[Linaro-mm-sig] Re: [PATCH 4/4] dma-buf: drop caching of sg_tables

On 2/11/25 19:31, Christian König wrote:

That was purely for the transition from static to dynamic dma-buf handling and can be removed again now.

Signed-off-by: Christian König christian.koenig@amd.com

drivers/dma-buf/dma-buf.c | 34 -------------------------- drivers/dma-buf/udmabuf.c | 1 - drivers/gpu/drm/drm_prime.c | 1 - drivers/gpu/drm/virtio/virtgpu_prime.c | 1 - include/linux/dma-buf.h | 13 ---------- 5 files changed, 50 deletions(-)

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index 357b94a3dbaa..35221c4ddbf5 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -636,10 +636,6 @@ struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info) || !exp_info->ops->release)) return ERR_PTR(-EINVAL);

• if (WARN_ON(exp_info->ops->cache_sgt_mapping &&

•     (exp_info->ops->pin || exp_info->ops->unpin)))
  

• return ERR_PTR(-EINVAL);
  

• if (WARN_ON(!exp_info->ops->pin != !exp_info->ops->unpin)) return ERR_PTR(-EINVAL);

@@ -964,17 +960,7 @@ void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach) return; dma_resv_lock(dmabuf->resv, NULL);

• if (attach->sgt) {

• mangle_sg_table(attach->sgt);
  

• attach->dmabuf->ops->unmap_dma_buf(attach, attach->sgt,
  

• 				   attach->dir);
  

• if (dma_buf_pin_on_map(attach))
  

• 	dma_buf_unpin(attach);
  

• } list_del(&attach->node);
• dma_resv_unlock(dmabuf->resv);

if (dmabuf->ops->detach) @@ -1069,18 +1055,6 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach, dma_resv_assert_held(attach->dmabuf->resv);

• if (attach->sgt) {

• /*
  

•  * Two mappings with different directions for the same
  

•  * attachment are not allowed.
  

•  */
  

• if (attach->dir != direction &&
  

•     attach->dir != DMA_BIDIRECTIONAL)
  

• 	return ERR_PTR(-EBUSY);
  

• return attach->sgt;
  

• }
• if (dma_buf_pin_on_map(attach)) { ret = attach->dmabuf->ops->pin(attach); if (ret)

@@ -1105,11 +1079,6 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach, } mangle_sg_table(sg_table);

• if (attach->dmabuf->ops->cache_sgt_mapping) {

• attach->sgt = sg_table;
  

• attach->dir = direction;
  

• }

#ifdef CONFIG_DMA_API_DEBUG { struct scatterlist *sg; @@ -1190,9 +1159,6 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment *attach, dma_resv_assert_held(attach->dmabuf->resv);

• if (attach->sgt == sg_table)

• return;
  

• mangle_sg_table(sg_table); attach->dmabuf->ops->unmap_dma_buf(attach, sg_table, direction);

diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c index cc7398cc17d6..2fa2c9135eac 100644 --- a/drivers/dma-buf/udmabuf.c +++ b/drivers/dma-buf/udmabuf.c @@ -285,7 +285,6 @@ static int end_cpu_udmabuf(struct dma_buf *buf, } static const struct dma_buf_ops udmabuf_ops = {

• .cache_sgt_mapping = true, .map_dma_buf = map_udmabuf, .unmap_dma_buf = unmap_udmabuf, .release = release_udmabuf,

diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c index 32a8781cfd67..c284f306d597 100644 --- a/drivers/gpu/drm/drm_prime.c +++ b/drivers/gpu/drm/drm_prime.c @@ -810,7 +810,6 @@ int drm_gem_dmabuf_mmap(struct dma_buf *dma_buf, struct vm_area_struct *vma) EXPORT_SYMBOL(drm_gem_dmabuf_mmap); static const struct dma_buf_ops drm_gem_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,

diff --git a/drivers/gpu/drm/virtio/virtgpu_prime.c b/drivers/gpu/drm/virtio/virtgpu_prime.c index fe6a0b018571..c6f3be3cb914 100644 --- a/drivers/gpu/drm/virtio/virtgpu_prime.c +++ b/drivers/gpu/drm/virtio/virtgpu_prime.c @@ -75,7 +75,6 @@ static void virtgpu_gem_unmap_dma_buf(struct dma_buf_attachment *attach, static const struct virtio_dma_buf_ops virtgpu_dmabuf_ops = { .ops = {

• .cache_sgt_mapping = true,
  

  .attach = virtio_dma_buf_attach, .detach = drm_gem_map_detach, .map_dma_buf = virtgpu_gem_map_dma_buf,

diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h index c54ff2dda8cb..544f8f8c3f44 100644 --- a/include/linux/dma-buf.h +++ b/include/linux/dma-buf.h @@ -34,15 +34,6 @@ struct dma_buf_attachment;

• @vunmap: [optional] unmaps a vmap from the buffer

*/ struct dma_buf_ops {

• /**

•  * @cache_sgt_mapping:
  

•  *
  

•  * If true the framework will cache the first mapping made for each
  

•  * attachment. This avoids creating mappings for attachments multiple
  

•  * times.
  

•  */
  

• bool cache_sgt_mapping;
• /**
  • @attach:

@@ -493,8 +484,6 @@ struct dma_buf_attach_ops {

• @dmabuf: buffer for this attachment.
• @dev: device attached to the buffer.
• @node: list of dma_buf_attachment, protected by dma_resv lock of the dmabuf.

• • @sgt: cached mapping.
• • @dir: direction of cached mapping.
  • @peer2peer: true if the importer can handle peer resources without pages.
  • @priv: exporter specific attachment data.
  • @importer_ops: importer operations for this attachment, if provided

@@ -514,8 +503,6 @@ struct dma_buf_attachment { struct dma_buf *dmabuf; struct device *dev; struct list_head node;

• struct sg_table *sgt;
• enum dma_data_direction dir; bool peer2peer; const struct dma_buf_attach_ops *importer_ops; void *importer_priv;

Recalling being very confused by this cached sgt many years ago when faced it for the first time :)

Reviewed-by: Dmitry Osipenko dmitry.osipenko@collabora.com