linux-kernel - Re: HELP: Is writeq an atomic operation??

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Date:	Fri, 02 May 2008 16:21:46 -0700
From:	Roland Dreier <rdreier@...co.com>
To:	"Moore\, Eric" <Eric.Moore@....com>
Cc:	"David Miller" <davem@...emloft.net>, <linux-scsi@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: HELP: Is writeq an atomic operation??

 > Yeah,  I forgot I have a #ifndef writeq, then defined the x86_64 version
 > of that.   I've not tested on x86, so I'm not sure whether it works.
 > How are you handling writeq when its not defined, as the case in x86?

Write two writel() inside a spinlock to avoid any transactions in the
middle (the HW I'm dealing with can deal with two 32-bit transactions,
as long as nothing comes in the middle).  If your hardware demands a
single 64-bit transaction, you may be in trouble, because I'm not sure
all 32-bit systems can generate such a PCIe transaction.

You can see include/linux/mlx4/doorbell.h for exactly what I did.

 - R.
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