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Message-Id: <20250430085658.540746-2-oushixiong1025@163.com>
Date: Wed, 30 Apr 2025 16:56:57 +0800
From: oushixiong1025@....com
To: Sumit Semwal <sumit.semwal@...aro.org>
Cc: Christian König <christian.koenig@....com>,
	linux-media@...r.kernel.org,
	dri-devel@...ts.freedesktop.org,
	linaro-mm-sig@...ts.linaro.org,
	linux-kernel@...r.kernel.org,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	David Airlie <airlied@...il.com>,
	Simona Vetter <simona@...ll.ch>,
	Dave Airlie <airlied@...hat.com>,
	Sean Paul <sean@...rly.run>,
	Shixiong Ou <oushixiong@...inos.cn>
Subject: [PATCH 2/3] drm/prime: Support importing DMA-BUF without sg_table

From: Shixiong Ou <oushixiong@...inos.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@...inos.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


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