[x86 setup] APM: BX should be zero when disconnecting

For APM calls, BX contains the device index, which is zero for
the system BIOS.  Disconnect requres BX = 0.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

1 files changed, 3 insertions, 2 deletions

diff --git a/arch/i386/boot/apm.c b/arch/i386/boot/apm.c
index 8be3f5686af6..eab50c55a3a5 100644
--- a/arch/i386/boot/apm.c
+++ b/arch/i386/boot/apm.c
@@ -45,9 +45,10 @@ int query_apm_bios(void)
 
         /* Disconnect first, just in case */
         ax = 0x5304;
+        bx = 0;
         asm volatile("pushl %%ebp ; int $0x15 ; popl %%ebp"
-                     : "+a" (ax)
-                     : : "ebx", "ecx", "edx", "esi", "edi");
+                     : "+a" (ax), "+b" (bx)
+                     : : "ecx", "edx", "esi", "edi");
 
         /* Paranoia */
         ebx = esi = 0;