-----Original Message----- From: dri-devel dri-devel-bounces@lists.freedesktop.org On Behalf Of Thomas Zimmermann Sent: Friday, January 8, 2021 4:43 AM To: sumit.semwal@linaro.org; christian.koenig@amd.com; airlied@redhat.com; daniel@ffwll.ch; maarten.lankhorst@linux.intel.com; mripard@kernel.org; kraxel@redhat.com; hdegoede@redhat.com; sean@poorly.run; eric@anholt.net; sam@ravnborg.org Cc: Daniel Vetter daniel.vetter@ffwll.ch; dri-devel@lists.freedesktop.org; virtualization@lists.linux-foundation.org; linaro-mm-sig@lists.linaro.org; Thomas Zimmermann tzimmermann@suse.de; linux- media@vger.kernel.org Subject: [PATCH v4 01/13] dma-buf: Add vmap_local and vnumap_local operations

The existing dma-buf calls dma_buf_vmap() and dma_buf_vunmap() are allowed to pin the buffer or acquire the buffer's reservation object lock.

This is a problem for callers that only require a short-term mapping of the buffer without the pinning, or callers that have special locking requirements. These may suffer from unnecessary overhead or interfere with regular pin operations.

The new interfaces dma_buf_vmap_local(), dma_buf_vunmapo_local(), and their rsp callbacks in struct dma_buf_ops provide an alternative without pinning or reservation locking. Callers are responsible for these operations.

v4:

• update documentation (Daniel)

Signed-off-by: Thomas Zimmermann tzimmermann@suse.de Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch Suggested-by: Daniel Vetter daniel.vetter@ffwll.ch

---

drivers/dma-buf/dma-buf.c | 81 +++++++++++++++++++++++++++++++++++++++ include/linux/dma-buf.h | 34 ++++++++++++++++ 2 files changed, 115 insertions(+)

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index b8465243eca2..01f9c74d97fa 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -1295,6 +1295,87 @@ void dma_buf_vunmap(struct dma_buf *dmabuf, struct dma_buf_map *map) } EXPORT_SYMBOL_GPL(dma_buf_vunmap);

+/**

• • dma_buf_vmap_local - Create virtual mapping for the buffer object into

kernel

• • address space.
• • @dmabuf: [in] buffer to vmap
• • @map: [out] returns the vmap pointer
• • Unlike dma_buf_vmap() this is a short term mapping and will not pin
• • the buffer. The struct dma_resv for the @dmabuf must be locked until
• • dma_buf_vunmap_local() is called.
• • Returns:
• • 0 on success, or a negative errno code otherwise.
• */

+int dma_buf_vmap_local(struct dma_buf *dmabuf, struct dma_buf_map *map) +{

• struct dma_buf_map ptr;
• int ret = 0;
• dma_buf_map_clear(map);
• if (WARN_ON(!dmabuf))

• return -EINVAL;
  

• dma_resv_assert_held(dmabuf->resv);
• if (!dmabuf->ops->vmap_local)

• return -EINVAL;
  

You are clearing the map, and then doing the above checks.

Is it ok to change the map info and then exit on error?

Mike

• mutex_lock(&dmabuf->lock);
• if (dmabuf->vmapping_counter) {

• dmabuf->vmapping_counter++;
  

• BUG_ON(dma_buf_map_is_null(&dmabuf->vmap_ptr));
  

• *map = dmabuf->vmap_ptr;
  

• goto out_unlock;
  

• }
• BUG_ON(dma_buf_map_is_set(&dmabuf->vmap_ptr));
• ret = dmabuf->ops->vmap_local(dmabuf, &ptr);
• if (WARN_ON_ONCE(ret))

• goto out_unlock;
  

• dmabuf->vmap_ptr = ptr;
• dmabuf->vmapping_counter = 1;
• *map = dmabuf->vmap_ptr;

+out_unlock:

• mutex_unlock(&dmabuf->lock);
• return ret;

+} +EXPORT_SYMBOL_GPL(dma_buf_vmap_local);

+/**

• • dma_buf_vunmap_local - Unmap a vmap obtained by

dma_buf_vmap_local.

• • @dmabuf: [in] buffer to vunmap
• • @map: [in] vmap pointer to vunmap
• • Release a mapping established with dma_buf_vmap_local().
• */

+void dma_buf_vunmap_local(struct dma_buf *dmabuf, struct dma_buf_map *map) +{

• if (WARN_ON(!dmabuf))

• return;
  

• dma_resv_assert_held(dmabuf->resv);
• BUG_ON(dma_buf_map_is_null(&dmabuf->vmap_ptr));
• BUG_ON(dmabuf->vmapping_counter == 0);
• BUG_ON(!dma_buf_map_is_equal(&dmabuf->vmap_ptr, map));
• mutex_lock(&dmabuf->lock);
• if (--dmabuf->vmapping_counter == 0) {

• if (dmabuf->ops->vunmap_local)
  

• 	dmabuf->ops->vunmap_local(dmabuf, map);
  

• dma_buf_map_clear(&dmabuf->vmap_ptr);
  

• }
• mutex_unlock(&dmabuf->lock);

+} +EXPORT_SYMBOL_GPL(dma_buf_vunmap_local);

#ifdef CONFIG_DEBUG_FS static int dma_buf_debug_show(struct seq_file *s, void *unused) { diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h index 628681bf6c99..aeed754b5467 100644 --- a/include/linux/dma-buf.h +++ b/include/linux/dma-buf.h @@ -264,6 +264,38 @@ struct dma_buf_ops {

int (*vmap)(struct dma_buf *dmabuf, struct dma_buf_map *map); void (*vunmap)(struct dma_buf *dmabuf, struct dma_buf_map *map);

• /**

• * @vmap_local:
  

• *
  

• * Creates a virtual mapping for the buffer into kernel address space.
  

• *
  

• * This callback establishes short-term mappings for situations where
  

• * callers only use the buffer for a bounded amount of time; such as
  

• * updates to the framebuffer or reading back contained information.
  

• * In contrast to the regular @vmap callback, vmap_local does never
  

pin

• * the buffer to a specific domain or acquire the buffer's reservation
  

• * lock.
  

• *
  

• * This is called with the &dma_buf.resv object locked. Callers must
  

hold

• * the lock until after removing the mapping with @vunmap_local.
  

• *
  

• * This callback is optional.
  

• *
  

• * Returns:
  

• *
  

• * 0 on success or a negative error code on failure.
  

• */
  

• int (*vmap_local)(struct dma_buf *dmabuf, struct dma_buf_map

*map);

• /**

• * @vunmap_local:
  

• *
  

• * Removes a virtual mapping that was established by @vmap_local.
  

• *
  

• * This callback is optional.
  

• */
  

• void (*vunmap_local)(struct dma_buf *dmabuf, struct dma_buf_map

*map); };

/** @@ -501,4 +533,6 @@ int dma_buf_mmap(struct dma_buf *, struct vm_area_struct *, unsigned long); int dma_buf_vmap(struct dma_buf *dmabuf, struct dma_buf_map *map); void dma_buf_vunmap(struct dma_buf *dmabuf, struct dma_buf_map *map); +int dma_buf_vmap_local(struct dma_buf *dmabuf, struct dma_buf_map *map); +void dma_buf_vunmap_local(struct dma_buf *dmabuf, struct dma_buf_map *map);

#endif /* __DMA_BUF_H__ */

2.29.2

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