[IA64] allow user to force_pal_cache_flush

The sequence executed in check_sal_cache_flush:

	- pend a timer interrupt
	- call SAL_CACHE_FLUSH
	- see if interrupt is still pending

can hang HP machines with buggy SAL_CACHE_FLUSH implementations.

Provide a kernel command-line argument to allow users skip this
check if desired. Using this parameter will force ia64_sal_cache_flush
to call ia64_pal_cache_flush() instead of SAL_CACHE_FLUSH.
Signed-off-by: Alex Chiang <achiang@hp.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>

Documentation/kernel-parameters.txt

@@ -689,6 +689,12 @@ and is between 256 and 4096 characters. It is defined in the file
 	floppy=		[HW]
 			See Documentation/floppy.txt.
 
+	force_pal_cache_flush
+			[IA-64] Avoid check_sal_cache_flush which may hang on
+			buggy SAL_CACHE_FLUSH implementations. Using this
+			parameter will force ia64_sal_cache_flush to call
+			ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
+
 	gamecon.map[2|3]=
 			[HW,JOY] Multisystem joystick and NES/SNES/PSX pad
 			support via parallel port (up to 5 devices per port)

arch/ia64/kernel/sal.c

@@ -229,6 +229,14 @@ static void __init sal_desc_ap_wakeup(void *p) { }
  */
 static int sal_cache_flush_drops_interrupts;
 
+static int __init
+force_pal_cache_flush(char *str)
+{
+	sal_cache_flush_drops_interrupts = 1;
+	return 0;
+}
+early_param("force_pal_cache_flush", force_pal_cache_flush);
+
 void __init
 check_sal_cache_flush (void)
 {
@@ -237,6 +245,9 @@ check_sal_cache_flush (void)
 	u64 vector, cache_type = 3;
 	struct ia64_sal_retval isrv;
 
+	if (sal_cache_flush_drops_interrupts)
+		return;
+
 	cpu = get_cpu();
 	local_irq_save(flags);