[U-Boot] [PATCH] x86: tsc: add support for reading CPU freq from cpuid

[Christian Gmeiner]

Starting with cpuid level 0x16 (Skylake-based processors)
it is possible to get CPU base freq via cpuid.

This fixes booting on a skylake based system.

Signed-off-by: Christian Gmeiner <christian.gmeiner at gmail.com>
---
 drivers/timer/tsc_timer.c | 31 +++++++++++++++++++++++++------
 1 file changed, 25 insertions(+), 6 deletions(-)

diff --git a/drivers/timer/tsc_timer.c b/drivers/timer/tsc_timer.c
index c7fefd2031..96a3e55513 100644
--- a/drivers/timer/tsc_timer.c
+++ b/drivers/timer/tsc_timer.c
@@ -21,6 +21,17 @@
 
 DECLARE_GLOBAL_DATA_PTR;
 
+static unsigned long cpu_mhz_from_cpuid(void)
+{
+	if (gd->arch.x86_vendor != X86_VENDOR_INTEL)
+		return 0;
+
+	if (cpuid_eax(0) < 0x16)
+		return 0;
+
+	return cpuid_eax(0x16);
+}
+
 /*
  * According to Intel 64 and IA-32 System Programming Guide,
  * if MSR_PERF_STAT[31] is set, the maximum resolved bus ratio can be
@@ -343,14 +354,22 @@ static void tsc_timer_ensure_setup(void)
 	if (!gd->arch.clock_rate) {
 		unsigned long fast_calibrate;
 
+		fast_calibrate = cpu_mhz_from_cpuid();
+		if (fast_calibrate)
+			goto done;
+
 		fast_calibrate = cpu_mhz_from_msr();
-		if (!fast_calibrate) {
-			fast_calibrate = quick_pit_calibrate();
-			if (!fast_calibrate)
-				panic("TSC frequency is ZERO");
-		}
+		if (fast_calibrate)
+			goto done;
+
+		fast_calibrate = quick_pit_calibrate();
+		if (fast_calibrate)
+			goto done;
+
+		panic("TSC frequency is ZERO");
 
-		gd->arch.clock_rate = fast_calibrate * 1000000;
+		done:
+			gd->arch.clock_rate = fast_calibrate * 1000000;
 	}
 }
 
-- 
2.17.0