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Date:   Tue, 11 Jun 2019 19:00:07 +0100
From:   Catalin Marinas <catalin.marinas@arm.com>
To:     Masayoshi Mizuma <msys.mizuma@gmail.com>
Cc:     Will Deacon <will.deacon@arm.com>,
        linux-arm-kernel@lists.infradead.org,
        Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>,
        linux-kernel@vger.kernel.org,
        Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>,
        Zhang Lei <zhang.lei@jp.fujitsu.com>,
        Robin Murphy <robin.murphy@arm.com>
Subject: Re: [PATCH 1/2] arm64/mm: check cpu cache line size with
 non-coherent device
Message-ID: <20190611180007.him7md7gdcjs5cg6@mbp>
References: <20190611151731.6135-1-msys.mizuma@gmail.com>
 <20190611151731.6135-2-msys.mizuma@gmail.com>
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On Tue, Jun 11, 2019 at 11:17:30AM -0400, Masayoshi Mizuma wrote:
> --- a/arch/arm64/mm/dma-mapping.c
> +++ b/arch/arm64/mm/dma-mapping.c
> @@ -91,10 +91,6 @@ static int __swiotlb_mmap_pfn(struct vm_area_struct *vma,
>  
>  static int __init arm64_dma_init(void)
>  {
> -	WARN_TAINT(ARCH_DMA_MINALIGN < cache_line_size(),
> -		   TAINT_CPU_OUT_OF_SPEC,
> -		   "ARCH_DMA_MINALIGN smaller than CTR_EL0.CWG (%d < %d)",
> -		   ARCH_DMA_MINALIGN, cache_line_size());
>  	return dma_atomic_pool_init(GFP_DMA32, __pgprot(PROT_NORMAL_NC));
>  }
>  arch_initcall(arm64_dma_init);
> @@ -473,6 +469,11 @@ void arch_setup_dma_ops(struct device *dev, u64 dma_base, u64 size,
>  			const struct iommu_ops *iommu, bool coherent)
>  {
>  	dev->dma_coherent = coherent;
> +
> +	if (!coherent && (cache_line_size() > ARCH_DMA_MINALIGN))
> +		dev_WARN(dev, "ARCH_DMA_MINALIGN smaller than CTR_EL0.CWG (%d < %d)",
> +				ARCH_DMA_MINALIGN, cache_line_size());

I'm ok in principle with this patch, with the minor issue that since
commit 7b8c87b297a7 ("arm64: cacheinfo: Update cache_line_size detected
from DT or PPTT") queued for 5.3 cache_line_size() gets the information
from DT or ACPI. The reason for this change is that the information is
used for performance tuning rather than DMA coherency.

You can go for a direct cache_type_cwg() check in here, unless Robin
(cc'ed) has a better idea.

-- 
Catalin