If we copy the code from the manual, we might as well copy the comments.
Okay?
Index: arch/amd64/amd64/locore.S
===================================================================
RCS file: /cvs/src/sys/arch/amd64/amd64/locore.S,v
retrieving revision 1.52
diff -u -p -r1.52 locore.S
--- arch/amd64/amd64/locore.S 6 May 2012 04:20:40 -0000 1.52
+++ arch/amd64/amd64/locore.S 18 Sep 2012 21:09:12 -0000
@@ -1060,29 +1060,42 @@ ENTRY(pagezero)
#if NACPI > 0
ENTRY(acpi_acquire_global_lock)
- movq %rdi, %rcx
-1: movl (%rcx), %eax
+ movq %rdi, %rcx /* ecx = Address of Global Lock in FACS */
+1: movl (%rcx), %eax /* Get current value of Global Lock */
+
movl %eax, %edx
- andl $~1, %edx
- btsl $1, %edx
- adcl $0, %edx
+ andl $~1, %edx /* Clear pending bit */
+ btsl $1, %edx /* Check and set owner bit */
+ adcl $0, %edx /* If owned set pending bit */
+
lock
- cmpxchgl %edx, (%rcx)
- jnz 1b
- andl $3, %edx
+ cmpxchgl %edx, (%rcx) /* Attempt to set new value */
+ jnz 1b /* If not set, try again */
+
+ andl $3, %edx /* Was it acquired or marked pending? */
cmpl $3, %edx
- sbb %eax, %eax
+ sbb %eax, %eax /* acquired = -1, pending = 0 */
+
ret
ENTRY(acpi_release_global_lock)
- movq %rdi, %rcx
-1: movl (%rcx), %eax
+ movq %rdi, %rcx /* ecx = Address of Global Lock in FACS */
+1: movl (%rcx), %eax /* Get current value of Global Lock */
+
movl %eax, %edx
- andl $~3, %edx
+ andl $~3, %edx /* Clear owner and pending field */
+
lock
- cmpxchgl %edx, (%rcx)
- jnz 1b
- andl $1, %eax
+ cmpxchgl %edx, (%rcx) /* Attempt to set it */
+ jnz 1b /* If not set, try again */
+
+ andl $1, %eax /* Was pending set? */
+
+ /*
+ * If one is returned (we were pending) the caller must signal that the
+ * lock has been released using either GBL_RLS or BIOS_RLS as
+ * appropriate.
+ */
ret
#endif
Index: arch/i386/i386/locore.s
===================================================================
RCS file: /cvs/src/sys/arch/i386/i386/locore.s,v
retrieving revision 1.141
diff -u -p -r1.141 locore.s
--- arch/i386/i386/locore.s 2 Nov 2011 23:53:44 -0000 1.141
+++ arch/i386/i386/locore.s 18 Sep 2012 21:09:13 -0000
@@ -1653,29 +1653,42 @@ ENTRY(i686_pagezero)
#if NACPI > 0
ENTRY(acpi_acquire_global_lock)
- movl 4(%esp), %ecx
-1: movl (%ecx), %eax
+ movl 4(%esp), %ecx /* ecx = Address of Global Lock in FACS */
+1: movl (%ecx), %eax /* Get current value of Global Lock */
+
movl %eax, %edx
- andl $~1, %edx
- btsl $1, %edx
- adcl $0, %edx
+ andl $~1, %edx /* Clear pending bit */
+ btsl $1, %edx /* Check and set owner bit */
+ adcl $0, %edx /* If owned set pending bit */
+
lock
- cmpxchgl %edx, (%ecx)
- jnz 1b
- andl $3, %edx
+ cmpxchgl %edx, (%ecx) /* Attempt to set new value */
+ jnz 1b /* If not set, try again */
+
+ andl $3, %edx /* Was it acquired or marked pending? */
cmpl $3, %edx
- sbb %eax, %eax
+ sbb %eax, %eax /* acquired = -1, pending = 0 */
+
ret
ENTRY(acpi_release_global_lock)
- movl 4(%esp), %ecx
-1: movl (%ecx), %eax
+ movl 4(%esp), %ecx /* ecx = Address of Global Lock in FACS */
+1: movl (%ecx), %eax /* Get current value of Global Lock */
+
movl %eax, %edx
- andl $~3, %edx
+ andl $~3, %edx /* Clear owner and pending field */
+
lock
- cmpxchgl %edx, (%ecx)
- jnz 1b
- andl $1, %eax
+ cmpxchgl %edx, (%ecx) /* Attempt to set it */
+ jnz 1b /* If not set, try again */
+
+ andl $1, %eax /* Was pending set? */
+
+ /*
+ * If one is returned (we were pending) the caller must signal that the
+ * lock has been released using either GBL_RLS or BIOS_RLS as
+ * appropriate.
+ */
ret
#endif
