linux-kernel - Re: [PATCH v3 6/7] iommu/mediatek: Gather iova in iommu

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Date:   Mon, 18 Jan 2021 17:14:22 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Will Deacon <will@...nel.org>
Cc:     youlin.pei@...iatek.com, anan.sun@...iatek.com,
        Nicolas Boichat <drinkcat@...omium.org>,
        srv_heupstream@...iatek.com, chao.hao@...iatek.com,
        linux-kernel@...r.kernel.org,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Tomasz Figa <tfiga@...gle.com>,
        iommu@...ts.linux-foundation.org,
        linux-mediatek@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org,
        Matthias Brugger <matthias.bgg@...il.com>,
        Greg Kroah-Hartman <gregkh@...gle.com>, kernel-team@...roid.com
Subject: Re: [PATCH v3 6/7] iommu/mediatek: Gather iova in iommu_unmap to
 achieve tlb sync once

On 2021-01-18 16:58, Will Deacon wrote:
> On Mon, Jan 18, 2021 at 04:35:22PM +0000, Robin Murphy wrote:
>> On 2020-12-16 10:36, Yong Wu wrote:
>>> In current iommu_unmap, this code is:
>>>
>>> 	iommu_iotlb_gather_init(&iotlb_gather);
>>> 	ret = __iommu_unmap(domain, iova, size, &iotlb_gather);
>>> 	iommu_iotlb_sync(domain, &iotlb_gather);
>>>
>>> We could gather the whole iova range in __iommu_unmap, and then do tlb
>>> synchronization in the iommu_iotlb_sync.
>>>
>>> This patch implement this, Gather the range in mtk_iommu_unmap.
>>> then iommu_iotlb_sync call tlb synchronization for the gathered iova range.
>>> we don't call iommu_iotlb_gather_add_page since our tlb synchronization
>>> could be regardless of granule size.
>>>
>>> In this way, gather->start is impossible ULONG_MAX, remove the checking.
>>>
>>> This patch aims to do tlb synchronization *once* in the iommu_unmap.
>>
>> Assuming the update to patch #4 simply results in "unsigned long end = iova
>> + size - 1;" here,
>>
>> Reviewed-by: Robin Murphy <robin.murphy@....com>
> 
> There's a v4 here:
> 
> https://lore.kernel.org/r/20210107122909.16317-1-yong.wu@mediatek.com

Ha, so there is! Apparently I missed that in my post-holiday sweep last 
week and leant too heavily on the inbox-in-date-order assumption. Lemme 
just go catch up...

Thanks,
Robin.