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

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Date:   Mon, 30 Sep 2019 13:09:27 +0100
From:   Will Deacon <will@...nel.org>
To:     Yong Wu <yong.wu@...iatek.com>
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, 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,

Will