[PATCH 2/3] dma-buf: Add DMA_BUF_IOCTL_GET_DMA_ADDR

Bastien Curutchet
2025-04-10T14:53:23Z

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

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..cbbb518981e54e50f479c3d1fcf6da6971f639c1 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..ed4bf15d3ce82e7a86323fff459699a9bc8baa3b 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..f3aba46942042de6a2e3a4cca3eb3f87175e29c9 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

--
2.49.0