Hi Am 16.09.20 um 11:37 schrieb Daniel Vetter: > 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. Yup, it would be nice if TTM could had out these types automatically. Then all TTM-based drivers would automatically support it. > > 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. We have some framebuffer helpers that rely on pointer arithmetic, so we'd need that too. No big deal wrt code, but I was worried about the overhead. If a loop goes over framebuffer memory, there's an if/else branch for each access to the memory buffer. Best regards Thomas > -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 >> > -- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Maxfeldstr. 5, 90409 Nürnberg, Germany (HRB 36809, AG Nürnberg) Geschäftsführer: Felix Imendörffer
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