x86: provide delay loop for x86_64.

This is for consistency with i386. We call use_tsc_delay()
at tsc initialization for x86_64, so we'll be always using it.

Signed-off-by: Glauber Costa <gcosta@redhat.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 41 insertions, 4 deletions

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 3c36f92160c9..4a775d001957 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -513,6 +513,7 @@ void __init tsc_init(void)
          */
         for_each_possible_cpu(cpu)
                 set_cyc2ns_scale(cpu_khz, cpu);
+        use_tsc_delay();
 
         if (tsc_disabled > 0)
                 return;
diff --git a/arch/x86/lib/delay_64.c b/arch/x86/lib/delay_64.c
index 4c441be92641..d0326d07c845 100644
--- a/arch/x86/lib/delay_64.c
+++ b/arch/x86/lib/delay_64.c
@@ -22,13 +22,28 @@
 #include <asm/smp.h>
 #endif
 
-int __devinit read_current_timer(unsigned long *timer_value)
+/* simple loop based delay: */
+static void delay_loop(unsigned long loops)
 {
-        rdtscll(*timer_value);
-        return 0;
+        asm volatile(
+                "       test %0,%0      \n"
+                "       jz 3f           \n"
+                "       jmp 1f          \n"
+
+                ".align 16              \n"
+                "1:     jmp 2f          \n"
+
+                ".align 16              \n"
+                "2:     dec %0          \n"
+                "       jnz 2b          \n"
+                "3:     dec %0          \n"
+
+                : /* we don't need output */
+                :"a" (loops)
+        );
 }
 
-void __delay(unsigned long loops)
+static void delay_tsc(unsigned long loops)
 {
         unsigned bclock, now;
         int cpu;
@@ -63,6 +78,27 @@ void __delay(unsigned long loops)
         }
         preempt_enable();
 }
+
+static void (*delay_fn)(unsigned long) = delay_loop;
+
+void use_tsc_delay(void)
+{
+        delay_fn = delay_tsc;
+}
+
+int __devinit read_current_timer(unsigned long *timer_value)
+{
+        if (delay_fn == delay_tsc) {
+                rdtscll(*timer_value);
+                return 0;
+        }
+        return -1;
+}
+
+void __delay(unsigned long loops)
+{
+        delay_fn(loops);
+}
 EXPORT_SYMBOL(__delay);
 
 inline void __const_udelay(unsigned long xloops)