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.
> > Robin. > >> Signed-off-by: Zhen Lei <thunder.leiz...@huawei.com> >> --- >> drivers/iommu/arm-smmu-v3.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c >> index 380969a..d2fbee3 100644 >> --- a/drivers/iommu/arm-smmu-v3.c >> +++ b/drivers/iommu/arm-smmu-v3.c >> @@ -728,7 +728,7 @@ static void queue_inc_prod(struct arm_smmu_queue *q) >> u32 prod = (Q_WRP(q, q->prod) | Q_IDX(q, q->prod)) + 1; >> >> q->prod = Q_OVF(q, q->prod) | Q_WRP(q, prod) | Q_IDX(q, prod); >> - writel(q->prod, q->prod_reg); >> + writel_relaxed(q->prod, q->prod_reg); >> } >> >> /* >> -- >> 2.5.0 >> >> > > > . > -- Thanks! BestRegards _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
