--- zzzz-none-000/linux-3.10.107/arch/x86/lib/delay.c	2017-06-27 09:49:32.000000000 +0000
+++ scorpion-7490-727/linux-3.10.107/arch/x86/lib/delay.c	2021-02-04 17:41:59.000000000 +0000
@@ -16,11 +16,11 @@
 #include <linux/timex.h>
 #include <linux/preempt.h>
 #include <linux/delay.h>
-#include <linux/init.h>
 
 #include <asm/processor.h>
 #include <asm/delay.h>
 #include <asm/timer.h>
+#include <asm/mwait.h>
 
 #ifdef CONFIG_SMP
 # include <asm/smp.h>
@@ -50,16 +50,14 @@
 /* TSC based delay: */
 static void delay_tsc(unsigned long __loops)
 {
-	u32 bclock, now, loops = __loops;
+	u64 bclock, now, loops = __loops;
 	int cpu;
 
 	preempt_disable();
 	cpu = smp_processor_id();
-	rdtsc_barrier();
-	rdtscl(bclock);
+	bclock = rdtsc_ordered();
 	for (;;) {
-		rdtsc_barrier();
-		rdtscl(now);
+		now = rdtsc_ordered();
 		if ((now - bclock) >= loops)
 			break;
 
@@ -80,14 +78,51 @@
 		if (unlikely(cpu != smp_processor_id())) {
 			loops -= (now - bclock);
 			cpu = smp_processor_id();
-			rdtsc_barrier();
-			rdtscl(bclock);
+			bclock = rdtsc_ordered();
 		}
 	}
 	preempt_enable();
 }
 
 /*
+ * On some AMD platforms, MWAITX has a configurable 32-bit timer, that
+ * counts with TSC frequency. The input value is the loop of the
+ * counter, it will exit when the timer expires.
+ */
+static void delay_mwaitx(unsigned long __loops)
+{
+	u64 start, end, delay, loops = __loops;
+
+	start = rdtsc_ordered();
+
+	for (;;) {
+		delay = min_t(u64, MWAITX_MAX_LOOPS, loops);
+
+		/*
+		 * Use cpu_tss as a cacheline-aligned, seldomly
+		 * accessed per-cpu variable as the monitor target.
+		 */
+		__monitorx(this_cpu_ptr(&cpu_tss), 0, 0);
+
+		/*
+		 * AMD, like Intel, supports the EAX hint and EAX=0xf
+		 * means, do not enter any deep C-state and we use it
+		 * here in delay() to minimize wakeup latency.
+		 */
+		__mwaitx(MWAITX_DISABLE_CSTATES, delay, MWAITX_ECX_TIMER_ENABLE);
+
+		end = rdtsc_ordered();
+
+		if (loops <= end - start)
+			break;
+
+		loops -= end - start;
+
+		start = end;
+	}
+}
+
+/*
  * Since we calibrate only once at boot, this
  * function should be set once at boot and not changed
  */
@@ -95,13 +130,19 @@
 
 void use_tsc_delay(void)
 {
-	delay_fn = delay_tsc;
+	if (delay_fn == delay_loop)
+		delay_fn = delay_tsc;
+}
+
+void use_mwaitx_delay(void)
+{
+	delay_fn = delay_mwaitx;
 }
 
 int read_current_timer(unsigned long *timer_val)
 {
 	if (delay_fn == delay_tsc) {
-		rdtscll(*timer_val);
+		*timer_val = rdtsc();
 		return 0;
 	}
 	return -1;