Dma-buf provides vmap() and vunmap() for retrieving 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. [1] https://lore.kernel.org/dri-devel/20200725191012.GA434957@xxxxxxxxxxxx/ [2] https://lore.kernel.org/dri-devel/20200806085239.4606-1-tzimmermann@xxxxxxx/ Thomas Zimmermann (3): 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 Documentation/driver-api/dma-buf.rst | 3 + drivers/dma-buf/dma-buf.c | 40 +++--- drivers/gpu/drm/drm_gem_cma_helper.c | 16 ++- drivers/gpu/drm/drm_gem_shmem_helper.c | 17 ++- drivers/gpu/drm/drm_prime.c | 14 +- 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 ++- 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 ++- include/drm/drm_prime.h | 5 +- include/linux/dma-buf-map.h | 126 ++++++++++++++++++ include/linux/dma-buf.h | 11 +- 15 files changed, 274 insertions(+), 82 deletions(-) create mode 100644 include/linux/dma-buf-map.h -- 2.28.0
