On Mon, Sep 14, 2020 at 01:25:18PM +0200, Thomas Zimmermann wrote: > 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/ lgtm, imo ready to convert the follow-up patches over to this. But I think would be good to get at least some ack from the ttm side for the overall plan. Also, I think we should put all the various helpers (writel/readl, memset, memcpy, whatever else) into the dma-buf-map.h helper, so that most code using this can just treat it as an abstract pointer type and never look underneath it. -Daniel > > 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 > -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
