Adding Dmitry as well.
Am 11.11.22 um 12:45 schrieb 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).
Of hand that sounds sane to me.
You should probably mention somewhere in a code comment that the cached vaddr is protected by the reservation lock being taken. That's not necessary obvious to everybody.
Apart from that looks good to me.
Regards, Christian.
Signed-off-by: Lukasz Wiecaszek lukasz.wiecaszek@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, };