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@xxxxxxxxx>
---
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
