linux-kernel - Re: x86: Is 'volatile' necessary for readb/writeb and friends?

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Date:	Fri, 4 Dec 2009 20:54:41 +0100 (CET)
From:	"Segher Boessenkool" <segher@...nel.crashing.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	"Segher Boessenkool" <segher@...nel.crashing.org>,
	"Ahmed S. Darwish" <darwish.07@...il.com>, x86@...nel.org,
	"Rusty Russell" <rusty@...tcorp.com.au>,
	"Ingo Molnar" <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: x86: Is 'volatile' necessary for readb/writeb and friends?

>>> static inline unsigned char readb(const volatile void __iomem *addr) {
>>
>> This "volatile" is meaningless.
>
> Wrong.  "volatile" here is an assertion that it is safe to pass pointer
> to a volatile object to this function.

Yes, sorry.  What I meant is: this volatile has no effect on what
the rest of the function does.

> Either way, it works, it is guaranteed to be safe, and removing it can
> only introduce bugs, not remove them.

Oh definitely, I wasn't suggesting otherwise.


Segher

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