On 5/8/25 11:13, Philipp Stanner wrote: > On Mon, 2025-04-28 at 16:45 +0200, Christian König wrote: >> On 4/24/25 15:02, Philipp Stanner wrote: >>> In nouveau_fence_done(), a fence is checked for being signaled by >>> manually evaluating the base fence's bits. This can be done in a >>> canonical manner through dma_fence_is_signaled(). >>> >>> Replace the bit-check with dma_fence_is_signaled(). >>> >>> Signed-off-by: Philipp Stanner <pha...@kernel.org> >> >> >> I think the bit check was used here as fast path optimization because >> we later call dma_fence_is_signaled() anyway. > > That fast path optimization effectively saves one JMP instruction to > the function.
What I meant was that we might completely drop that optimization. It looks like overkill and potentially hides bugs. Regards, Christian. > > I'm increasingly of the opinion that we shall work towards all DRM > users only ever using infrastructure through officially documented API > functions, without touching internal data structures. > >> Feel free to add my acked-by, but honestly what nouveau does here >> looks rather suspicious to me. > > :) > > > P. > >> >> Regards, >> Christian. >> >>> --- >>> drivers/gpu/drm/nouveau/nouveau_fence.c | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/drivers/gpu/drm/nouveau/nouveau_fence.c >>> b/drivers/gpu/drm/nouveau/nouveau_fence.c >>> index fb9811938c82..d5654e26d5bc 100644 >>> --- a/drivers/gpu/drm/nouveau/nouveau_fence.c >>> +++ b/drivers/gpu/drm/nouveau/nouveau_fence.c >>> @@ -253,7 +253,7 @@ nouveau_fence_done(struct nouveau_fence *fence) >>> struct nouveau_channel *chan; >>> unsigned long flags; >>> >>> - if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence- >>>> base.flags)) >>> + if (dma_fence_is_signaled(&fence->base)) >>> return true; >>> >>> spin_lock_irqsave(&fctx->lock, flags); >> >
