linux-kernel - Re: [PATCH v2] ARC: io.h: Implement reads{x}()/writes{x}()

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Date:   Thu, 29 Nov 2018 14:42:29 +0000
From:   Jose Abreu <jose.abreu@...opsys.com>
To:     David Laight <David.Laight@...LAB.COM>,
        "linux-snps-arc@...ts.infradead.org" 
        <linux-snps-arc@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     Vineet Gupta <vineet.gupta1@...opsys.com>,
        Alexey Brodkin <alexey.brodkin@...opsys.com>,
        Joao Pinto <joao.pinto@...opsys.com>,
        "Vitor Soares" <vitor.soares@...opsys.com>
Subject: Re: [PATCH v2] ARC: io.h: Implement reads{x}()/writes{x}()

On 29-11-2018 14:38, David Laight wrote:
> From: Jose Abreu
>> Sent: 29 November 2018 14:29
>>
>> Some ARC CPU's do not support unaligned loads/stores. Currently, generic
>> implementation of reads{b/w/l}()/writes{b/w/l}() is being used with ARC.
>> This can lead to misfunction of some drivers as generic functions do a
>> plain dereference of a pointer that can be unaligned.
>>
>> Let's use {get/put}_unaligned() helper instead of plain dereference of
>> pointer in order to fix this.
> ...
>> +#define __raw_readsx(t,f) \
>> +static inline void __raw_reads##f(const volatile void __iomem *addr, \
>> +				  void *buffer, unsigned int count) \
>> +{ \
>> +	if (count) { \
>> +		const unsigned long bptr = (unsigned long)buffer; \
>> +		u##t *buf = buffer; \
>> +\
>> +		do { \
>> +			u##t x = __raw_read##f(addr); \
>> +\
>> +			/* Some ARC CPU's don't support unaligned accesses */ \
>> +			if (bptr % ((t) / 8)) { \
>> +				put_unaligned(x, buf++); \
>> +			} else { \
>> +				*buf++ = x; \
>> +			} \
>> +		} while (--count); \
>> +	} \
>> +}
> Does the compiler move the alignment test outside the loop?
> You really want two copies of the loop body.

Hmm, I would expect so because the if condition takes two const
args ... I will try check that.

Thanks and Best Regards,
Jose Miguel Abreu

>
> 	David
>
> -
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