USB: automatically enable RHSC interrupts

This patch (as1069c) changes the way OHCI root-hub status-change
interrupts are enabled.  Currently a special HCD method,
hub_irq_enable(), is called when the hub driver is finished using a
root hub.  This approach turns out to be subject to races, resulting
in unnecessary polling.

The patch does away with the method entirely.  Instead, the driver
automatically enables the RHSC interrupt when no more status changes
are present.  This scheme is safe with controllers using
level-triggered semantics for their interrupt flags.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 31 insertions, 22 deletions

diff --git a/drivers/usb/host/ohci-hub.c b/drivers/usb/host/ohci-hub.c
index 439beb784f3e..7ea9a7b31155 100644
--- a/drivers/usb/host/ohci-hub.c
+++ b/drivers/usb/host/ohci-hub.c
@@ -36,18 +36,6 @@
 
 /*-------------------------------------------------------------------------*/
 
-/* hcd->hub_irq_enable() */
-static void ohci_rhsc_enable (struct usb_hcd *hcd)
-{
-        struct ohci_hcd         *ohci = hcd_to_ohci (hcd);
-
-        spin_lock_irq(&ohci->lock);
-        if (!ohci->autostop)
-                del_timer(&hcd->rh_timer);      /* Prevent next poll */
-        ohci_writel(ohci, OHCI_INTR_RHSC, &ohci->regs->intrenable);
-        spin_unlock_irq(&ohci->lock);
-}
-
 #define OHCI_SCHED_ENABLES \
         (OHCI_CTRL_CLE|OHCI_CTRL_BLE|OHCI_CTRL_PLE|OHCI_CTRL_IE)
 
@@ -374,18 +362,28 @@ static int ohci_root_hub_state_changes(struct ohci_hcd *ohci, int changed,
                 int any_connected)
 {
         int     poll_rh = 1;
+        int     rhsc;
 
+        rhsc = ohci_readl(ohci, &ohci->regs->intrenable) & OHCI_INTR_RHSC;
         switch (ohci->hc_control & OHCI_CTRL_HCFS) {
 
         case OHCI_USB_OPER:
-                /* keep on polling until we know a device is connected
-                 * and RHSC is enabled */
+                /* If no status changes are pending, enable status-change
+                 * interrupts.
+                 */
+                if (!rhsc && !changed) {
+                        rhsc = OHCI_INTR_RHSC;
+                        ohci_writel(ohci, rhsc, &ohci->regs->intrenable);
+                }
+
+                /* Keep on polling until we know a device is connected
+                 * and RHSC is enabled, or until we autostop.
+                 */
                 if (!ohci->autostop) {
                         if (any_connected ||
                                         !device_may_wakeup(&ohci_to_hcd(ohci)
                                                 ->self.root_hub->dev)) {
-                                if (ohci_readl(ohci, &ohci->regs->intrenable) &
-                                                OHCI_INTR_RHSC)
+                                if (rhsc)
                                         poll_rh = 0;
                         } else {
                                 ohci->autostop = 1;
@@ -398,12 +396,13 @@ static int ohci_root_hub_state_changes(struct ohci_hcd *ohci, int changed,
                                 ohci->autostop = 0;
                                 ohci->next_statechange = jiffies +
                                                 STATECHANGE_DELAY;
-                        } else if (time_after_eq(jiffies,
+                        } else if (rhsc && time_after_eq(jiffies,
                                                 ohci->next_statechange)
                                         && !ohci->ed_rm_list
                                         && !(ohci->hc_control &
                                                 OHCI_SCHED_ENABLES)) {
                                 ohci_rh_suspend(ohci, 1);
+                                poll_rh = 0;
                         }
                 }
                 break;
@@ -417,6 +416,12 @@ static int ohci_root_hub_state_changes(struct ohci_hcd *ohci, int changed,
                         else
                                 usb_hcd_resume_root_hub(ohci_to_hcd(ohci));
                 } else {
+                        if (!rhsc && (ohci->autostop ||
+                                        ohci_to_hcd(ohci)->self.root_hub->
+                                                do_remote_wakeup))
+                                ohci_writel(ohci, OHCI_INTR_RHSC,
+                                                &ohci->regs->intrenable);
+
                         /* everything is idle, no need for polling */
                         poll_rh = 0;
                 }
@@ -438,12 +443,16 @@ static inline int ohci_rh_resume(struct ohci_hcd *ohci)
 static int ohci_root_hub_state_changes(struct ohci_hcd *ohci, int changed,
                 int any_connected)
 {
-        int     poll_rh = 1;
-
-        /* keep on polling until RHSC is enabled */
+        /* If RHSC is enabled, don't poll */
         if (ohci_readl(ohci, &ohci->regs->intrenable) & OHCI_INTR_RHSC)
-                poll_rh = 0;
-        return poll_rh;
+                return 0;
+
+        /* If no status changes are pending, enable status-change interrupts */
+        if (!changed) {
+                ohci_writel(ohci, OHCI_INTR_RHSC, &ohci->regs->intrenable);
+                return 0;
+        }
+        return 1;
 }
 
 #endif  /* CONFIG_PM */