b43: avoid PPC fault during resume

The routine b43_is_hw_radio_enabled() has long been a problem.
For PPC architecture with PHY Revision < 3, a read of the register
B43_MMIO_HWENABLED_LO will cause a CPU fault unless b43_status()
returns a value of 2 (B43_STAT_STARTED) (BUG 14181). Fixing that
results in Bug 14538 in which the driver is unable to reassociate
after resuming from hibernation because b43_status() returns 0.

The correct fix would be to determine why the status is 0; however,
I have not yet found why that happens. The correct value is found for
my device, which has PHY revision >= 3.

Returning TRUE when the PHY revision < 3 and b43_status() returns 0 fixes
the regression for 2.6.32.

This patch fixes the problem in Red Hat Bugzilla #538523.
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Tested-by: Christian Casteyde <casteyde.christian@free.fr>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/b43/rfkill.c

@@ -33,8 +33,14 @@ bool b43_is_hw_radio_enabled(struct b43_wldev *dev)
 		      & B43_MMIO_RADIO_HWENABLED_HI_MASK))
 			return 1;
 	} else {
-		if (b43_status(dev) >= B43_STAT_STARTED &&
-		    b43_read16(dev, B43_MMIO_RADIO_HWENABLED_LO)
+		/* To prevent CPU fault on PPC, do not read a register
+		 * unless the interface is started; however, on resume
+		 * for hibernation, this routine is entered early. When
+		 * that happens, unconditionally return TRUE.
+		 */
+		if (b43_status(dev) < B43_STAT_STARTED)
+			return 1;
+		if (b43_read16(dev, B43_MMIO_RADIO_HWENABLED_LO)
 		    & B43_MMIO_RADIO_HWENABLED_LO_MASK)
 			return 1;
 	}