[PATCH v4] udmabuf: add vmap and vunmap methods to udmabuf_ops

From: Lukasz Wiecaszek
Date: Thu Nov 17 2022 - 00:00:18 EST


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

The patch itself seems to be strighforward.
It adds implementation of .vmap and .vunmap methods
to 'struct dma_buf_ops udmabuf_ops'.
.vmap method itself uses vm_map_ram() to map pages linearly
into the kernel virtual address space.
.vunmap removes mapping created earlier by .vmap.
All locking and 'vmapping counting' is done in dma_buf.c
so it seems to be redundant/unnecessary in .vmap/.vunmap.

Signed-off-by: Lukasz Wiecaszek <lukasz.wiecaszek@xxxxxxxxx>
---
v1: https://lore.kernel.org/linux-media/202211120352.G7WPASoP-lkp@xxxxxxxxx/T/#t
v2: https://lore.kernel.org/linux-media/20221114052944.GA7264@thinkpad-p72/T/#t
v3: https://lore.kernel.org/linux-media/4f92e95f-a0dc-4eac-4c08-0df85de78ae7@xxxxxxxxxxxxx/T/#t

v3 -> v4: Removed line/info 'reported by kernel test robot'
v2 -> v3: Added .vunmap to 'struct dma_buf_ops udmabuf_ops'
v1 -> v2: Patch prepared and tested against 6.1.0-rc2+

drivers/dma-buf/udmabuf.c | 28 ++++++++++++++++++++++++++++
1 file changed, 28 insertions(+)

diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
index 283816fbd72f..740d6e426ee9 100644
--- a/drivers/dma-buf/udmabuf.c
+++ b/drivers/dma-buf/udmabuf.c
@@ -13,6 +13,8 @@
#include <linux/slab.h>
#include <linux/udmabuf.h>
#include <linux/hugetlb.h>
+#include <linux/vmalloc.h>
+#include <linux/iosys-map.h>

static int list_limit = 1024;
module_param(list_limit, int, 0644);
@@ -60,6 +62,30 @@ static int mmap_udmabuf(struct dma_buf *buf, struct vm_area_struct *vma)
return 0;
}

+static int vmap_udmabuf(struct dma_buf *buf, struct iosys_map *map)
+{
+ struct udmabuf *ubuf = buf->priv;
+ void *vaddr;
+
+ dma_resv_assert_held(buf->resv);
+
+ vaddr = vm_map_ram(ubuf->pages, ubuf->pagecount, -1);
+ if (!vaddr)
+ return -EINVAL;
+
+ iosys_map_set_vaddr(map, vaddr);
+ return 0;
+}
+
+static void vunmap_udmabuf(struct dma_buf *buf, struct iosys_map *map)
+{
+ struct udmabuf *ubuf = buf->priv;
+
+ dma_resv_assert_held(buf->resv);
+
+ vm_unmap_ram(map->vaddr, ubuf->pagecount);
+}
+
static struct sg_table *get_sg_table(struct device *dev, struct dma_buf *buf,
enum dma_data_direction direction)
{
@@ -162,6 +188,8 @@ static const struct dma_buf_ops udmabuf_ops = {
.unmap_dma_buf = unmap_udmabuf,
.release = release_udmabuf,
.mmap = mmap_udmabuf,
+ .vmap = vmap_udmabuf,
+ .vunmap = vunmap_udmabuf,
.begin_cpu_access = begin_cpu_udmabuf,
.end_cpu_access = end_cpu_udmabuf,
};
--
2.25.1