On Thu, May 22, 2025 at 02:34:33PM +0200, Christian König wrote: > See all the functions inside include/linux/dma-fence.h can be used by > everybody. It's basically the public interface of the dma_fence object.
As you write below, in certain cases it is valid to call this from drivers, so it's not unreasonable to have it as part of the public API. > So testing if a fence is signaled without calling the callback is only > allowed by whoever implemented the fence. > > In other words nouveau can test nouveau fences, i915 can test i915 fences, > amdgpu can test amdgpu fences etc... But if you have the wrapper that makes > it officially allowed that nouveau starts testing i915 fences and that would > be problematic. In general, I like the __dma_fence_is_signaled() helper, because this way we can document in which cases it is allowed to be used, i.e. the ones you descibe above. test_bit() can be called by anyone and there is no documentation comment explaining that it is only allowed under certain conditions. Having the __dma_fence_is_signaled() helper properly documented could get you rid of having to explain in which case the test_bit() dance is allowed to do over and over again. :-) I also think the name is good, since the '__' prefix already implies that there are some restrictions on the use of this helper.
