e 100644
--- a/include/drm/drm_gem_shmem_helper.h
+++ b/include/drm/drm_gem_shmem_helper.h
@@ -110,6 +110,8 @@ int drm_gem_shmem_vmap(struct drm_gem_shmem_object *shmem,
void drm_gem_shmem_vunmap(struct drm_gem_shmem_object *shmem,
struct iosys_map *map);
int drm_gem_shmem_mmap(struct drm_gem_shmem_object *shmem, struct vm_area_struct *vma);
+struct dma_buf *drm_gem_shmem_prime_export(struct drm_gem_shmem_object *shmem,
+ int flags);
int drm_gem_shmem_pin_locked(struct drm_gem_shmem_object *shmem);
void drm_gem_shmem_unpin_locked(struct drm_gem_shmem_object *shmem);
@@ -168,6 +170,18 @@ static inline void drm_gem_shmem_object_print_info(struct drm_printer *p, unsign
drm_gem_shmem_print_info(shmem, p, indent);
}
+/**
+ * drm_gem_shmem_object_prime_export - GEM object function for export()
+ * @obj: GEM object
+ *
+ */
+static inline struct dma_buf *drm_gem_shmem_object_prime_export(struct drm_gem_object *obj,
+ int flags)
+{
+ struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
+
+ return drm_gem_shmem_prime_export(shmem, flags);
+}
/**
* drm_gem_shmem_object_pin - GEM object function for drm_gem_shmem_pin()
* @obj: GEM object
@@ -276,6 +290,8 @@ 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(struct drm_device *dev,
+ struct dma_buf *buf);
/**
* DRM_GEM_SHMEM_DRIVER_OPS - Default shmem GEM operations
@@ -287,4 +303,12 @@ 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
+/**
+ * This macro provides a shmem GEM operations that implementate a simple
+ * gem_prime_import.
+ */
+#define DRM_GEM_SHMEM_SIMPLE_DRIVER_OPS \
+ .gem_prime_import = drm_gem_shmem_prime_import, \
+ .dumb_create = drm_gem_shmem_dumb_create
+
#endif /* __DRM_GEM_SHMEM_HELPER_H__ */
--
2.17.1
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