linux-kernel - Re: Opinion on ordering of writel vs. stores to RAM

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Date:	Tue, 12 Sep 2006 18:47:29 +0200
From:	Segher Boessenkool <segher@...nel.crashing.org>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	David Miller <davem@...emloft.net>, jbarnes@...tuousgeek.org,
	jeff@...zik.org, paulus@...ba.org, torvalds@...l.org,
	linux-kernel@...r.kernel.org, akpm@...l.org
Subject: Re: Opinion on ordering of writel vs. stores to RAM

> As Paulus also pointed out, having writel() behave differently  
> based on
> some magic done earlier at map time makes it harder to understand what
> happens when reading the code, and thus harder to audit drivers for
> missing barriers etc... since it's not obvious at first sight wether a
> driver is using ordered or relaxed semantics.

I do not buy this argument because I do not believe you
can "audit" a driver at "first sight".  You'll have to
look at the mapping call anyway, something might be wrong
there (playing evil __ioremap() tricks, mapping the wrong
size, whatever).

I do see your point, I don't believe the ramifications are
as severe as you make them to be though, esp. when compared
to all the (readability, auditing!) problems that having
more different interfaces for basically the same thing will
bring us.

Segher

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