Messages in this thread | | | Date | Mon, 14 Oct 2019 22:11:14 +0100 | From | Will Deacon <> | Subject | Re: [PATCH v2 3/4] iommu/mediatek: Use writel for TLB range invalidation |
| |
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.sun@mediatek.com> > > > Signed-off-by: Yong Wu <yong.wu@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.
> 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
| |