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Message-ID: <6b1469c6-b463-44fc-bd91-bff5c5622270@amd.com>
Date: Wed, 7 May 2025 14:59:31 +0200
From: Christian König <christian.koenig@....com>
To: oushixiong1025@....com
Cc: 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>,
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: Re: [PATCH v3 1/3] drm/shmem-helper: Import dmabuf without mapping
its sg_table
On 5/7/25 11:47, oushixiong1025@....com wrote:
> 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>
At least from my side that looks clean, so feel free to add Reviewed-by: Christian König <christian.koenig@....com>
But I would like to hear other opinions, e.g. Thomas as well. If nobody objects ping me to get this merged into drm-misc-next.
Regards,
Christian.
> ---
> v1->v2:
> Patch rebase.
> v2->v3:
> Rename the import callback function.
> Remove drm_gem_shmem_prime_export() and separate some codes
> to drm_gem_prime_import_self().
>
> drivers/gpu/drm/drm_gem_shmem_helper.c | 51 ++++++++++++++++++++++++++
> drivers/gpu/drm/drm_prime.c | 46 +++++++++++++++++------
> include/drm/drm_gem_shmem_helper.h | 15 ++++++++
> include/drm/drm_prime.h | 3 ++
> 4 files changed, 104 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
> index aa43265f4f4f..85900ec1954a 100644
> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
> @@ -800,6 +800,57 @@ drm_gem_shmem_prime_import_sg_table(struct drm_device *dev,
> }
> EXPORT_SYMBOL_GPL(drm_gem_shmem_prime_import_sg_table);
>
> +/**
> + * drm_gem_shmem_prime_import_no_sgt - 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_no_sgt(struct drm_device *dev,
> + struct dma_buf *dma_buf)
> +{
> + struct dma_buf_attachment *attach;
> + struct drm_gem_shmem_object *shmem;
> + struct drm_gem_object *obj;
> + size_t size;
> + int ret;
> +
> + obj = drm_gem_prime_import_self(dev, dma_buf);
> + if (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_no_sgt);
> +
> 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 d828502268b8..1e43b6022329 100644
> --- a/drivers/gpu/drm/drm_prime.c
> +++ b/drivers/gpu/drm/drm_prime.c
> @@ -910,6 +910,38 @@ struct dma_buf *drm_gem_prime_export(struct drm_gem_object *obj,
> }
> EXPORT_SYMBOL(drm_gem_prime_export);
>
> +
> +/**
> + * drm_gem_prime_import_self - Import a DMA-BUF exported from the same DRM device.
> + * @dev: drm_device to check against
> + * @dma_buf: dma-buf object to import
> + *
> + * This function checks if the DMA-BUF was exported from a GEM object belonging
> + * to @dev. If so, it increments the GEM object's refcount and returns it directly.
> + *
> + * Return: GEM object if it belongs to @dev, NULL otherwise.
> + */
> +struct drm_gem_object *drm_gem_prime_import_self(struct drm_device *dev,
> + struct dma_buf *dma_buf)
> +{
> + struct drm_gem_object *obj;
> +
> + 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;
> + }
> + }
> +
> + return NULL;
> +}
> +EXPORT_SYMBOL(drm_gem_prime_import_self);
> +
> /**
> * drm_gem_prime_import_dev - core implementation of the import callback
> * @dev: drm_device to import into
> @@ -933,17 +965,9 @@ struct drm_gem_object *drm_gem_prime_import_dev(struct drm_device *dev,
> 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;
> - }
> - }
> + obj = drm_gem_prime_import_self(dev, dma_buf);
> + if (obj)
> + return obj;
>
> if (!dev->driver->gem_prime_import_sg_table)
> return ERR_PTR(-EINVAL);
> diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h
> index b4f993da3cae..6e8e907bc43e 100644
> --- a/include/drm/drm_gem_shmem_helper.h
> +++ b/include/drm/drm_gem_shmem_helper.h
> @@ -287,6 +287,8 @@ 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_no_sgt(struct drm_device *dev,
> + struct dma_buf *buf);
>
> /**
> * DRM_GEM_SHMEM_DRIVER_OPS - Default shmem GEM operations
> @@ -298,4 +300,17 @@ 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
>
> +/**
> + * DRM_GEM_SHMEM_DRIVER_OPS_FOR_VMAP - shmem GEM operations
> + * without mapping sg_table on
> + * imported buffer.
> + *
> + * This macro provides a shortcut for setting the shmem GEM operations in
> + * the &drm_driver structure for drivers that do not require a sg_table on
> + * imported buffers. Only vmap is supported on imported buffer.
> + */
> +#define DRM_GEM_SHMEM_DRIVER_OPS_FOR_VMAP \
> + .gem_prime_import = drm_gem_shmem_prime_import_no_sgt, \
> + .dumb_create = drm_gem_shmem_dumb_create
> +
> #endif /* __DRM_GEM_SHMEM_HELPER_H__ */
> diff --git a/include/drm/drm_prime.h b/include/drm/drm_prime.h
> index fa085c44d4ca..b5179a9cde93 100644
> --- a/include/drm/drm_prime.h
> +++ b/include/drm/drm_prime.h
> @@ -100,6 +100,9 @@ struct dma_buf *drm_gem_prime_export(struct drm_gem_object *obj,
> unsigned long drm_prime_get_contiguous_size(struct sg_table *sgt);
>
> /* helper functions for importing */
> +struct drm_gem_object *drm_gem_prime_import_self(struct drm_device *dev,
> + struct dma_buf *dma_buf);
> +
> struct drm_gem_object *drm_gem_prime_import_dev(struct drm_device *dev,
> struct dma_buf *dma_buf,
> struct device *attach_dev);
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