lkml.org 
[lkml]   [2019]   [Oct]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH v2 3/4] iommu/mediatek: Use writel for TLB range invalidation
From
Date
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.

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".

>
> Will


\
 
 \ /
  Last update: 2019-10-12 08:24    [W:0.066 / U:14.856 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site