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

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Date:   Mon, 17 Jun 2019 19:00:34 +0800
From:   Zhangshaokun <zhangshaokun@...ilicon.com>
To:     Catalin Marinas <catalin.marinas@....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

Hi Catalin,

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/kernel/cacheinfo.c b/arch/arm64/kernel/cacheinfo.c
>>> index 6eaf1c07aa4e..7fa6828bb488 100644
>>> --- a/arch/arm64/kernel/cacheinfo.c
>>> +++ b/arch/arm64/kernel/cacheinfo.c
>>> @@ -19,12 +19,10 @@
>>>  
>>>  int cache_line_size(void)
>>>  {
>>> -	u32 cwg = cache_type_cwg();
>>> -
>>>  	if (coherency_max_size != 0)
>>>  		return coherency_max_size;
>>>  
>>> -	return cwg ? 4 << cwg : ARCH_DMA_MINALIGN;
>>> +	return cache_line_size_of_cpu();
>>>  }
>>
>> How about simplify it as this?
>>
>> int cache_line_size(void)
>> {
>>         return coherency_max_size ? coherency_max_size :
>>                 cache_line_size_of_cpu();
>> }
> 
> I don't see this as a simplification, easier to read with explicit 'if'.
> 

Okay, I thought it can save some unnecessary lines :-).

>>>  EXPORT_SYMBOL_GPL(cache_line_size);
>>>  
>>> 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.

> Anyway, I'll queue v2 of this patch as is for 5.3. Thanks.
> 

It's fine.

Thanks,
Shaokun