USB: convert usb_hcd bitfields into atomic flags

This patch (as1393) converts several of the single-bit fields in
struct usb_hcd to atomic flags.  This is for safety's sake; not all
CPUs can update bitfield values atomically, and these flags are used
in multiple contexts.

The flag fields that are set only during registration or removal can
remain as they are, since non-atomic accesses at those times will not
cause any problems.

(Strictly speaking, the authorized_default flag should become atomic
as well.  I didn't bother with it because it gets changed only via
sysfs.  It can be done later, if anyone wants.)

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

1 files changed, 17 insertions, 5 deletions

diff --git a/include/linux/usb/hcd.h b/include/linux/usb/hcd.h
index 9b867e64a0f4..f8f8fa7a56e8 100644
--- a/include/linux/usb/hcd.h
+++ b/include/linux/usb/hcd.h
@@ -89,19 +89,31 @@ struct usb_hcd {
          */
         const struct hc_driver  *driver;        /* hw-specific hooks */
 
-        /* Flags that need to be manipulated atomically */
+        /* Flags that need to be manipulated atomically because they can
+         * change while the host controller is running.  Always use
+         * set_bit() or clear_bit() to change their values.
+         */
         unsigned long           flags;
-#define HCD_FLAG_HW_ACCESSIBLE  0x00000001
-#define HCD_FLAG_SAW_IRQ        0x00000002
+#define HCD_FLAG_HW_ACCESSIBLE          0       /* at full power */
+#define HCD_FLAG_SAW_IRQ                1
+#define HCD_FLAG_POLL_RH                2       /* poll for rh status? */
+#define HCD_FLAG_POLL_PENDING           3       /* status has changed? */
+
+        /* The flags can be tested using these macros; they are likely to
+         * be slightly faster than test_bit().
+         */
+#define HCD_HW_ACCESSIBLE(hcd)  ((hcd)->flags & (1U << HCD_FLAG_HW_ACCESSIBLE))
+#define HCD_SAW_IRQ(hcd)        ((hcd)->flags & (1U << HCD_FLAG_SAW_IRQ))
+#define HCD_POLL_RH(hcd)        ((hcd)->flags & (1U << HCD_FLAG_POLL_RH))
+#define HCD_POLL_PENDING(hcd)   ((hcd)->flags & (1U << HCD_FLAG_POLL_PENDING))
 
+        /* Flags that get set only during HCD registration or removal. */
         unsigned                rh_registered:1;/* is root hub registered? */
         unsigned                rh_pollable:1;  /* may we poll the root hub? */
 
         /* The next flag is a stopgap, to be removed when all the HCDs
          * support the new root-hub polling mechanism. */
         unsigned                uses_new_polling:1;
-        unsigned                poll_rh:1;      /* poll for rh status? */
-        unsigned                poll_pending:1; /* status has changed? */
         unsigned                wireless:1;     /* Wireless USB HCD */
         unsigned                authorized_default:1;
         unsigned                has_tt:1;       /* Integrated TT in root hub */