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>

2 files changed, 21 insertions, 2 deletions

diff --git a/drivers/usb/core/hcd.h b/drivers/usb/core/hcd.h
index 1396141274f1..98e24194a4ab 100644
--- a/drivers/usb/core/hcd.h
+++ b/drivers/usb/core/hcd.h
@@ -19,6 +19,8 @@
 
 #ifdef __KERNEL__
 
+#include <linux/rwsem.h>
+
 /* This file contains declarations of usbcore internals that are mostly
  * used or exposed by Host Controller Drivers.
  */
@@ -470,5 +472,9 @@ static inline void usbmon_urb_complete(struct usb_bus *bus, struct urb *urb,
                 : (in_interrupt () ? "in_interrupt" : "can sleep"))
 
 
-#endif /* __KERNEL__ */
+/* This rwsem is for use only by the hub driver and ehci-hcd.
+ * Nobody else should touch it.
+ */
+extern struct rw_semaphore ehci_cf_port_reset_rwsem;
 
+#endif /* __KERNEL__ */
diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index 481dca641ea2..d20cb545a6e4 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -125,6 +125,12 @@ MODULE_PARM_DESC(use_both_schemes,
                 "try the other device initialization scheme if the "
                 "first one fails");
 
+/* Mutual exclusion for EHCI CF initialization.  This interferes with
+ * port reset on some companion controllers.
+ */
+DECLARE_RWSEM(ehci_cf_port_reset_rwsem);
+EXPORT_SYMBOL_GPL(ehci_cf_port_reset_rwsem);
+
 
 static inline char *portspeed(int portstatus)
 {
@@ -1581,6 +1587,11 @@ static int hub_port_reset(struct usb_hub *hub, int port1,
 {
         int i, status;
 
+        /* Block EHCI CF initialization during the port reset.
+         * Some companion controllers don't like it when they mix.
+         */
+        down_read(&ehci_cf_port_reset_rwsem);
+
         /* Reset the port */
         for (i = 0; i < PORT_RESET_TRIES; i++) {
                 status = set_port_feature(hub->hdev,
@@ -1612,7 +1623,7 @@ static int hub_port_reset(struct usb_hub *hub, int port1,
                         usb_set_device_state(udev, status
                                         ? USB_STATE_NOTATTACHED
                                         : USB_STATE_DEFAULT);
-                        return status;
+                        goto done;
                 }
 
                 dev_dbg (hub->intfdev,
@@ -1625,6 +1636,8 @@ static int hub_port_reset(struct usb_hub *hub, int port1,
                 "Cannot enable port %i.  Maybe the USB cable is bad?\n",
                 port1);
 
+ done:
+        up_read(&ehci_cf_port_reset_rwsem);
         return status;
 }