On Mon, 2019-10-14 at 22:11 +0100, Will Deacon wrote: > On Sat, Oct 12, 2019 at 02:23:47PM +0800, Yong Wu wrote: > > On Fri, 2019-10-11 at 17:29 +0100, Will Deacon wrote: > > > On Wed, Oct 09, 2019 at 09:19:02PM +0800, Yong Wu wrote: > > > > Use writel for the register F_MMU_INV_RANGE which is for triggering the > > > > HW work. We expect all the setting(iova_start/iova_end...) have already > > > > been finished before F_MMU_INV_RANGE. > > > > > > > > Signed-off-by: Anan.Sun <anan....@mediatek.com> > > > > Signed-off-by: Yong Wu <yong...@mediatek.com> > > > > --- > > > > This is a improvement rather than fixing a issue. > > > > --- > > > > drivers/iommu/mtk_iommu.c | 3 +-- > > > > 1 file changed, 1 insertion(+), 2 deletions(-) > > > > > > > > diff --git a/drivers/iommu/mtk_iommu.c b/drivers/iommu/mtk_iommu.c > > > > index 24a13a6..607f92c 100644 > > > > --- a/drivers/iommu/mtk_iommu.c > > > > +++ b/drivers/iommu/mtk_iommu.c > > > > @@ -187,8 +187,7 @@ static void mtk_iommu_tlb_add_flush(unsigned long > > > > iova, size_t size, > > > > writel_relaxed(iova, data->base + > > > > REG_MMU_INVLD_START_A); > > > > writel_relaxed(iova + size - 1, > > > > data->base + REG_MMU_INVLD_END_A); > > > > - writel_relaxed(F_MMU_INV_RANGE, > > > > - data->base + REG_MMU_INVALIDATE); > > > > + writel(F_MMU_INV_RANGE, data->base + > > > > REG_MMU_INVALIDATE); > > > > > > I don't understand this change. > > > > > > Why is it an "improvement" and which accesses are you ordering with the > > > writel? > > > > The register(F_MMU_INV_RANGE) will trigger HW to begin flush range. HW > > expect the other register iova_start/end/flush_type always is ready > > before trigger. thus I'd like use writel to guarantee the previous > > register has been finished. > > Given that these are all MMIO writes to the same device, then > writel_relaxed() should give you the ordering you need. If you look at > memory_barriers.txt, it says: > > | they [readX_relaxed() and writeX_relaxed()] are still guaranteed to > | be ordered with respect to other accesses from the same CPU thread > | to the same peripheral when operating on __iomem pointers mapped > | with the default I/O attributes.
Thanks for this info. See it now. then I will delete this patch in next version. > > > I didn't see the writel_relaxed cause some error in practice, we only > > think writel is necessary here in theory. so call it "improvement". > > Ok, but I don't think it's needed in this case. > > Will _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
