dma_fence's backend_ops functions ops->wait() and ops->release() are problematic because they prevent fence producers from unloading. Moreover, they can easily be implemented through simpler means more aligned with the dma_fence contract.
Since the declared goal of dma_fence is to move towards an implementation that supports driver-unload in all circumstances, we must prevent more parties from implementing those callbacks. Deprecate ops->release() and ops->wait() and document what users should do instead. Signed-off-by: Philipp Stanner <[email protected]> --- include/linux/dma-fence.h | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h index dd07d128adc3..59af0159cd25 100644 --- a/include/linux/dma-fence.h +++ b/include/linux/dma-fence.h @@ -220,6 +220,8 @@ struct dma_fence_ops { /** * @wait: * + * DEPRECATED! + * * Custom wait implementation, defaults to dma_fence_default_wait() if * not set. * @@ -236,6 +238,10 @@ struct dma_fence_ops { * Implementing this callback prevents the fence from detaching after * signaling and so it is necessary for the module providing the * dma_fence_ops to stay loaded as long as the dma_fence exists. + * + * Deprecated for the reason mentioned above. No new users must be + * implemented. Consumers of a fence can instead notify themselves by + * registering a callback on the fence. */ signed long (*wait)(struct dma_fence *fence, bool intr, signed long timeout); @@ -243,6 +249,8 @@ struct dma_fence_ops { /** * @release: * + * DEPRECATED! + * * Called on destruction of fence to release additional resources. * Can be called from irq context. This callback is optional. If it is * NULL, then dma_fence_free() is instead called as the default @@ -254,6 +262,12 @@ struct dma_fence_ops { * * If the callback is implemented the memory backing the dma_fence * object must be freed RCU safe. + * + * Deprecated because it prevents the producer of a fence from + * unloading. No new users must be implemented. Parties with a + * hypothetical need for this callback can instead simply and directly + * perform their custom release operations one RCU grace period after + * they have signaled the fence. */ void (*release)(struct dma_fence *fence); base-commit: 2302669bb4b52d581cc2589b90b3af7bb3783a28 -- 2.55.0
