Input: pcspkr - fix PIT lockup on some chipsets

There've been reports [1] about the sysem bell causing a hard
lockup.  My machine was affected as well: any speaker output hung
the machine completely, nothing in the logs, no magic sysrq,
etc., looked like a hardware problem.  Had a closer look on the
issue, and it turned out that the pcspkr module is responsible.
The cause is the bad setup of Timer 2 in the i8253 controller,
which probably hangs the whole PIT controller.

Intel datasheets [2] state that the timer registers are in an
undefined state after reset and they need to be programmed before
enabling the timer. (And enabling without programming the
frequency first doesn't make sense anyway).

I don't know which chipsets are affected (if not all), it also
depends on the BIOS whether it initializes the timer (e.g. to
beep when you start the machine).

The following patch solved the issue on my ICH6 notebook,
couldn't test it with any others, but should be safe to apply.

[1]
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/146151
https://bugs.launchpad.net/ubuntu/+bug/270790
http://ubuntuforums.org/showthread.php?t=227693
http://bugs.gentoo.org/show_bug.cgi?id=222583
https://bugzilla.redhat.com/show_bug.cgi?id=454225

[2]
http://www.intel.com/assets/pdf/datasheet/252516.pdf
http://www.intel.com/assets/pdf/datasheet/301473.pdf
http://www.intel.com/design/chipsets/datashts/29065503.pdf

Signed-off-by: Zoltan Devai <zdevai@gmail.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

1 files changed, 2 insertions, 2 deletions

diff --git a/drivers/input/misc/pcspkr.c b/drivers/input/misc/pcspkr.c
index 43aaa5cebd12..d6a30cee7bc7 100644
--- a/drivers/input/misc/pcspkr.c
+++ b/drivers/input/misc/pcspkr.c
@@ -52,13 +52,13 @@ static int pcspkr_event(struct input_dev *dev, unsigned int type, unsigned int c
 	spin_lock_irqsave(&i8253_lock, flags);
 
 	if (count) {
-		/* enable counter 2 */
-		outb_p(inb_p(0x61) | 3, 0x61);
 		/* set command for counter 2, 2 byte write */
 		outb_p(0xB6, 0x43);
 		/* select desired HZ */
 		outb_p(count & 0xff, 0x42);
 		outb((count >> 8) & 0xff, 0x42);
+		/* enable counter 2 */
+		outb_p(inb_p(0x61) | 3, 0x61);
 	} else {
 		/* disable counter 2 */
 		outb(inb_p(0x61) & 0xFC, 0x61);