[PATCH] udmabuf: add vmap method to udmabuf_ops

[Lukasz Wiecaszek]

The reason behind that patch is associated with videobuf2 subsystem
(or more genrally with v4l2 framework) and user created
dma buffers (udmabuf). In some circumstances
when dealing with V4L2_MEMORY_DMABUF buffers videobuf2 subsystem
wants to use dma_buf_vmap() method on the attached dma buffer.
As udmabuf does not have .vmap operation implemented,
such dma_buf_vmap() natually fails.

videobuf2_common: [cap-000000003473b2f1] __vb2_queue_alloc: allocated 3 buffers, 1 plane(s) each
videobuf2_common: [cap-000000003473b2f1] __prepare_dmabuf: buffer for plane 0 changed
videobuf2_common: [cap-000000003473b2f1] __prepare_dmabuf: failed to map dmabuf for plane 0
videobuf2_common: [cap-000000003473b2f1] __buf_prepare: buffer preparation failed: -14

The patch itself seems to be strighforward.
It adds implementation of .vmap method to 'struct dma_buf_ops udmabuf_ops'.
.vmap method itself uses vm_map_ram() to map pages linearly
into the kernel virtual address space (only if such mapping
hasn't been created yet).

Signed-off-by: Lukasz Wiecaszek <lukasz.wiecaszek at gmail.com>
---
 drivers/dma-buf/udmabuf.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
index 2bcdb935a3ac..8649fcbd05c4 100644
--- a/drivers/dma-buf/udmabuf.c
+++ b/drivers/dma-buf/udmabuf.c
@@ -12,6 +12,7 @@
 #include <linux/slab.h>
 #include <linux/udmabuf.h>
 #include <linux/hugetlb.h>
+#include <linux/vmalloc.h>
 
 static int list_limit = 1024;
 module_param(list_limit, int, 0644);
@@ -26,6 +27,7 @@ struct udmabuf {
 	struct page **pages;
 	struct sg_table *sg;
 	struct miscdevice *device;
+	void *vaddr;
 };
 
 static vm_fault_t udmabuf_vm_fault(struct vm_fault *vmf)
@@ -57,6 +59,21 @@ static int mmap_udmabuf(struct dma_buf *buf, struct vm_area_struct *vma)
 	return 0;
 }
 
+static int vmap_udmabuf(struct dma_buf *buf, struct dma_buf_map *map)
+{
+	struct udmabuf *ubuf = buf->priv;
+
+	if (!ubuf->vaddr) {
+		ubuf->vaddr = vm_map_ram(ubuf->pages, ubuf->pagecount, -1);
+		if (!ubuf->vaddr)
+			return -EINVAL;
+	}
+
+	dma_buf_map_set_vaddr(map, ubuf->vaddr);
+
+	return 0;
+}
+
 static struct sg_table *get_sg_table(struct device *dev, struct dma_buf *buf,
 				     enum dma_data_direction direction)
 {
@@ -159,6 +176,7 @@ static const struct dma_buf_ops udmabuf_ops = {
 	.unmap_dma_buf	   = unmap_udmabuf,
 	.release	   = release_udmabuf,
 	.mmap		   = mmap_udmabuf,
+	.vmap		   = vmap_udmabuf,
 	.begin_cpu_access  = begin_cpu_udmabuf,
 	.end_cpu_access    = end_cpu_udmabuf,
 };
-- 
2.25.1