On Wed, Nov 16, 2022 at 01:01:46PM +0100, Christian König wrote: > Am 15.11.22 um 21:04 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: __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> > > > Reported-by: kernel test robot <lkp@xxxxxxxxx> > > Please drop this line, the kernel test robot should only be mentioned if the > original report came from it. > > And keep in mind that it might be necessary to implement begin/end cpu > access callbacks as well. > > Apart from that the patch is Acked-by: Christian König > <christian.koenig@xxxxxxx>. > > Regards, > Christian. Thanks for that lesson with the 'kernel test robot' line. The second issue with begin/end cpu access callbacks is more complicated to me. My understaning is that memory allocated for udambuf will be the memory obtained most likely (if not always) by memfd_create(). So this will be the anonymous system memory which is 'by definition' coherent for cpu access. So no need for begin/end callbacks. But if I miss something, plese let me/us know. > > > --- > > 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 > > > > 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, > > }; >
