linux-kernel - Re: 2.6.18-rc5-mm1: drivers/infiniband/hw/amso1100/c2.c compile error

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Message-ID: <adak64nij8f.fsf@cisco.com>
Date:	Fri, 01 Sep 2006 10:34:24 -0700
From:	Roland Dreier <rdreier@...co.com>
To:	Andrew Morton <akpm@...l.org>
Cc:	Adrian Bunk <bunk@...sta.de>,
	Tom Tucker <tom@...ngridcomputing.com>,
	Steve Wise <swise@...ngridcomputing.com>,
	Roland Dreier <rolandd@...co.com>,
	linux-kernel@...r.kernel.org, openib-general@...nib.org
Subject: Re: 2.6.18-rc5-mm1: drivers/infiniband/hw/amso1100/c2.c compile error

    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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