[Linaro-mm-sig] Re: [PATCH v5 1/6] dma-buf: Add dma_buf_{begin,end}_access()

Hi Christian,

Le lundi 22 janvier 2024 à 11:35 +0100, Christian König a écrit :

Am 19.01.24 um 15:13 schrieb Paul Cercueil:

...

These functions should be used by device drivers when they start and stop accessing the data of DMABUF. It allows DMABUF importers to cache the dma_buf_attachment while ensuring that the data they want to access is available for their device when the DMA transfers take place.

As Daniel already noted as well this is a complete no-go from the DMA-buf design point of view.

What do you mean "as Daniel already noted"? It was him who suggested this.

Regards, Christian.

Cheers, -Paul

...

Signed-off-by: Paul Cercueil paul@crapouillou.net

---

v5: New patch

drivers/dma-buf/dma-buf.c | 66 +++++++++++++++++++++++++++++++++++++++   include/linux/dma-buf.h   | 37 ++++++++++++++++++++++   2 files changed, 103 insertions(+)

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index 8fe5aa67b167..a8bab6c18fcd 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -830,6 +830,8 @@ static struct sg_table * __map_dma_buf(struct dma_buf_attachment *attach,    *     - dma_buf_mmap()    *     - dma_buf_begin_cpu_access()    *     - dma_buf_end_cpu_access()

• *     - dma_buf_begin_access()
• *     - dma_buf_end_access()

*     - dma_buf_map_attachment_unlocked()    *     - dma_buf_unmap_attachment_unlocked()    *     - dma_buf_vmap_unlocked() @@ -1602,6 +1604,70 @@ void dma_buf_vunmap_unlocked(struct dma_buf *dmabuf, struct iosys_map *map)   }   EXPORT_SYMBOL_NS_GPL(dma_buf_vunmap_unlocked, DMA_BUF);   +/**

• • @dma_buf_begin_access - Call before any hardware access from/to

the DMABUF

• • @attach: [in] attachment used for hardware access
• • @sg_table: [in] scatterlist used for the DMA transfer
• • @direction:  [in]    direction of DMA transfer
• */

+int dma_buf_begin_access(struct dma_buf_attachment *attach,

• 	 struct sg_table *sgt, enum
  

dma_data_direction dir) +{

• struct dma_buf *dmabuf;
• bool cookie;
• int ret;
• if (WARN_ON(!attach))

• return -EINVAL;
  

• dmabuf = attach->dmabuf;
• if (!dmabuf->ops->begin_access)

• return 0;
  

• cookie = dma_fence_begin_signalling();
• ret = dmabuf->ops->begin_access(attach, sgt, dir);
• dma_fence_end_signalling(cookie);
• if (WARN_ON_ONCE(ret))

• return ret;
  

• return 0;

+} +EXPORT_SYMBOL_NS_GPL(dma_buf_begin_access, DMA_BUF);

+/**

• • @dma_buf_end_access - Call after any hardware access from/to

the DMABUF

• • @attach: [in] attachment used for hardware access
• • @sg_table: [in] scatterlist used for the DMA transfer
• • @direction:  [in]    direction of DMA transfer
• */

+int dma_buf_end_access(struct dma_buf_attachment *attach,

•        struct sg_table *sgt, enum
  

dma_data_direction dir) +{

• struct dma_buf *dmabuf;
• bool cookie;
• int ret;
• if (WARN_ON(!attach))

• return -EINVAL;
  

• dmabuf = attach->dmabuf;
• if (!dmabuf->ops->end_access)

• return 0;
  

• cookie = dma_fence_begin_signalling();
• ret = dmabuf->ops->end_access(attach, sgt, dir);
• dma_fence_end_signalling(cookie);
• if (WARN_ON_ONCE(ret))

• return ret;
  

• return 0;

+} +EXPORT_SYMBOL_NS_GPL(dma_buf_end_access, DMA_BUF);

#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 8ff4add71f88..8ba612c7cc16 100644 --- a/include/linux/dma-buf.h +++ b/include/linux/dma-buf.h @@ -246,6 +246,38 @@ struct dma_buf_ops {    */    int (*end_cpu_access)(struct dma_buf *, enum dma_data_direction);

• /**

• * @begin_access:
  

• *
  

• * This is called from dma_buf_begin_access() when a
  

device driver

• * wants to access the data of the DMABUF. The exporter
  

can use this

• * to flush/sync the caches if needed.
  

• *
  

• * This callback is optional.
  

• *
  

• * Returns:
  

• *
  

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

• */
  

• int (*begin_access)(struct dma_buf_attachment *, struct

sg_table *,

• 	    enum dma_data_direction);
  

• /**

• * @end_access:
  

• *
  

• * This is called from dma_buf_end_access() when a device
  

driver is

• * done accessing the data of the DMABUF. The exporter can
  

use this

• * to flush/sync the caches if needed.
  

• *
  

• * This callback is optional.
  

• *
  

• * Returns:
  

• *
  

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

• */
  

• int (*end_access)(struct dma_buf_attachment *, struct

sg_table *,

• 	  enum dma_data_direction);
  

/**    * @mmap:    * @@ -606,6 +638,11 @@ void dma_buf_detach(struct dma_buf *dmabuf,   int dma_buf_pin(struct dma_buf_attachment *attach);   void dma_buf_unpin(struct dma_buf_attachment *attach);   +int dma_buf_begin_access(struct dma_buf_attachment *attach,

• 	 struct sg_table *sgt, enum
  

dma_data_direction dir); +int dma_buf_end_access(struct dma_buf_attachment *attach,

•        struct sg_table *sgt, enum
  

dma_data_direction dir);

struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info);     int dma_buf_fd(struct dma_buf *dmabuf, int flags);