To: Andrew Morton <akpm@osdl.org>
Cc: "Bryan O'Sullivan" <bos@pathscale.com>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1 of 3] Introduce __raw_memcpy_toio32
References: <patchbomb.1136579193@eng-12.pathscale.com>
	<d286502c3b3cd6bcec7b.1136579194@eng-12.pathscale.com>
	<20060110011844.7a4a1f90.akpm@osdl.org>
From: Roland Dreier <rdreier@cisco.com>
Date: Tue, 10 Jan 2006 06:55:17 -0800
In-Reply-To: <20060110011844.7a4a1f90.akpm@osdl.org> (Andrew Morton's
 message of "Tue, 10 Jan 2006 01:18:44 -0800")
Message-ID: <adaslrw3zfu.fsf@cisco.com>
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    Bryan> This arch-independent routine copies data to a
    Bryan> memory-mapped I/O region, using 32-bit accesses.  It does
    Bryan> not guarantee access ordering, nor does it perform a memory
    Bryan> barrier afterwards.  This style of access is required by
    Bryan> some devices.

    Andrew> Not providing orderingor barriers makes this a rather
    Andrew> risky thing to export - people might use it, find their
    Andrew> driver "works" on one architecture, but fails on another.

    Andrew> I guess the "__" is a decent warning of this, and the
    Andrew> patch anticipates a higher-level raw_memcpy_toio32() which
    Andrew> implements those things, yes?

I suggested the __raw_ name to parallel __raw_writel and friends.  The
name for the version that ends with a write barrier would presumably
be just "memcpy_toio32()".  Bryan could easily add that his patch as
well, even though the Pathscale driver will only use the __raw_ version.

    Andrew> How come __raw_memcpy_toio32() is inlined?

That is a good question, especially since the optimized
x86_64-specific version is out-of-line.  I suspect the answer is
mainly that that's the easiest way to stick it in a header in
include/asm-generic.  I think it would be worth working a little
harder and making the generic version out-of-line.
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