Re: [PATCH 4/7] io-64-nonatomic: Add relaxed accessor variants

[Robin Murphy <robin.murphy-5wv7dgnIgG8@public.gmane.org>]

On 21/04/16 17:18, Will Deacon wrote:
> On Wed, Apr 13, 2016 at 06:13:00PM +0100, Robin Murphy wrote:
>> Whilst commit 9439eb3ab9d1 ("asm-generic: io: implement relaxed
>> accessor macros as conditional wrappers") makes the *_relaxed forms of
>> I/O accessors universally available to drivers, in cases where writeq()
>> is implemented via the io-64-nonatomic helpers, writeq_relaxed() will
>> end up falling back to writel() regardless of whether writel_relaxed()
>> is available (identically for s/write/read/).
>>
>> Add corresponding relaxed forms of the nonatomic helpers to delegate
>> to the equivalent 32-bit accessors as appropriate.
>>
>> CC: Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org>
>> CC: Christoph Hellwig <hch-jcswGhMUV9g@public.gmane.org>
>> CC: Darren Hart <dvhart-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
>> CC: Hitoshi Mitake <mitake.hitoshi-Zyj7fXuS5i5L9jVzuh4AOg@public.gmane.org>
>> Signed-off-by: Robin Murphy <robin.murphy-5wv7dgnIgG8@public.gmane.org>
>> ---
>>   include/linux/io-64-nonatomic-hi-lo.h | 25 +++++++++++++++++++++++++
>>   include/linux/io-64-nonatomic-lo-hi.h | 25 +++++++++++++++++++++++++
>>   2 files changed, 50 insertions(+)
>>
>> diff --git a/include/linux/io-64-nonatomic-hi-lo.h b/include/linux/io-64-nonatomic-hi-lo.h
>> index 11d7e84..1a85566 100644
>> --- a/include/linux/io-64-nonatomic-hi-lo.h
>> +++ b/include/linux/io-64-nonatomic-hi-lo.h
>> @@ -21,6 +21,23 @@ static inline void hi_lo_writeq(__u64 val, volatile void __iomem *addr)
>>   	writel(val, addr);
>>   }
>>
>> +static inline __u64 hi_lo_readq_relaxed(const volatile void __iomem *addr)
>> +{
>> +	const volatile u32 __iomem *p = addr;
>> +	u32 low, high;
>> +
>> +	high = readl_relaxed(p + 1);
>> +	low = readl_relaxed(p);
>> +
>> +	return low + ((u64)high << 32);
>> +}
>> +
>> +static inline void hi_lo_writeq_relaxed(__u64 val, volatile void __iomem *addr)
>> +{
>> +	writel_relaxed(val >> 32, addr + 4);
>> +	writel_relaxed(val, addr);
>> +}
>
> Could we not generate the _relaxed variants with some macro magic?

We _could_ - indeed I started doing that, but then decided that the 
obfuscation of horrible macro-templated functions wasn't worth saving a 
couple of hundred bytes in some code that isn't exactly difficult to 
maintain and has needed touching once in 4 years.

If you did want to go down the macro route, I may as well also generate 
both lo-hi and hi-lo headers all from a single template, it'd be really 
clever... <alarm bells> ;)

Robin.

>
> Will
>