USB: EHCI cpufreq fix

EHCI controllers that don't cache enough microframes can get MMF errors
when CPU frequency changes occur between the start and completion of
split interrupt transactions, due to delays in reading main memory
(caused by CPU cache snoop delays).

This patch adds a cpufreq notifier to the EHCI driver that will
inactivate split interrupt transactions during frequency transitions.
It was tested on Intel ICH7 and Serverworks/Broadcom HT1000 EHCI
controllers.

Signed-off-by: Stuart Hayes <stuart_hayes@dell.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 67 insertions, 0 deletions

diff --git a/drivers/usb/host/ehci-hcd.c b/drivers/usb/host/ehci-hcd.c
index 099aff64f53..566badb05b3 100644
--- a/drivers/usb/host/ehci-hcd.c
+++ b/drivers/usb/host/ehci-hcd.c
@@ -273,6 +273,58 @@ static void ehci_work(struct ehci_hcd *ehci);
 
 /*-------------------------------------------------------------------------*/
 
+#ifdef CONFIG_CPU_FREQ
+
+#include <linux/cpufreq.h>
+
+static void ehci_cpufreq_pause (struct ehci_hcd *ehci)
+{
+	unsigned long	flags;
+
+	spin_lock_irqsave(&ehci->lock, flags);
+	if (!ehci->cpufreq_changing++)
+		qh_inactivate_split_intr_qhs(ehci);
+	spin_unlock_irqrestore(&ehci->lock, flags);
+}
+
+static void ehci_cpufreq_unpause (struct ehci_hcd *ehci)
+{
+	unsigned long	flags;
+
+	spin_lock_irqsave(&ehci->lock, flags);
+	if (!--ehci->cpufreq_changing)
+		qh_reactivate_split_intr_qhs(ehci);
+	spin_unlock_irqrestore(&ehci->lock, flags);
+}
+
+/*
+ * ehci_cpufreq_notifier is needed to avoid MMF errors that occur when
+ * EHCI controllers that don't cache many uframes get delayed trying to
+ * read main memory during CPU frequency transitions.  This can cause
+ * split interrupt transactions to not be completed in the required uframe.
+ * This has been observed on the Broadcom/ServerWorks HT1000 controller.
+ */
+static int ehci_cpufreq_notifier(struct notifier_block *nb, unsigned long val,
+				 void *data)
+{
+	struct ehci_hcd *ehci = container_of(nb, struct ehci_hcd,
+					     cpufreq_transition);
+
+	switch (val) {
+	case CPUFREQ_PRECHANGE:
+		ehci_cpufreq_pause(ehci);
+		break;
+	case CPUFREQ_POSTCHANGE:
+		ehci_cpufreq_unpause(ehci);
+		break;
+	}
+	return 0;
+}
+
+#endif
+
+/*-------------------------------------------------------------------------*/
+
 static void ehci_watchdog (unsigned long param)
 {
 	struct ehci_hcd		*ehci = (struct ehci_hcd *) param;
@@ -404,6 +456,10 @@ static void ehci_stop (struct usb_hcd *hcd)
 	ehci_writel(ehci, 0, &ehci->regs->intr_enable);
 	spin_unlock_irq(&ehci->lock);
 
+#ifdef CONFIG_CPU_FREQ
+	cpufreq_unregister_notifier(&ehci->cpufreq_transition,
+				    CPUFREQ_TRANSITION_NOTIFIER);
+#endif
 	/* let companion controllers work when we aren't */
 	ehci_writel(ehci, 0, &ehci->regs->configured_flag);
 
@@ -509,6 +565,17 @@ static int ehci_init(struct usb_hcd *hcd)
 	}
 	ehci->command = temp;
 
+#ifdef CONFIG_CPU_FREQ
+	INIT_LIST_HEAD(&ehci->split_intr_qhs);
+	/*
+	 * If the EHCI controller caches enough uframes, this probably
+	 * isn't needed unless there are so many low/full speed devices
+	 * that the controller's can't cache it all.
+	 */
+	ehci->cpufreq_transition.notifier_call = ehci_cpufreq_notifier;
+	cpufreq_register_notifier(&ehci->cpufreq_transition,
+				  CPUFREQ_TRANSITION_NOTIFIER);
+#endif
 	return 0;
 }