On 5/6/25 11:47, oushixiong1...@163.com wrote:
> From: Shixiong Ou <oushixi...@kylinos.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 <oushixi...@kylinos.cn>
> ---
> v1->v2:
> patch rebase.
>
> drivers/gpu/drm/drm_gem_shmem_helper.c | 95 ++++++++++++++++++++++++++
> include/drm/drm_gem_shmem_helper.h | 25 +++++++
> 2 files changed, 120 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c
> b/drivers/gpu/drm/drm_gem_shmem_helper.c
> index aa43265f4f4f..0c81a4f97684 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,
> @@ -800,6 +801,100 @@ 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 = {
> + .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,
> +};
Ok, I think I got it now.
You basically don't want to block providing the sg_table, but rather just avoid
that it is created al the time.
In that case duplicating the exporting side indeed doesn't make much sense.
> +
> +/**
> + * 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);
> +}
> +EXPORT_SYMBOL_GPL(drm_gem_shmem_prime_export);
And that here is then identical to drm_gem_prime_export().
> +
> +/**
> + * 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)
> +{
This is the only function which actually has some functional difference.
> + 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;
> + }
> + }
And you have the other two just to be able to check the dma_buf->ops in this
chunk here.
I suggest that you either expose drm_gem_prime_dmabuf_ops to
drm_gem_shmem_helper.c or make this chunk a separate function which is called
from drm_gem_shmem_prime_import().
And BTW you need a better name than drm_gem_shmem_prime_import(), something
which makes clear that only vmap is supported on the buffer.
Apart from that this seems to make sense to me now,
Christian.
> +
> + 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 b4f993da3cae..f2b4cc85b7f9 100644
> --- a/include/drm/drm_gem_shmem_helper.h
> +++ b/include/drm/drm_gem_shmem_helper.h
> @@ -121,6 +121,8 @@ int drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object
> *shmem,
> void drm_gem_shmem_vunmap_locked(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);
> @@ -179,6 +181,19 @@ 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
> @@ -287,6 +302,8 @@ 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
> @@ -298,4 +315,12 @@ 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__ */
