linux-kernel - Re: [PATCH] iommu/mediatek: Move the tlb_sync into tlb

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Date:   Tue, 8 Oct 2019 16:18:32 +0800
From:   Yong Wu <yong.wu@...iatek.com>
To:     Will Deacon <will@...nel.org>
CC:     Matthias Brugger <matthias.bgg@...il.com>,
        Joerg Roedel <joro@...tes.org>,
        Will Deacon <will.deacon@....com>, <youlin.pei@...iatek.com>,
        <anan.sun@...iatek.com>, Nicolas Boichat <drinkcat@...omium.org>,
        <cui.zhang@...iatek.com>, <srv_heupstream@...iatek.com>,
        <chao.hao@...iatek.com>, <linux-kernel@...r.kernel.org>,
        Evan Green <evgreen@...omium.org>,
        "Tomasz Figa" <tfiga@...gle.com>,
        <iommu@...ts.linux-foundation.org>,
        <linux-mediatek@...ts.infradead.org>,
        Robin Murphy <robin.murphy@....com>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] iommu/mediatek: Move the tlb_sync into tlb_flush

On Mon, 2019-09-30 at 13:09 +0100, Will Deacon wrote:
> On Mon, Sep 30, 2019 at 01:42:22PM +0800, Yong Wu wrote:
> > The commit 4d689b619445 ("iommu/io-pgtable-arm-v7s: Convert to IOMMU API
> > TLB sync") help move the tlb_sync of unmap from v7s into the iommu
> > framework. It helps add a new function "mtk_iommu_iotlb_sync", But it
> > lacked the dom->pgtlock, then it will cause the variable
> > "tlb_flush_active" may be changed unexpectedly, we could see this warning
> > log randomly:
> > 
> > mtk-iommu 10205000.iommu: Partial TLB flush timed out, falling back to
> > full flush
> > 
> > To fix this issue, we can add dom->pgtlock in the "mtk_iommu_iotlb_sync".
> > And when checking this issue, we find that __arm_v7s_unmap call
> > io_pgtable_tlb_add_flush consecutively when it is supersection/largepage,
> > this also is potential unsafe for us. There is no tlb flush queue in the
> > MediaTek M4U HW. The HW always expect the tlb_flush/tlb_sync one by one.
> > If v7s don't always gurarantee the sequence, Thus, In this patch I move
> > the tlb_sync into tlb_flush(also rename the function deleting "_nosync").
> > and we don't care if it is leaf, rearrange the callback functions. Also,
> > the tlb flush/sync was already finished in v7s, then iotlb_sync and
> > iotlb_sync_all is unnecessary.
> > 
> > Besides, there are two minor changes:
> > a) 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.
> > b) Reduce the tlb timeout value from 100000us to 1000us. the original value
> > is so long that affect the multimedia performance.
> > 
> > Fixes: 4d689b619445 ("iommu/io-pgtable-arm-v7s: Convert to IOMMU API TLB sync")
> > Signed-off-by: Chao Hao <chao.hao@...iatek.com>
> > Signed-off-by: Yong Wu <yong.wu@...iatek.com>
> > ---
> > This patch looks break the logic for tlb_flush and tlb_sync. I'm not
> > sure if it
> > is reasonable. If someone has concern, I could change:
> > a) Add dom->pgtlock in the mtk_iommu_iotlb_sync
> > b) Add a io_pgtable_tlb_sync in [1].
> 
> The patch looks ok to me, but please could you split it up so that the
> timeout and writel are done separately?

Thanks for the quick review, I will separate them.

> 
> Thanks,
> 
> Will