Hi Bastien,

Le jeudi 10 avril 2025 à 16:53 +0200, Bastien Curutchet a écrit :

There is no way to transmit the DMA address of a buffer to userspace. Some UIO users need this to handle DMA from userspace.

To me this API is against all safe practice we've been pushing forward and has no place in DMA_BUF API.

If this is fine for the UIO subsystem to pass around physicial addresses, then make this part of the UIO device ioctl.

regards, Nicolas

Add a new dma_buf_ops operation that returns the DMA address. Add a new ioctl to transmit this DMA address to userspace.

Signed-off-by: Bastien Curutchet bastien.curutchet@bootlin.com

drivers/dma-buf/dma-buf.c    | 21 +++++++++++++++++++++  include/linux/dma-buf.h      |  1 +  include/uapi/linux/dma-buf.h |  1 +  3 files changed, 23 insertions(+)

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index 398418bd9731ad7a3a1f12eaea6a155fa77a22fe..cbbb518981e54e50f479c3d1fcf 6da6971f639c1 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -454,6 +454,24 @@ static long dma_buf_import_sync_file(struct dma_buf *dmabuf,  }  #endif   +static int dma_buf_get_dma_addr(struct dma_buf *dmabuf, u64 __user *arg) +{

• u64 addr;
• int ret;
• if (!dmabuf->ops->get_dma_addr)

• return -EINVAL;
  

• ret = dmabuf->ops->get_dma_addr(dmabuf, &addr);
• if (ret)

• return ret;
  

• if (copy_to_user(arg, &addr, sizeof(u64)))

• return -EFAULT;
  

• return 0;

+}

static long dma_buf_ioctl(struct file *file,     unsigned int cmd, unsigned long arg)  { @@ -504,6 +522,9 @@ static long dma_buf_ioctl(struct file *file,   return dma_buf_import_sync_file(dmabuf, (const void __user *)arg);  #endif

• case DMA_BUF_IOCTL_GET_DMA_ADDR:

• return dma_buf_get_dma_addr(dmabuf, (u64 __user
  

*)arg);

default:   return -ENOTTY;   } diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h index 36216d28d8bdc01a9c9c47e27c392413f7f6c5fb..ed4bf15d3ce82e7a86323fff459 699a9bc8baa3b 100644 --- a/include/linux/dma-buf.h +++ b/include/linux/dma-buf.h @@ -285,6 +285,7 @@ struct dma_buf_ops {     int (*vmap)(struct dma_buf *dmabuf, struct iosys_map *map);   void (*vunmap)(struct dma_buf *dmabuf, struct iosys_map *map);

• int (*get_dma_addr)(struct dma_buf *dmabuf, u64 *addr);

};    /** diff --git a/include/uapi/linux/dma-buf.h b/include/uapi/linux/dma- buf.h index 5a6fda66d9adf01438619e7e67fa69f0fec2d88d..f3aba46942042de6a2e3a4cca3e b3f87175e29c9 100644 --- a/include/uapi/linux/dma-buf.h +++ b/include/uapi/linux/dma-buf.h @@ -178,5 +178,6 @@ struct dma_buf_import_sync_file {  #define DMA_BUF_SET_NAME_B _IOW(DMA_BUF_BASE, 1, __u64)  #define DMA_BUF_IOCTL_EXPORT_SYNC_FILE _IOWR(DMA_BUF_BASE, 2, struct dma_buf_export_sync_file)  #define DMA_BUF_IOCTL_IMPORT_SYNC_FILE _IOW(DMA_BUF_BASE, 3, struct dma_buf_import_sync_file) +#define DMA_BUF_IOCTL_GET_DMA_ADDR _IOR(DMA_BUF_BASE, 4, __u64 *)    #endif