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This patch is a stripped down version of the locking changes necessary to support dynamic DMA-buf handling. It adds a dynamic flag for both importers as well as exporters so that drivers can choose if they want the reservation object locked or unlocked during mapping of attachments. For compatibility between drivers we cache the DMA-buf mapping during attaching an importer as soon as exporter/importer disagree on the dynamic handling. Issues and solutions we considered: - We can't change all existing drivers, and existing improters have strong opinions about which locks they're holding while calling dma_buf_attachment_map/unmap. Exporters also have strong opinions about which locks they can acquire in their ->map/unmap callbacks, levaing no room for change. The solution to avoid this was to move the actual map/unmap out from this call, into the attach/detach callbacks, and cache the mapping. This works because drivers don't call attach/detach from deep within their code callchains (like deep in memory management code called from cs/execbuf ioctl), but directly from the fd2handle implementation. - The caching has some troubles on some soc drivers, which set other modes than DMA_BIDIRECTIONAL. We can't have 2 incompatible mappings, and we can't re-create the mapping at _map time due to the above locking fun. We very carefuly step around that by only caching at attach time if the dynamic mode between importer/expoert mismatches. - There's been quite some discussion on dma-buf mappings which need active cache management, which would all break down when caching, plus we don't have explicit flush operations on the attachment side. The solution to this was to shrug and keep the current discrepancy between what the dma-buf docs claim and what implementations do, with the hope that the begin/end_cpu_access hooks are good enough and that all necessary flushing to keep device mappings consistent will be done there. v2: cleanup set_name merge, improve kerneldoc v3: update commit message, kerneldoc and cleanup _debug_show() Signed-off-by: Christian König <christian.koenig@amd.com> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch> Link: https://patchwork.freedesktop.org/patch/336788/ |
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| clocksource | ||
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| dt-bindings | ||
| keys | ||
| kvm | ||
| linux | ||
| math-emu | ||
| media | ||
| misc | ||
| net | ||
| pcmcia | ||
| ras | ||
| rdma | ||
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| sound | ||
| target | ||
| trace | ||
| uapi | ||
| vdso | ||
| video | ||
| xen | ||
| Kbuild | ||