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. Will _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
