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Diffstat (limited to 'Documentation/dma-buf-sharing.txt')
| -rw-r--r-- | Documentation/dma-buf-sharing.txt | 11 |
1 files changed, 6 insertions, 5 deletions
diff --git a/Documentation/dma-buf-sharing.txt b/Documentation/dma-buf-sharing.txt index 32ac32e773e1..ca44c5820585 100644 --- a/Documentation/dma-buf-sharing.txt +++ b/Documentation/dma-buf-sharing.txt @@ -352,7 +352,8 @@ Being able to mmap an export dma-buf buffer object has 2 main use-cases: 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. + used when the access happens. Note that DMA_BUF_IOCTL_SYNC can fail with + -EAGAIN or -EINTR, in which case it must be restarted. 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 @@ -366,10 +367,10 @@ Being able to mmap an export dma-buf buffer object has 2 main use-cases: 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. + For correctness and optimal performance, it is always required to use + SYNC_START and SYNC_END before and after, respectively, when accessing the + mapped address. Userspace cannot rely on coherent access, even when there + are systems where it just works without calling these ioctls. 2. Supporting existing mmap interfaces in importers |