[PATCH v6 1/4] uio: introduce UIO_MEM_DMA_COHERENT type

From: Chris Leech
Date: Mon Feb 05 2024 - 16:37:48 EST


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

This is mainly for the bnx2/bnx2x/bnx2i "cnic" interface, although there
are a few other uio drivers which map dma_alloc_coherent memory and will
be converted to use dma_mmap_coherent as well.

Signed-off-by: Nilesh Javali <njavali@xxxxxxxxxxx>
Signed-off-by: Chris Leech <cleech@xxxxxxxxxx>
---
v6: added kdoc comments

drivers/uio/uio.c | 47 ++++++++++++++++++++++++++++++++++++++
include/linux/uio_driver.h | 13 +++++++++++
2 files changed, 60 insertions(+)

diff --git a/drivers/uio/uio.c b/drivers/uio/uio.c
index 2d572f6c8ec83..bb77de6fa067e 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 +760,49 @@ 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;
+ struct uio_mem *mem;
+ void *addr;
+ int ret = 0;
+ int mi;
+
+ mi = uio_find_mem_index(vma);
+ if (mi < 0)
+ return -EINVAL;
+
+ mem = idev->info->mem + mi;
+
+ if (mem->addr & ~PAGE_MASK)
+ return -ENODEV;
+ if (mem->dma_addr & ~PAGE_MASK)
+ return -ENODEV;
+ if (!mem->dma_device)
+ return -ENODEV;
+ if (vma->vm_end - vma->vm_start > mem->size)
+ return -EINVAL;
+
+ dev_warn(mem->dma_device,
+ "use of UIO_MEM_DMA_COHERENT is highly discouraged");
+
+ /*
+ * 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;
+
+ addr = (void *)mem->addr;
+ ret = dma_mmap_coherent(mem->dma_device,
+ vma,
+ addr,
+ mem->dma_addr,
+ vma->vm_end - vma->vm_start);
+ vma->vm_pgoff = mi;
+
+ return ret;
+}
+
static int uio_mmap(struct file *filep, struct vm_area_struct *vma)
{
struct uio_listener *listener = filep->private_data;
@@ -806,6 +850,9 @@ 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 47c5962b876b0..18238dc8bfd35 100644
--- a/include/linux/uio_driver.h
+++ b/include/linux/uio_driver.h
@@ -28,19 +28,26 @@ struct uio_map;
* logical, virtual, or physical & phys_addr_t
* should always be large enough to handle any of
* the address types)
+ * @dma_addr: DMA handle set by dma_alloc_coherent, used with
+ * UIO_MEM_DMA_COHERENT only (@addr should be the
+ * void * returned from the same dma_alloc_coherent call)
* @offs: offset of device memory within the page
* @size: size of IO (multiple of page size)
* @memtype: type of memory addr points to
* @internal_addr: ioremap-ped version of addr, for driver internal use
+ * @dma_device: device struct that was passed to dma_alloc_coherent,
+ * used with UIO_MEM_DMA_COHERENT only
* @map: for use by the UIO core only.
*/
struct uio_mem {
const char *name;
phys_addr_t addr;
+ dma_addr_t dma_addr;
unsigned long offs;
resource_size_t size;
int memtype;
void __iomem *internal_addr;
+ struct device *dma_device;
struct uio_map *map;
};

@@ -158,6 +165,12 @@ extern int __must_check
#define UIO_MEM_LOGICAL 2
#define UIO_MEM_VIRTUAL 3
#define UIO_MEM_IOVA 4
+/*
+ * UIO_MEM_DMA_COHERENT exists for legacy drivers that had been getting by with
+ * improperly mapping DMA coherent allocations through the other modes.
+ * Do not use in new drivers.
+ */
+#define UIO_MEM_DMA_COHERENT 5

/* defines for uio_port->porttype */
#define UIO_PORT_NONE 0
--
2.43.0