linux-kernel - Re: [PATCH RFC v2 8/8] dma-iommu: Support DMA sync batch mode for iommu_dma_sync_sg_for

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Message-ID: <20251227201642.GQ11869@unreal>
Date: Sat, 27 Dec 2025 22:16:42 +0200
From: Leon Romanovsky <leon@...nel.org>
To: Barry Song <21cnbao@...il.com>
Cc: catalin.marinas@....com, m.szyprowski@...sung.com, robin.murphy@....com,
	will@...nel.org, iommu@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	xen-devel@...ts.xenproject.org, Barry Song <baohua@...nel.org>,
	Ada Couprie Diaz <ada.coupriediaz@....com>,
	Ard Biesheuvel <ardb@...nel.org>, Marc Zyngier <maz@...nel.org>,
	Anshuman Khandual <anshuman.khandual@....com>,
	Ryan Roberts <ryan.roberts@....com>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Joerg Roedel <joro@...tes.org>,
	Tangquan Zheng <zhengtangquan@...o.com>
Subject: Re: [PATCH RFC v2 8/8] dma-iommu: Support DMA sync batch mode for
 iommu_dma_sync_sg_for_{cpu, device}

On Sat, Dec 27, 2025 at 11:52:48AM +1300, Barry Song wrote:
> From: Barry Song <baohua@...nel.org>
> 
> Apply batched DMA synchronization to iommu_dma_sync_sg_for_cpu() and
> iommu_dma_sync_sg_for_device(). For all buffers in an SG list, only
> a single flush operation is needed.
> 
> I do not have the hardware to test this, so the patch is marked as
> RFC. I would greatly appreciate any testing feedback.
> 
> Cc: Leon Romanovsky <leon@...nel.org>
> Cc: Marek Szyprowski <m.szyprowski@...sung.com>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Ada Couprie Diaz <ada.coupriediaz@....com>
> Cc: Ard Biesheuvel <ardb@...nel.org>
> Cc: Marc Zyngier <maz@...nel.org>
> Cc: Anshuman Khandual <anshuman.khandual@....com>
> Cc: Ryan Roberts <ryan.roberts@....com>
> Cc: Suren Baghdasaryan <surenb@...gle.com>
> Cc: Robin Murphy <robin.murphy@....com>
> Cc: Joerg Roedel <joro@...tes.org>
> Cc: Tangquan Zheng <zhengtangquan@...o.com>
> Signed-off-by: Barry Song <baohua@...nel.org>
> ---
>  drivers/iommu/dma-iommu.c | 15 +++++++--------
>  1 file changed, 7 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> index ffa940bdbbaf..b68dbfcb7846 100644
> --- a/drivers/iommu/dma-iommu.c
> +++ b/drivers/iommu/dma-iommu.c
> @@ -1131,10 +1131,9 @@ void iommu_dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sgl,
>  			iommu_dma_sync_single_for_cpu(dev, sg_dma_address(sg),
>  						      sg->length, dir);
>  	} else if (!dev_is_dma_coherent(dev)) {
> -		for_each_sg(sgl, sg, nelems, i) {
> +		for_each_sg(sgl, sg, nelems, i)
>  			arch_sync_dma_for_cpu(sg_phys(sg), sg->length, dir);
> -			arch_sync_dma_flush();
> -		}
> +		arch_sync_dma_flush();

This and previous patches should be squashed into the one which
introduced arch_sync_dma_flush().

Thanks