Trying to explain a bit how this thing works. In my opinion diagrams are a bit easier to understand than words. Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@xxxxxxxxx> --- drivers/dma-buf/dma-fence-chain.c | 37 +++++++++++++++++++++++++++++++ 1 file changed, 37 insertions(+) diff --git a/drivers/dma-buf/dma-fence-chain.c b/drivers/dma-buf/dma-fence-chain.c index 3d123502ff12..ac90ddf37b55 100644 --- a/drivers/dma-buf/dma-fence-chain.c +++ b/drivers/dma-buf/dma-fence-chain.c @@ -9,6 +9,43 @@ #include <linux/dma-fence-chain.h> +/** + * DOC: DMA fence chains overview + * + * DMA fence chains, represented by &struct dma_fence_chain, are a kernel + * internal synchronization primitive providing a wrapping mechanism of other + * DMA fences in the form a single link list. + * + * One of the use case of this primitive is to implement Vulkan timeline + * semaphores (see VK_KHR_timeline_semaphore extension or Vulkan specification + * 1.2). + * + * Each DMA fence chain item wraps 2 items : + * + * - A previous DMA fence. + * + * - A DMA fence associated to the current &struct dma_fence_chain. + * + * A DMA fence chain becomes signaled when its previous fence as well as its + * associated fence are signaled. If a chain of dma fence chains is created, + * this property recurses, meaning that any dma fence chain element in the + * list becomes signaled only if its associated fence and all the previous + * fences in the chain are also signaled. + * + * A DMA fence chain's seqno is specified through dma_fence_chain_init(). This + * value is lower bound to the seqno of the previous fence to ensure the chain + * is monotically increasing. + * + * By traversing the chain's linked list, one can compute a seqno number + * associated with the chain such that is the highest number for which all + * previous fences have signaled. + * + * One can also traverse the chain's linked list to find a &struct + * dma_fence_chain that when signaled guarantees that all previous fences in + * the chain are signaled. dma_fence_chain_find_seqno() provides this + * functionality. + */ + static bool dma_fence_chain_enable_signaling(struct dma_fence *fence); /** -- 2.27.0 _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
