Re: [PATCH] UHCI: add missing memory barriers

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Fri, 2005-12-16 at 11:59 -0800, Linux Kernel Mailing List wrote:
> tree d094f197975af7ef7b80006dbea0f5d38915f88b
> parent 42f3ab42875a52af7e711803bfb8d8d7cca84c1c
> author Alan Stern <stern@rowland.harvard.edu> Sat, 17 Dec 2005 03:09:01 -0800
> committer Linus Torvalds <torvalds@g5.osdl.org> Sat, 17 Dec 2005 03:25:25 -0800
> 
> [PATCH] UHCI: add missing memory barriers
> 
> This patch (as617) adds a couple of memory barriers that Ben H. forgot in
> his recent suspend/resume fix.

I didn't think they were necessary but they certainly won't hurt and
it's not a hot code path...

>  	pci_write_config_word(to_pci_dev(uhci_dev(uhci)), USBLEGSUP, 0);
> +	mb();

Isn't pci config space access always fully synchronous ?

>  	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();

I don't think that one matters much but it won't hurt for sure.

>  	if (uhci->rh_state == UHCI_RH_RESET)	/* Dead */
>  		return 0;
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