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

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Date:   Thu, 29 Nov 2018 14:38:59 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Jose Abreu' <jose.abreu@...opsys.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}()

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.

	David

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