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

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Date:   Mon, 18 Jan 2021 16:35:22 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Yong Wu <yong.wu@...iatek.com>, Joerg Roedel <joro@...tes.org>,
        Will Deacon <will@...nel.org>
Cc:     Matthias Brugger <matthias.bgg@...il.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Tomasz Figa <tfiga@...gle.com>,
        linux-mediatek@...ts.infradead.org, srv_heupstream@...iatek.com,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        iommu@...ts.linux-foundation.org, youlin.pei@...iatek.com,
        Nicolas Boichat <drinkcat@...omium.org>, anan.sun@...iatek.com,
        chao.hao@...iatek.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 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>

> Signed-off-by: Yong Wu <yong.wu@...iatek.com>
> ---
>   drivers/iommu/mtk_iommu.c | 8 +++++---
>   1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/iommu/mtk_iommu.c b/drivers/iommu/mtk_iommu.c
> index db7d43adb06b..89cec51405cd 100644
> --- a/drivers/iommu/mtk_iommu.c
> +++ b/drivers/iommu/mtk_iommu.c
> @@ -506,7 +506,12 @@ static size_t mtk_iommu_unmap(struct iommu_domain *domain,
>   			      struct iommu_iotlb_gather *gather)
>   {
>   	struct mtk_iommu_domain *dom = to_mtk_domain(domain);
> +	unsigned long long end = iova + size;
>   
> +	if (gather->start > iova)
> +		gather->start = iova;
> +	if (gather->end < end)
> +		gather->end = end;
>   	return dom->iop->unmap(dom->iop, iova, size, gather);
>   }
>   
> @@ -523,9 +528,6 @@ static void mtk_iommu_iotlb_sync(struct iommu_domain *domain,
>   	struct mtk_iommu_domain *dom = to_mtk_domain(domain);
>   	size_t length = gather->end - gather->start;
>   
> -	if (gather->start == ULONG_MAX)
> -		return;
> -
>   	mtk_iommu_tlb_flush_range_sync(gather->start, length, gather->pgsize,
>   				       dom->data);
>   }
>