Christian König
2025-May-08 09:54 UTC
[PATCH 4/4] drm/nouveau: Check dma_fence in canonical way
On 5/8/25 11:13, Philipp Stanner wrote:> On Mon, 2025-04-28 at 16:45 +0200, Christian K?nig 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 <phasta at 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); >> >