linux-kernel - Re: [RFC PATCH 5/5] dma-mapping: Allow batched DMA sync operations if supported by the arch

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Message-Id: <20251121232807.40491-1-21cnbao@gmail.com>
Date: Sat, 22 Nov 2025 07:28:07 +0800
From: Barry Song <21cnbao@...il.com>
To: m.szyprowski@...sung.com
Cc: 21cnbao@...il.com,
	ada.coupriediaz@....com,
	anshuman.khandual@....com,
	ardb@...nel.org,
	catalin.marinas@....com,
	iommu@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	maz@...nel.org,
	robin.murphy@....com,
	ryan.roberts@....com,
	surenb@...gle.com,
	v-songbaohua@...o.com,
	will@...nel.org,
	zhengtangquan@...o.com
Subject: Re: [RFC PATCH 5/5] dma-mapping: Allow batched DMA sync operations if supported by the arch

On Sat, Nov 22, 2025 at 12:09 AM Marek Szyprowski <m.szyprowski@...sung.com> wrote:
>
> Hi Barry,
>
[...]
> This version looks a bit better to me. Similar batching could be added
> also to dma_iova_link()/dma_iova_sync() paths.

Thanks, Marek. I will respin a new version. For dma_iova, I assume you meant
something like the following?

diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index 7944a3af4545..7bb6ed663236 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -1837,7 +1837,7 @@ static int __dma_iova_link(struct device *dev, dma_addr_t addr,
 	int prot = dma_info_to_prot(dir, coherent, attrs);
 
 	if (!coherent && !(attrs & (DMA_ATTR_SKIP_CPU_SYNC | DMA_ATTR_MMIO)))
-		arch_sync_dma_for_device(phys, size, dir);
+		arch_sync_dma_for_device_batch_add(phys, size, dir);
 
 	return iommu_map_nosync(iommu_get_dma_domain(dev), addr, phys, size,
 			prot, GFP_ATOMIC);
@@ -1980,6 +1980,8 @@ int dma_iova_sync(struct device *dev, struct dma_iova_state *state,
 	dma_addr_t addr = state->addr + offset;
 	size_t iova_start_pad = iova_offset(iovad, addr);
 
+	if (!dev_is_dma_coherent(dev))
+		arch_sync_dma_batch_flush();
 	return iommu_sync_map(domain, addr - iova_start_pad,
 		      iova_align(iovad, size + iova_start_pad));
 }

If so, I don't really have such hardware to test. I wonder if I can make it as
patch 6/6 when respinning, and still mark it as RFC v2. Or should I leave it as
is and expect someone with the hardware to test and send it?

Thanks
Barry