Re: [RFC] b43: Fix regression from Bug #14538

["John W. Linville" <linville@tuxdriver.com>]

On Mon, Nov 23, 2009 at 01:55:06PM -0600, Larry Finger wrote:
> 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.
> 
> Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
> Tested-by: Christian Casteyde <casteyde.christian@free.fr>
> ---
> 
> Index: wireless-testing/drivers/net/wireless/b43/rfkill.c
> ===================================================================
> --- wireless-testing.orig/drivers/net/wireless/b43/rfkill.c
> +++ wireless-testing/drivers/net/wireless/b43/rfkill.c
> @@ -33,9 +33,16 @@ bool b43_is_hw_radio_enabled(struct b43_
>  		      & B43_MMIO_RADIO_HWENABLED_HI_MASK))
>  			return 1;
>  	} else {
> -		if (b43_status(dev) >= B43_STAT_STARTED &&
> -		    b43_read16(dev, B43_MMIO_RADIO_HWENABLED_LO)
> -		    & B43_MMIO_RADIO_HWENABLED_LO_MASK)
> +		/* 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) {
> +			if (b43_read16(dev, B43_MMIO_RADIO_HWENABLED_LO)
> +			    & B43_MMIO_RADIO_HWENABLED_LO_MASK)
> +				return 1;
> +		} else
>  			return 1;
>  	}
>  	return 0;

Maybe just me, but I think this version is easier to read (and especially to see the difference):

diff --git a/drivers/net/wireless/b43/rfkill.c b/drivers/net/wireless/b43/rfkill.c
index ffdce6f..ddc3c93 100644
--- a/drivers/net/wireless/b43/rfkill.c
+++ b/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;
 	}
-- 
John W. Linville		Someday the world will need a hero, and you
linville@tuxdriver.com			might be all we have.  Be ready.