On 11/11/22 15:05, Christian König wrote: > 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. Adding a comment won't hurt. We have the dma_resv_assert_held() in dma_buf_vmap() that will help spotting a missing lock at runtime by developers. While the dmbuf_ops->vmap() shouldn't be ever used directly by importers. -- Best regards, Dmitry
