linux-kernel - Re: [patch 19/26] USB: mutual exclusion for EHCI init and port resets

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Message-Id: <20071119184128.E43D423C403@adsl-69-226-248-13.dsl.pltn13.pacbell.net>
Date:	Mon, 19 Nov 2007 10:41:28 -0800
From:	David Brownell <david-b@...bell.net>
To:	stable@...nel.org, linux-usb-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org, gregkh@...e.de
Cc:	zwane@....linux.org.uk, tytso@....edu,
	torvalds@...ux-foundation.org, stern@...land.harvard.edu,
	reviews@...cw.f00f.org, rdunlap@...otime.net, mkrufky@...uxtv.org,
	jmforbes@...uxtx.org, dely.l.sy@...el.com, davem@...emloft.net,
	davej@...hat.com, chuckw@...ntumlinux.com, cebbert@...hat.com,
	cavokz@...il.com, alan@...rguk.ukuu.org.uk,
	akpm@...ux-foundation.org
Subject: Re: [patch 19/26] USB: mutual exclusion for EHCI init and port resets

Still needs the following update, IMO ... 

======	CUT HERE
A recent patch added software synchronization during EHCI startup,
so ports aren't switched away from the companion controllers after
resets have started.  This patch adds a short delay letting hardware
get a chance to finish that port switching before any new resets begin.

That is, both sides of that hardware race window need to be closed.

Signed-off-by: David Brownell <dbrownell@...rs.sourceforge.net>
---
 drivers/usb/host/ehci-hcd.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- g26.orig/drivers/usb/host/ehci-hcd.c	2007-11-13 16:07:12.000000000 -0800
+++ g26/drivers/usb/host/ehci-hcd.c	2007-11-13 16:13:01.000000000 -0800
@@ -594,12 +594,15 @@ static int ehci_run (struct usb_hcd *hcd
 	 * from the companions to the EHCI controller.  If any of the
 	 * companions are in the middle of a port reset at the time, it
 	 * could cause trouble.  Write-locking ehci_cf_port_reset_rwsem
-	 * guarantees that no resets are in progress.
+	 * guarantees that no resets are in progress.  After we set CF,
+	 * a short delay lets the hardware catch up; new resets shouldn't
+	 * start before the port switching actions complete.
 	 */
 	down_write(&ehci_cf_port_reset_rwsem);
 	hcd->state = HC_STATE_RUNNING;
 	ehci_writel(ehci, FLAG_CF, &ehci->regs->configured_flag);
 	ehci_readl(ehci, &ehci->regs->command);	/* unblock posted writes */
+	msleep(5);
 	up_write(&ehci_cf_port_reset_rwsem);
 
 	temp = HC_VERSION(ehci_readl(ehci, &ehci->caps->hc_capbase));
-
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