To: Andrew Morton <akpm@osdl.org>
Cc: Adrian Bunk <bunk@stusta.de>, Tom Tucker <tom@opengridcomputing.com>,
       Steve Wise <swise@opengridcomputing.com>,
       Roland Dreier <rolandd@cisco.com>, linux-kernel@vger.kernel.org,
       openib-general@openib.org
Subject: Re: 2.6.18-rc5-mm1: drivers/infiniband/hw/amso1100/c2.c compile error
References: <20060901015818.42767813.akpm@osdl.org>
	<20060901160023.GB18276@stusta.de>
	<20060901101340.962150cb.akpm@osdl.org>
From: Roland Dreier <rdreier@cisco.com>
Date: Fri, 01 Sep 2006 10:34:24 -0700
In-Reply-To: <20060901101340.962150cb.akpm@osdl.org> (Andrew Morton's message of "Fri, 1 Sep 2006 10:13:40 -0700")
Message-ID: <adak64nij8f.fsf@cisco.com>
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    Andrew> What's __raw_writeq() supposed to do, anyway?  On alpha
    Andrew> it's writeq() without an mb().  On parisc it's writeq()
    Andrew> only the data is byte-reversed.  On sparc64() it's
    Andrew> incomprehensible.  On everything else it's writeq().

My understanding is that __raw_writeq() is like writeq() except not
strongly ordered and without the byte-swap on big-endian
architectures.  The __raw_writeX() variants are convenient to avoid
having to write inefficient code like writel(swab32(foo), ...) when
talking to a PCI device that wants big-endian data.  Without the raw
variant, you end up with a double swap on big-endian architectures.

sparc64 looks wrong, since __raw_writeq() seems identical to writeq(),
which seems to imply it's going to swab what is stores.

 - R.
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