linux-kernel - Re: [PATCH v2] arm64/mm: Correct the cache line size warning with non coherent device

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Message-ID: <20190617162233.GB34565@arrakis.emea.arm.com>
Date:   Mon, 17 Jun 2019 17:22:33 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Zhangshaokun <zhangshaokun@...ilicon.com>
Cc:     Masayoshi Mizuma <msys.mizuma@...il.com>,
        Robin Murphy <robin.murphy@....com>,
        Will Deacon <will.deacon@....com>,
        linux-arm-kernel@...ts.infradead.org,
        Masayoshi Mizuma <m.mizuma@...fujitsu.com>,
        linux-kernel@...r.kernel.org,
        Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
        Zhang Lei <zhang.lei@...fujitsu.com>
Subject: Re: [PATCH v2] arm64/mm: Correct the cache line size warning with
 non coherent device

On Mon, Jun 17, 2019 at 07:00:34PM +0800, Zhangshaokun wrote:
> On 2019/6/17 18:45, Catalin Marinas wrote:
> > On Sat, Jun 15, 2019 at 10:44:33AM +0800, Zhangshaokun wrote:
> >> On 2019/6/14 21:11, Masayoshi Mizuma wrote:
> >>> diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
> >>> index 1669618db08a..379589dc7113 100644
> >>> --- a/arch/arm64/mm/dma-mapping.c
> >>> +++ b/arch/arm64/mm/dma-mapping.c
> >>> @@ -38,10 +38,6 @@ void arch_dma_prep_coherent(struct page *page, size_t size)
> >>>  
> >>>  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);
> >>> @@ -56,7 +52,17 @@ void arch_teardown_dma_ops(struct device *dev)
> >>>  void arch_setup_dma_ops(struct device *dev, u64 dma_base, u64 size,
> >>>  			const struct iommu_ops *iommu, bool coherent)
> >>>  {
> >>> +	int cls = cache_line_size_of_cpu();
> >>
> >> whether we need this local variable, how about use cache_line_size_of_cpu
> >> directly in WARN_TAINT just like before.
> > 
> > The reason being?
> 
> Since it is inline function,  maybe it is unnecessary, it is trivial.

OTOH, you end up with two reads from the CTR_EL0 register.

-- 
Catalin