Subject: [PATCH 1/3] uio: introduce UIO_DMA_COHERENT type

From: Chris Leech <[email-masked]>
Date: Fri, 29 Sep 2023 10:00:21 -0700

Add a UIO memtype specificially for sharing dma_alloc_coherent
memory with userspace, backed by dma_mmap_coherent.

Signed-off-by: Chris Leech <[email-masked]>
---
 drivers/uio/uio.c          | 34 ++++++++++++++++++++++++++++++++++
 include/linux/uio_driver.h | 12 ++++++++++--
 2 files changed, 44 insertions(+), 2 deletions(-)

diff --git a/drivers/uio/uio.c b/drivers/uio/uio.c
index 62082d64ece0..f8f1f7ba6378 100644
--- a/drivers/uio/uio.c
+++ b/drivers/uio/uio.c
@@ -24,6 +24,7 @@
 #include <linux/kobject.h>
 #include <linux/cdev.h>
 #include <linux/uio_driver.h>
+#include <linux/dma-mapping.h>
 
 #define UIO_MAX_DEVICES		(1U << MINORBITS)
 
@@ -759,6 +760,36 @@ static int uio_mmap_physical(struct vm_area_struct *vma)
 			       vma->vm_page_prot);
 }
 
+static int uio_mmap_dma_coherent(struct vm_area_struct *vma)
+{
+	struct uio_device *idev = vma->vm_private_data;
+	int mi = uio_find_mem_index(vma);
+	struct uio_mem *mem;
+	int rc;
+
+	if (mi < 0)
+		return -EINVAL;
+	mem = idev->info->mem + mi;
+
+	if (mem->dma_addr & ~PAGE_MASK)
+		return -ENODEV;
+	if (vma->vm_end - vma->vm_start > mem->size)
+		return -EINVAL;
+
+	/*
+	 * UIO uses offset to index into the maps for a device.
+	 * We need to clear vm_pgoff for dma_mmap_coherent.
+	 */
+	vma->vm_pgoff = 0;
+	rc = dma_mmap_coherent(mem->dma_device,
+				vma,
+				mem->virtual_addr,
+				mem->dma_addr,
+				vma->vm_end - vma->vm_start);
+	vma->vm_pgoff = mi;
+	return rc;
+}
+
 static int uio_mmap(struct file *filep, struct vm_area_struct *vma)
 {
 	struct uio_listener *listener = filep->private_data;
@@ -806,6 +837,9 @@ static int uio_mmap(struct file *filep, struct vm_area_struct *vma)
 	case UIO_MEM_VIRTUAL:
 		ret = uio_mmap_logical(vma);
 		break;
+	case UIO_MEM_DMA_COHERENT:
+		ret = uio_mmap_dma_coherent(vma);
+		break;
 	default:
 		ret = -EINVAL;
 	}
diff --git a/include/linux/uio_driver.h b/include/linux/uio_driver.h
index 47c5962b876b..ede58e984658 100644
--- a/include/linux/uio_driver.h
+++ b/include/linux/uio_driver.h
@@ -36,11 +36,18 @@ struct uio_map;
  */
 struct uio_mem {
 	const char		*name;
-	phys_addr_t		addr;
+	union {
+		phys_addr_t	addr;
+		dma_addr_t	dma_addr;
+	};
 	unsigned long		offs;
 	resource_size_t		size;
 	int			memtype;
-	void __iomem		*internal_addr;
+	union {
+		void __iomem	*internal_addr;
+		void 		*virtual_addr;
+	};
+	struct device		*dma_device;
 	struct uio_map		*map;
 };
 
@@ -158,6 +165,7 @@ extern int __must_check
 #define UIO_MEM_LOGICAL	2
 #define UIO_MEM_VIRTUAL 3
 #define UIO_MEM_IOVA	4
+#define UIO_MEM_DMA_COHERENT	5
 
 /* defines for uio_port->porttype */
 #define UIO_PORT_NONE	0
-- 
2.41.0