linux-kernel - Re: [PATCH 4/5] iommu/rockchip: add ARM64 cache flush operation for iommu

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Message-ID: <20160524095927.GS4892@e104818-lin.cambridge.arm.com>
Date:	Tue, 24 May 2016 10:59:27 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Shunqian Zheng <zhengsq@...k-chips.com>
Cc:	Robin Murphy <robin.murphy@....com>, joro@...tes.org,
	heiko@...ech.de, Mark Rutland <mark.rutland@....com>,
	linux-rockchip@...ts.infradead.org,
	iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	Simon <xxm@...k-chips.com>
Subject: Re: [PATCH 4/5] iommu/rockchip: add ARM64 cache flush operation for
 iommu

On Tue, May 24, 2016 at 10:31:17AM +0800, Shunqian Zheng wrote:
> On 2016年05月23日 21:35, Catalin Marinas wrote:
> >On Mon, May 23, 2016 at 11:44:14AM +0100, Robin Murphy wrote:
> >>On 23/05/16 02:37, Shunqian Zheng wrote:
> >>>From: Simon <xxm@...k-chips.com>
> >>>
> >>>Signed-off-by: Simon <xxm@...k-chips.com>
> >>>---
> >>>  drivers/iommu/rockchip-iommu.c | 4 ++++
> >>>  1 file changed, 4 insertions(+)
> >>>
> >>>diff --git a/drivers/iommu/rockchip-iommu.c b/drivers/iommu/rockchip-iommu.c
> >>>index 043d18c..1741b65 100644
> >>>--- a/drivers/iommu/rockchip-iommu.c
> >>>+++ b/drivers/iommu/rockchip-iommu.c
> >>>@@ -95,12 +95,16 @@ struct rk_iommu {
> >>>
> >>>  static inline void rk_table_flush(u32 *va, unsigned int count)
> >>>  {
> >>>+#if defined(CONFIG_ARM)
> >>>  	phys_addr_t pa_start = virt_to_phys(va);
> >>>  	phys_addr_t pa_end = virt_to_phys(va + count);
> >>>  	size_t size = pa_end - pa_start;
> >>>
> >>>  	__cpuc_flush_dcache_area(va, size);
> >>>  	outer_flush_range(pa_start, pa_end);
> >>>+#elif defined(CONFIG_ARM64)
> >>>+	__dma_flush_range(va, va + count);
> >>>+#endif
> >>Ugh, please don't use arch-private cache maintenance functions directly from
> >>a driver. Allocating/mapping page tables to be read by the IOMMU is still
> >>DMA, so using the DMA APIs is the correct way to manage them, *especially*
> >>if it needs to work across multiple architectures.
> 
> It's easier for us if changing  the __dma_flush_range() to
> __flush_dcache_area() is acceptable here?

It's not really acceptable for arm64, nor for arm32. Please fix this
driver in a similar way to commit e3c971960fd4 ("iommu/tegra-smmu:
Convert to use DMA API").

The only place where we allowed __flush_dcache_area() is in the GICv3
driver and that's because it hasn't been wired as a platform device
(yet).

-- 
Catalin