diff options
author | Daniel Vetter <daniel.vetter@ffwll.ch> | 2016-02-11 20:04:51 -0200 |
---|---|---|
committer | Daniel Vetter <daniel.vetter@ffwll.ch> | 2016-02-12 16:01:32 +0100 |
commit | c11e391da2a8fe973c3c2398452000bed505851e (patch) | |
tree | b6d19ae34743c2765b7279614febadda5146b242 /Documentation | |
parent | e94cb37b34eb8a88fe847438dba55c3f18bf024a (diff) |
dma-buf: Add ioctls to allow userspace to flush
The userspace might need some sort of cache coherency management e.g. when CPU
and GPU domains are being accessed through dma-buf at the same time. To
circumvent this problem there are begin/end coherency markers, that forward
directly to existing dma-buf device drivers vfunc hooks. Userspace can make use
of those markers through the DMA_BUF_IOCTL_SYNC ioctl. The sequence would be
used like following:
- mmap dma-buf fd
- for each drawing/upload cycle in CPU 1. SYNC_START ioctl, 2. read/write
to mmap area 3. SYNC_END ioctl. This can be repeated as often as you
want (with the new data being consumed by the GPU or say scanout device)
- munmap once you don't need the buffer any more
v2 (Tiago): Fix header file type names (u64 -> __u64)
v3 (Tiago): Add documentation. Use enum dma_buf_sync_flags to the begin/end
dma-buf functions. Check for overflows in start/length.
v4 (Tiago): use 2d regions for sync.
v5 (Tiago): forget about 2d regions (v4); use _IOW in DMA_BUF_IOCTL_SYNC and
remove range information from struct dma_buf_sync.
v6 (Tiago): use __u64 structured padded flags instead enum. Adjust
documentation about the recommendation on using sync ioctls.
v7 (Tiago): Alex' nit on flags definition and being even more wording in the
doc about sync usage.
v9 (Tiago): remove useless is_dma_buf_file check. Fix sync.flags conditionals
and its mask order check. Add <linux/types.h> include in dma-buf.h.
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: David Herrmann <dh.herrmann@gmail.com>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Reviewed-by: Stéphane Marchesin <marcheu@chromium.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Signed-off-by: Tiago Vignatti <tiago.vignatti@intel.com>
Reviewed-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1455228291-29640-1-git-send-email-tiago.vignatti@intel.com
Diffstat (limited to 'Documentation')
-rw-r--r-- | Documentation/dma-buf-sharing.txt | 21 |
1 files changed, 20 insertions, 1 deletions
diff --git a/Documentation/dma-buf-sharing.txt b/Documentation/dma-buf-sharing.txt index 4f4a84b6903a..32ac32e773e1 100644 --- a/Documentation/dma-buf-sharing.txt +++ b/Documentation/dma-buf-sharing.txt @@ -350,7 +350,26 @@ Being able to mmap an export dma-buf buffer object has 2 main use-cases: handles, too). So it's beneficial to support this in a similar fashion on dma-buf to have a good transition path for existing Android userspace. - No special interfaces, userspace simply calls mmap on the dma-buf fd. + No special interfaces, userspace simply calls mmap on the dma-buf fd, making + sure that the cache synchronization ioctl (DMA_BUF_IOCTL_SYNC) is *always* + used when the access happens. This is discussed next paragraphs. + + Some systems might need some sort of cache coherency management e.g. when + CPU and GPU domains are being accessed through dma-buf at the same time. To + circumvent this problem there are begin/end coherency markers, that forward + directly to existing dma-buf device drivers vfunc hooks. Userspace can make + use of those markers through the DMA_BUF_IOCTL_SYNC ioctl. The sequence + would be used like following: + - mmap dma-buf fd + - for each drawing/upload cycle in CPU 1. SYNC_START ioctl, 2. read/write + to mmap area 3. SYNC_END ioctl. This can be repeated as often as you + want (with the new data being consumed by the GPU or say scanout device) + - munmap once you don't need the buffer any more + + Therefore, for correctness and optimal performance, systems with the memory + cache shared by the GPU and CPU i.e. the "coherent" and also the + "incoherent" are always required to use SYNC_START and SYNC_END before and + after, respectively, when accessing the mapped address. 2. Supporting existing mmap interfaces in importers |