linux-kernel - Re: [PATCH 1/1] edac x38: new MC driver module

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Date:	Tue, 11 Nov 2008 15:11:40 +0900
From:	Paul Mundt <lethal@...ux-sh.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Hitoshi Mitake <h.mitake@...il.com>,
	Hitoshi Mitake <mitake@...stcom.com>,
	Doug Thompson <norsk5@...oo.com>, dougthompson@...ssion.com,
	linux-kernel@...r.kernel.org, ktaka@...stcom.com,
	linux-arch@...r.kernel.org
Subject: Re: [PATCH 1/1] edac x38: new MC driver module

On Sun, Nov 09, 2008 at 11:26:46AM -0800, Andrew Morton wrote:
> (cc linux-arch)
> 
> > It seems that architectures that provide readq/writeq are
> > mips, parisc and x86 (and x86_64).
> > 
There are more than that, grep arch/*/include also.

In addition to mips, parisc, and x86, there is ia64, alpha, sh, and
sparc.

> #ifdef readq
> 
> Is a suitable way of determining whether the architecture implements
> readq and writeq.  It isn't pretty, but it will suffice.
> 
> A problem with it is that drivers will then do
> 
> #ifndef readq
> <provide a local implementation here>
> #endif
> 
> which rather sucks - we don't want lots of little private readq/writeq
> implementations all over the tree.
> 
> Perhaps it would be better to have a CONFIG_ARCH_HAS_READQ and to then
> disable these drivers on the architectures which don't provide
> readq/writeq support.
> 
However this is handled, we don't want a rehash of the read/writes{b,w,l} fiasco.

Allowing drivers to do their own local implementations of these things
has always been a complete disaster. A Kconfig option will at least take
care of having these craptastic ifdef lists for architectures in every
driver that rolls its own implementation.

Even a sub-optimal asm-generic version would be preferable, if the
semantics are well enough defined and consistently adhered to.
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