[PATCH 2/3] drm/prime: Support importing DMA-BUF without sg_table
oushixiong
oushixiong1025 at 163.com
Wed Apr 30 14:13:48 UTC 2025
在 2025/4/30 19:03, Christian König 写道:
> On 4/30/25 10:56,oushixiong1025 at 163.com wrote:
>> From: Shixiong Ou<oushixiong at 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.
> This is unecessary. The extra abstraction in DRM is only useful when you want to implement the obj->funcs->get_sg_table() callback.
>
> When a driver doesn't want to expose an sg_table for a buffer or want some other special handling it can simply do so by implementing the DMA-buf interface directly.
>
> See drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c for an example on how to do this.
>
> Regards,
> Christian.
Thanks for the reminder,
most drivers that use DRM_GEM_SHADOW_PLANE_HELPER_FUNCSand
DRM_GEM_SHMEM_DRIVER_OPS
don't need to import the sg_table, such as the udl and the ast and so on
at the moment.
They just need to call dma_buf_vmap() to get the kernel virtual address
of the shared buffer.
So I wondered if there was a simple generic PRIME implementation for
these drivers.
If you don't recommend this, Maybe try to implement it in
DRM_GEM_SHMEM_DRIVER_OPS ?
Regards,
Shixiong Ou.
>> Signed-off-by: Shixiong Ou<oushixiong at 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__ */
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