From 9cbd0df60a1efb5e2622a54f40de557133346246 Mon Sep 17 00:00:00 2001
From: hpa <hpa>
Date: Fri, 19 Aug 2005 03:08:45 +0000
Subject: [PATCH] Saner idle call semantics

---
 NEWS                 |  3 +++
 com32/lib/sys/idle.c |  3 +--
 comboot.doc          | 11 +++++++----
 comboot.inc          |  8 ++++++++
 pxelinux.asm         |  2 ++
 5 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/NEWS b/NEWS
index ba4ebbf..ddc61e9 100644
--- a/NEWS
+++ b/NEWS
@@ -16,6 +16,9 @@ Changes in 3.10:
 	* Comments are now recognized even without a space following #.
 	* Fix incorrect handling of mixes of entries with and without
 	  MENU PASSWD.
+	* The idle API call now harmlessly returns failure if it is a
+	  no-op.  That way the caller can decide whether or not to
+	  bother invoking it again.
 
 Changes in 3.09:
 	* gcc4 compilation fix.
diff --git a/com32/lib/sys/idle.c b/com32/lib/sys/idle.c
index df8cc4a..85e857f 100644
--- a/com32/lib/sys/idle.c
+++ b/com32/lib/sys/idle.c
@@ -51,8 +51,7 @@ void syslinux_idle(void)
   if ( do_idle ) {
     __intcall(0x22, &sys_idle, &idle_result);
 
-    if ( idle_result.eflags.l & EFLAGS_CF )
-      do_idle = 0;
+    do_idle = ~idle_result.eflags.l & EFLAGS_CF;
   }
 
   cpu_relax();
diff --git a/comboot.doc b/comboot.doc
index 8680b71..ec521ad 100644
--- a/comboot.doc
+++ b/comboot.doc
@@ -586,10 +586,13 @@ AX=0013h [3.08] Idle loop call
 	the moment, this is a no-op on all derivatives except
 	PXELINUX, where it executes PXE calls to answer ARP queries.
 
-	Note: it's safe to call this API call on previous SYSLINUX
-	versions (2.00 or later); it will just harmlessly fail.  If
-	API call INT 22h, AX=0015h, bit 1 is set, there is no reason
-	(but safe) to call this routine.
+	Starting with version 3.10, this API call harmlessly returns
+	failure (CF=1) if invoked on a platform which does not need
+	idle calls.  Additionally, it's safe to call this API call on
+	previous SYSLINUX versions (2.00 or later); it will just
+	harmlessly fail.  Thus, if this call returns failure (CF=1),
+	it means that there is no technical reason to call this
+	function again, although doing so is of course safe.
 
 
 AX=0014h [3.10] Local boot [PXELINUX, ISOLINUX]
diff --git a/comboot.inc b/comboot.inc
index a065192..90d9e4b 100644
--- a/comboot.inc
+++ b/comboot.inc
@@ -647,11 +647,19 @@ comapi_shuffle:
 ;
 ; INT 22h AX=0013h	Idle call
 ;
+%ifdef HAVE_IDLE
+
 comapi_idle:
 		DO_IDLE
 		clc
 		ret
 
+%else
+
+comapi_idle	equ comapi_err
+
+%endif
+
 ;
 ; INT 22h AX=0014h	Local boot
 ;
diff --git a/pxelinux.asm b/pxelinux.asm
index 13bb79b..a83afd0 100644
--- a/pxelinux.asm
+++ b/pxelinux.asm
@@ -60,6 +60,8 @@ SECTOR_SIZE	equ TFTP_BLOCKSIZE
 ;
 ; This is what we need to do when idle
 ;
+%define HAVE_IDLE 1			; idle is not a noop
+
 %macro	RESET_IDLE 0
 	call reset_idle
 %endmacro
-- 
2.7.4