linux-kernel - Re: [PATCH v3 1/3] asm-generic/io.h: Implement generic {read,write}s*()

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Date:	Thu, 17 Jul 2014 13:01:22 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Thierry Reding <thierry.reding@...il.com>
Cc:	Russell King <linux@....linux.org.uk>,
	Will Deacon <Will.Deacon@....com>,
	Arnd Bergmann <arnd@...db.de>,
	Stephen Boyd <sboyd@...eaurora.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/3] asm-generic/io.h: Implement generic
 {read,write}s*()

On Wed, Jul 16, 2014 at 12:01:22PM +0100, Thierry Reding wrote:
> From: Thierry Reding <treding@...dia.com>
> 
> Currently driver writers need to use io{read,write}{8,16,32}_rep() when
> accessing FIFO registers portably. This is bad for two reasons: it is
> inconsistent with how other registers are accessed using the standard
> {read,write}{b,w,l}() functions, which can lead to confusion. On some
> architectures the io{read,write}*() functions also need to perform some
> extra checks to determine whether an address is memory-mapped or refers
> to I/O space. Drivers which can be expected to never use I/O can safely
> use the {read,write}s{b,w,l,q}(), just like they use their non-string
> variants and there's no need for these extra checks.
> 
> This patch implements generic versions of readsb(), readsw(), readsl(),
> readsq(), writesb(), writesw(), writesl() and writesq(). Variants of
> these string functions for I/O accesses (ins*() and outs*() as well as
> ioread*_rep() and iowrite*_rep()) are now implemented in terms of the
> new functions.
> 
> Going forward, {read,write}{,s}{b,w,l,q}() should be used consistently
> by drivers for devices that will only ever be memory-mapped and hence
> don't need to access I/O space, whereas io{read,write}{8,16,32}_rep()
> should be used by drivers for devices that can be either memory-mapped
> or I/O-mapped.
> 
> While at it, also make sure that any of the functions provided as
> fallback for architectures that don't override them can't be overridden
> subsequently.
> 
> This is compile- and runtime-tested on 32-bit and 64-bit ARM and compile
> tested on Microblaze, s390, SPARC and Xtensa. For ARC, Blackfin, Metag,
> OpenRISC, Score and Unicore32 which also use asm-generic/io.h I couldn't
> find or build a cross-compiler that would run on my system. But by code
> inspection they shouldn't break with this patch.
> 
> Signed-off-by: Thierry Reding <treding@...dia.com>

Acked-by: Catalin Marinas <catalin.marinas@....com>
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