Hi Am 16.09.20 um 14:59 schrieb Christian König: > Am 16.09.20 um 14:24 schrieb Daniel Vetter: >> On Wed, Sep 16, 2020 at 12:48:20PM +0200, Thomas Zimmermann wrote: >>> 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://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Fdri-devel%2F20200725191012.GA434957%40ravnborg.org%2F&data=02%7C01%7Cchristian.koenig%40amd.com%7C04e3cc3e03ae40f1fa0f08d85a3b6a68%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637358558524732385&sdata=wTmFuB95GhKUU%2F2Q91V0%2BtzAu4%2BEe3VBUcriBy3jx2g%3D&reserved=0 >>>>> >>>>> [2] >>>>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Fdri-devel%2F20200806085239.4606-1-tzimmermann%40suse.de%2F&data=02%7C01%7Cchristian.koenig%40amd.com%7C04e3cc3e03ae40f1fa0f08d85a3b6a68%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637358558524732385&sdata=L4rBHmegO63b%2FiTQdTyH158KNxAZwSuJCQOaFszo5L0%3D&reserved=0 >>>>> >>>> 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. >> If we make all the helpers static inline, then the compiler should be >> able >> to see that dma_buf_map.is_iomem is always the same, and produced really >> optimized code for it by pulling that check out from all the loops. >> >> So should only result in somewhat verbose code of having to call >> dma_buf_map pointer arthimetic helpers, but not in bad generated code. >> Still worth double-checking I think, since e.g. on x86 the generated code >> should be the same for both cases (but maybe the compiler doesn't see >> through the inline asm to realize that, so we might end up with 2 >> copies). > > Can we have that even independent of DMA-buf? We have essentially the > same problem in TTM and the code around that is a complete mess if you > ask me. I already put this into dma-buf because it's at the intersection of all the affected modules. For non-dma-buf pointers (say in framebuffer damage handling), the idea is to initialize struct dma_buf_map by hand and use this. Where would you want to put it? Best regards Thomas > > Christian. > >> -Daniel >> >> >>> 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 >>> >> >> >> > > _______________________________________________ > dri-devel mailing list > dri-devel@xxxxxxxxxxxxxxxxxxxxx > https://lists.freedesktop.org/mailman/listinfo/dri-devel -- 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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