Re: [PATCH v3 6/7] iommu/mediatek: Gather iova in iommu_unmap to achieve tlb sync once

[Robin Murphy]

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@xxxxxxx>

> Signed-off-by: Yong Wu <yong.wu@xxxxxxxxxxxx>
> ---
>   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);
>   }