[PATCH] Fix infinite loop in grub_pit_wait()

[Christian Franke <Christian.Franke@t-online.de>]

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grub2 from current SVN hangs if run in VirtualPC, the problem was 
introduced with 'svn diff -r 1779:1780'.

Here is a proposed fix.

Christian

2008-08-07  Christian Franke  <franke@computer.org>

	* kern/i386/pit.c (TIMER2_SPEAKER): New define.
	(TIMER2_GATE): Likewise.
	(grub_pit_wait): Add enable/disable of the timer2 gate
	bit of port 0x61. This fixes a possible infinite loop.



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diff --git a/kern/i386/pit.c b/kern/i386/pit.c
index d0a6eda..a3fab26 100644
--- a/kern/i386/pit.c
+++ b/kern/i386/pit.c
@@ -28,13 +28,26 @@
 #define TIMER_ENABLE_LSB	0x20
 #define TIMER_ENABLE_MSB	0x10
 #define TIMER2_LATCH		0x20
+#define TIMER2_SPEAKER		0x02
+#define TIMER2_GATE		0x01
 
 void
 grub_pit_wait (grub_uint16_t tics)
 {
+  /* Disable timer2 gate and speaker.  */
+  grub_outb (grub_inb (TIMER2_REG_LATCH) & ~ (TIMER2_SPEAKER | TIMER2_GATE), TIMER2_REG_LATCH);
+
+  /* Set tics.  */
   grub_outb (TIMER2_SELECT | TIMER_ENABLE_LSB | TIMER_ENABLE_MSB, TIMER_REG_COMMAND);
   grub_outb (tics & 0xff, TIMER2_REG_CONTROL);
   grub_outb (tics >> 8, TIMER2_REG_CONTROL);
 
+  /* Enable timer2 gate, keep speaker disabled.  */
+  grub_outb ((grub_inb (TIMER2_REG_LATCH) & ~ TIMER2_SPEAKER) | TIMER2_GATE, TIMER2_REG_LATCH);
+
+  /* Wait.  */
   while ((grub_inb (TIMER2_REG_LATCH) & TIMER2_LATCH) == 0x00);
+
+  /* Disable timer2 gate and speaker.  */
+  grub_outb (grub_inb (TIMER2_REG_LATCH) & ~ (TIMER2_SPEAKER | TIMER2_GATE), TIMER2_REG_LATCH);
 }