On 2017/6/21 17:08, Will Deacon wrote: > On Wed, Jun 21, 2017 at 09:28:23AM +0800, Leizhen (ThunderTown) wrote: >> On 2017/6/20 19:35, Robin Murphy wrote: >>> On 20/06/17 12:04, Zhen Lei wrote: >>>> This function is protected by spinlock, and the latter will do memory >>>> barrier implicitly. So that we can safely use writel_relaxed. In fact, the >>>> dmb operation will lengthen the time protected by lock, which indirectly >>>> increase the locking confliction in the stress scene. >>> >>> If you remove the DSB between writing the commands (to Normal memory) >>> and writing the pointer (to Device memory), how can you guarantee that >>> the complete command is visible to the SMMU and it isn't going to try to >>> consume stale memory contents? The spinlock is irrelevant since it's >>> taken *before* the command is written. >> OK, I see, thanks. Let's me see if there are any other methods. And I think >> that this may should be done well by hardware. > > FWIW, I did use the _relaxed variants wherever I could when I wrote the > driver. There might, of course, be bugs, but it's not like the normal case > for drivers where the author didn't consider the _relaxed accessors > initially. A good news. I got a new idea and I will post v2 later.
> > Will > > . > -- Thanks! BestRegards _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
