Re: [patch 4/4] UHCI: add missing memory barriers

Jeff Garzik
2005-12-13T00:27:59Z

Greg Kroah-Hartman wrote:
> From: Alan Stern <stern@rowland.harvard.edu>
>
> This patch (as617) adds a couple of memory barriers that Ben H. forgot in
> his recent suspend/resume fix.
>
> Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
>
> ---
> drivers/usb/host/uhci-hcd.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> --- greg-2.6.orig/drivers/usb/host/uhci-hcd.c
> +++ greg-2.6/drivers/usb/host/uhci-hcd.c
> @@ -717,6 +717,7 @@ static int uhci_suspend(struct usb_hcd *
> * at the source, so we must turn off PIRQ.
> */
> pci_write_config_word(to_pci_dev(uhci_dev(uhci)), USBLEGSUP, 0);
> + mb();
> clear_bit(HCD_FLAG_HW_ACCESSIBLE, &hcd->flags);
> uhci->hc_inaccessible = 1;
> hcd->poll_rh = 0;
> @@ -738,6 +739,7 @@ static int uhci_resume(struct usb_hcd *h
> * really don't want to keep a stale HCD_FLAG_HW_ACCESSIBLE=0
> */
> set_bit(HCD_FLAG_HW_ACCESSIBLE, &hcd->flags);
> + mb();

Are these just guesses, or what?

Why not smp_mb__before_clear_bit() or smp_mb__after_clear_bit() ?

Jeff