Hi Thomas, On Fri, Sep 25, 2020 at 01:55:57PM +0200, Thomas Zimmermann wrote: > Dma-buf provides vmap() and vunmap() for retriving and releasing mappings > of dma-buf memory in kernel address space. The functions operate with plain > addresses and the assumption is that the memory can be accessed with load > and store operations. This is not the case on some architectures (e.g., > sparc64) where I/O memory can only be accessed with dedicated instructions. > > This patchset introduces struct dma_buf_map, which contains the address of > a buffer and a flag that tells whether system- or I/O-memory instructions > are required. > > Some background: updating the DRM framebuffer console on sparc64 makes the > kernel panic. This is because the framebuffer memory cannot be accessed with > system-memory instructions. We currently employ a workaround in DRM to > address this specific problem. [1] > > To resolve the problem, we'd like to address it at the most common point, > which is the dma-buf framework. The dma-buf mapping ideally knows if I/O > instructions are required and exports this information to it's users. The > new structure struct dma_buf_map stores the buffer address and a flag that > signals I/O memory. Affected users of the buffer (e.g., drivers, frameworks) > can then access the memory accordingly. > > This patchset only introduces struct dma_buf_map, and updates struct dma_buf > and it's interfaces. Further patches can update dma-buf users. For example, > there's a prototype patchset for DRM that fixes the framebuffer problem. [2] > > Further work: TTM, one of DRM's memory managers, already exports an > is_iomem flag of its own. It could later be switched over to exporting struct > dma_buf_map, thus simplifying some code. Several DRM drivers expect their > fbdev console to operate on I/O memory. These could possibly be switched over > to the generic fbdev emulation, as soon as the generic code uses struct > dma_buf_map. > > v3: > * update fastrpc driver (kernel test robot) > * expand documentation (Daniel) > * move documentation into separate patch > v2: > * always clear map parameter in dma_buf_vmap() (Daniel) > * include dma-buf-heaps and i915 selftests (kernel test robot) > * initialize cma_obj before using it in drm_gem_cma_free_object() > (kernel test robot) > > [1] https://lore.kernel.org/dri-devel/20200725191012.GA434957@xxxxxxxxxxxx/ > [2] https://lore.kernel.org/dri-devel/20200806085239.4606-1-tzimmermann@xxxxxxx/ > > Thomas Zimmermann (4): > dma-buf: Add struct dma-buf-map for storing struct dma_buf.vaddr_ptr > dma-buf: Use struct dma_buf_map in dma_buf_vmap() interfaces > dma-buf: Use struct dma_buf_map in dma_buf_vunmap() interfaces > dma-buf: Document struct dma_buf_map > > Documentation/driver-api/dma-buf.rst | 9 + > drivers/dma-buf/dma-buf.c | 42 ++-- > drivers/dma-buf/heaps/heap-helpers.c | 10 +- > drivers/gpu/drm/drm_gem_cma_helper.c | 20 +- > drivers/gpu/drm/drm_gem_shmem_helper.c | 17 +- > drivers/gpu/drm/drm_prime.c | 15 +- > drivers/gpu/drm/etnaviv/etnaviv_gem_prime.c | 13 +- > drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c | 13 +- > .../drm/i915/gem/selftests/i915_gem_dmabuf.c | 18 +- > .../gpu/drm/i915/gem/selftests/mock_dmabuf.c | 14 +- > drivers/gpu/drm/tegra/gem.c | 23 ++- > .../common/videobuf2/videobuf2-dma-contig.c | 17 +- > .../media/common/videobuf2/videobuf2-dma-sg.c | 19 +- > .../common/videobuf2/videobuf2-vmalloc.c | 21 +- > drivers/misc/fastrpc.c | 6 +- > include/drm/drm_prime.h | 5 +- > include/linux/dma-buf-map.h | 193 ++++++++++++++++++ > include/linux/dma-buf.h | 11 +- > 18 files changed, 372 insertions(+), 94 deletions(-) > create mode 100644 include/linux/dma-buf-map.h For drivers/media/common/videobuf2 changes: Acked-by: Tomasz Figa <tfiga@xxxxxxxxxxxx> Best regards, Tomasz
