RE: HELP: Is writeq an atomic operation??

Moore, Eric
2008-05-02T23:32:38Z

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