linux-kernel - [PATCH 2/3] dma-buf: Add DMA_BUF_IOCTL_GET_DMA

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Message-Id: <20250410-uio-dma-v1-2-6468ace2c786@bootlin.com>
Date: Thu, 10 Apr 2025 16:53:19 +0200
From: Bastien Curutchet <bastien.curutchet@...tlin.com>
To: Sumit Semwal <sumit.semwal@...aro.org>, 
 Christian König <christian.koenig@....com>, 
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Thomas Petazzoni <thomas.petazzoni@...tlin.com>, 
 linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org, 
 linaro-mm-sig@...ts.linaro.org, linux-kernel@...r.kernel.org, 
 Bastien Curutchet <bastien.curutchet@...tlin.com>
Subject: [PATCH 2/3] dma-buf: Add DMA_BUF_IOCTL_GET_DMA_ADDR

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@...tlin.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