USB: mutual exclusion for EHCI init and port resets

This patch (as999) fixes a problem that sometimes shows up when host
controller driver modules are loaded in the wrong order.  If ehci-hcd
happens to initialize an EHCI controller while the companion OHCI or
UHCI controller is in the middle of a port reset, the reset can fail
and the companion may get very confused.  The patch adds an
rw-semaphore and uses it to keep EHCI initialization and port resets
mutually exclusive.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Acked-by: David Brownell <david-b@pacbell.net>
Cc: David Miller <davem@davemloft.net>
Cc: Dely L Sy <dely.l.sy@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 8 insertions, 0 deletions

diff --git a/drivers/usb/host/ehci-hcd.c b/drivers/usb/host/ehci-hcd.c
index db00492588b6..c1514442883e 100644
--- a/drivers/usb/host/ehci-hcd.c
+++ b/drivers/usb/host/ehci-hcd.c
@@ -570,10 +570,18 @@ static int ehci_run (struct usb_hcd *hcd)
          * are explicitly handed to companion controller(s), so no TT is
          * involved with the root hub.  (Except where one is integrated,
          * and there's no companion controller unless maybe for USB OTG.)
+         *
+         * Turning on the CF flag will transfer ownership of all ports
+         * 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.
          */
+        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 */
+        up_write(&ehci_cf_port_reset_rwsem);
 
         temp = HC_VERSION(ehci_readl(ehci, &ehci->caps->hc_capbase));
         ehci_info (ehci,