From c0379aec241c78fe07074fa7e63a5009a4e7944a Mon Sep 17 00:00:00 2001
From: Brian Brooks <brian.brooks@arm.com>
Date: Tue, 9 Jan 2018 16:39:07 -0600
Subject: Arm system counter cleanup

Add some description and cleanup code that uses Arm system counter.

Change-Id: Ie1fe00e3e4b5d98867617b7b0184ac526e333c53
Signed-off-by: Brian Brooks <brian.brooks@arm.com>
---
 src/vppinfra/time.c | 15 +++++++++------
 src/vppinfra/time.h | 22 ++++++++++------------
 2 files changed, 19 insertions(+), 18 deletions(-)

(limited to 'src/vppinfra')

diff --git a/src/vppinfra/time.c b/src/vppinfra/time.c
index 770ed8b6807..1626ff4ed38 100644
--- a/src/vppinfra/time.c
+++ b/src/vppinfra/time.c
@@ -142,17 +142,20 @@ done:
 f64
 os_cpu_clock_frequency (void)
 {
+#if defined (__aarch64__)
+  /* The system counter increments at a fixed frequency. It is distributed
+   * to each core which has registers for reading the current counter value
+   * as well as the clock frequency. The system counter is not clocked at
+   * the same frequency as the core. */
+  u32 hz;
+  asm volatile ("mrs %0, cntfrq_el0":"=r" (hz));
+  return (f64) hz;
+#endif
   f64 cpu_freq;
 
   if (clib_cpu_supports_invariant_tsc ())
     return estimate_clock_frequency (1e-3);
 
-#if defined (__aarch64__)
-  u64 tsc;
-  asm volatile ("mrs %0, CNTFRQ_EL0":"=r" (tsc));
-  return (f64) tsc;
-#endif
-
   /* First try /sys version. */
   cpu_freq = clock_frequency_from_sys_filesystem ();
   if (cpu_freq != 0)
diff --git a/src/vppinfra/time.h b/src/vppinfra/time.h
index 288922d8a83..ead4b7d8ea4 100644
--- a/src/vppinfra/time.h
+++ b/src/vppinfra/time.h
@@ -114,6 +114,16 @@ clib_cpu_time_now (void)
   return (u64) lo + ((u64) hi2 << (u64) 32);
 }
 
+#elif defined (__aarch64__)
+always_inline u64
+clib_cpu_time_now (void)
+{
+  u64 vct;
+  /* User access to cntvct_el0 is enabled in Linux kernel since 3.12. */
+  asm volatile ("mrs %0, cntvct_el0":"=r" (vct));
+  return vct;
+}
+
 #elif defined (__arm__)
 #if defined(__ARM_ARCH_8A__)
 always_inline u64
@@ -164,18 +174,6 @@ clib_cpu_time_now (void)
   return ((u64) h << 32) | l;
 }
 
-#elif defined (__aarch64__)
-always_inline u64
-clib_cpu_time_now (void)
-{
-  u64 tsc;
-
-  /* Works on Cavium ThunderX. Other platforms: YMMV */
-  asm volatile ("mrs %0, cntvct_el0":"=r" (tsc));
-
-  return tsc;
-}
-
 #else
 #error "don't know how to read CPU time stamp"
 
-- 
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