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

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Date:	Fri, 2 May 2008 17:31:50 -0600
From:	"Moore, Eric" <Eric.Moore@....com>
To:	"Roland Dreier" <rdreier@...co.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??

On Friday, May 02, 2008 5:22 PM,  Roland Dreier wrote:
>  > 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.
> 

Thanks for the code sample.   Yes, I need to send a single atomic 64-bit
transaction.

Eric
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