linux-kernel - [PATCH v3] udmabuf: add vmap and vunmap methods to udmabuf

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Date:   Tue, 15 Nov 2022 21:04:26 +0100
From:   Lukasz Wiecaszek <lukasz.wiecaszek@...glemail.com>
To:     Gerd Hoffmann <kraxel@...hat.com>
Cc:     Dmitry Osipenko <dmitry.osipenko@...labora.com>,
        Lukasz Wiecaszek <lukasz.wiecaszek@...il.com>,
        kernel test robot <lkp@...el.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Christian König <christian.koenig@....com>,
        dri-devel@...ts.freedesktop.org, linux-media@...r.kernel.org,
        linaro-mm-sig@...ts.linaro.org, linux-kernel@...r.kernel.org
Subject: [PATCH v3] udmabuf: add vmap and vunmap methods to udmabuf_ops

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@...il.com>
Reported-by: kernel test robot <lkp@...el.com>
---
v1: https://lore.kernel.org/linux-media/202211120352.G7WPASoP-lkp@intel.com/T/#t
v2: https://lore.kernel.org/linux-media/20221114052944.GA7264@thinkpad-p72/T/#t

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