linux-kernel - Re: [Suggestion] arch/*/include/asm/bitops.h: about __set

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Date:	Thu, 13 Jun 2013 10:43:51 +0800
From:	Chen Gang <gang.chen@...anux.com>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
CC:	Tony Luck <tony.luck@...il.com>,
	Richard Henderson <rth@...ddle.net>,
	Ivan Kokshaysky <ink@...assic.park.msu.ru>,
	Matt Turner <mattst88@...il.com>,
	"dhowells@...hat.com" <dhowells@...hat.com>,
	"Yu, Fenghua" <fenghua.yu@...el.com>,
	Koichi Yasutake <yasutake.koichi@...panasonic.com>,
	alpha <linux-alpha@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-ia64@...r.kernel.org" <linux-ia64@...r.kernel.org>,
	linux-am33-list@...hat.com, Linux-Arch <linux-arch@...r.kernel.org>
Subject: Re: [Suggestion] arch/*/include/asm/bitops.h: about __set_bit() API.

On 06/11/2013 03:32 PM, Geert Uytterhoeven wrote:
> On Tue, Jun 11, 2013 at 12:26 AM, Tony Luck <tony.luck@...il.com> wrote:
>> > On Sat, Jun 8, 2013 at 3:08 AM, Chen Gang <gang.chen@...anux.com> wrote:
>>> >> using 'unsigned int *', implicitly:
>>> >>   ./ia64/include/asm/bitops.h:63:__set_bit (int nr, volatile void *addr)
>> >
>> > There is some downside on ia64 to your suggestion.  If "addr" is properly
>> > aligned for an "int", but misaligned for a long ... i.e. addr%8 == 4, then I'll
>> > take an unaligned reference trap if I work with long* where the current code
>> > working with int* does not.
>> >
>> > Now perhaps all the callers do guarantee long* alignment?  But I don't know.
>> >
>> > Apart from uniformity, there doesn't see to be any upside to changing this.
> The address pointers have been supposed to be "long *" for a very long time.
> Probably alpha (the second official Linux platform) did it
> differently, and never
> standardized to "long *".

Excuse me, I am not quite familiar with the details, but I guess, it is
about functional feature issues, not (or not only) about bug issues.

For the architectures which can fully support 64-bit OS, excluding ia64
and alpha, all of them can support setting 64 bits (from 0 to 63) under
64-bit machine.

I am not quite sure whether any sub-systems have already set higher bit
(> 31) under 64-bit machine, but in the future, it seems they could (at
least our API supposed so).


Thanks.
-- 
Chen Gang

Asianux Corporation
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