uio: introduce UIO_MEM_DMA_COHERENT type

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 <[e-mail]>
Signed-off-by: Chris Leech <[e-mail]>
Reviewed-by: Christoph Hellwig <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/uio/uio.c

···
 #include <linux/kobject.h>
 #include <linux/cdev.h>
 #include <linux/uio_driver.h>
+#include <linux/dma-mapping.h>
 
 #define UIO_MAX_DEVICES		(1U << MINORBITS)
 
···
 			       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;
···
 	case UIO_MEM_LOGICAL:
 	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;

include/linux/uio_driver.h

···
  *			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;
 };
 
···
 #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