1 files changed, 28 insertions, 14 deletions

diff --git a/target/arm/cpu.c b/target/arm/cpu.c
index a152def241..fdc3eda318 100644
--- a/target/arm/cpu.c
+++ b/target/arm/cpu.c
@@ -1506,9 +1506,12 @@ static void arm_cpu_initfn(Object *obj)
     }
 }
 
+/*
+ * 0 means "unset, use the default value". That default might vary depending
+ * on the CPU type, and is set in the realize fn.
+ */
 static Property arm_cpu_gt_cntfrq_property =
-            DEFINE_PROP_UINT64("cntfrq", ARMCPU, gt_cntfrq_hz,
-                               NANOSECONDS_PER_SECOND / GTIMER_SCALE);
+            DEFINE_PROP_UINT64("cntfrq", ARMCPU, gt_cntfrq_hz, 0);
 
 static Property arm_cpu_reset_cbar_property =
             DEFINE_PROP_UINT64("reset-cbar", ARMCPU, reset_cbar, 0);
@@ -1954,6 +1957,26 @@ static void arm_cpu_realizefn(DeviceState *dev, Error **errp)
         return;
     }
 
+    if (!cpu->gt_cntfrq_hz) {
+        /*
+         * 0 means "the board didn't set a value, use the default". (We also
+         * get here for the CONFIG_USER_ONLY case.)
+         * ARMv8.6 and later CPUs architecturally must use a 1GHz timer; before
+         * that it was an IMPDEF choice, and QEMU initially picked 62.5MHz,
+         * which gives a 16ns tick period.
+         *
+         * We will use the back-compat value:
+         *  - for QEMU CPU types added before we standardized on 1GHz
+         *  - for versioned machine types with a version of 9.0 or earlier
+         */
+        if (arm_feature(env, ARM_FEATURE_BACKCOMPAT_CNTFRQ) ||
+            cpu->backcompat_cntfrq) {
+            cpu->gt_cntfrq_hz = GTIMER_BACKCOMPAT_HZ;
+        } else {
+            cpu->gt_cntfrq_hz = GTIMER_DEFAULT_HZ;
+        }
+    }
+
 #ifndef CONFIG_USER_ONLY
     /* The NVIC and M-profile CPU are two halves of a single piece of
      * hardware; trying to use one without the other is a command line
@@ -2002,18 +2025,7 @@ static void arm_cpu_realizefn(DeviceState *dev, Error **errp)
     }
 
     {
-        uint64_t scale;
-
-        if (arm_feature(env, ARM_FEATURE_GENERIC_TIMER)) {
-            if (!cpu->gt_cntfrq_hz) {
-                error_setg(errp, "Invalid CNTFRQ: %"PRId64"Hz",
-                           cpu->gt_cntfrq_hz);
-                return;
-            }
-            scale = gt_cntfrq_period_ns(cpu);
-        } else {
-            scale = GTIMER_SCALE;
-        }
+        uint64_t scale = gt_cntfrq_period_ns(cpu);
 
         cpu->gt_timer[GTIMER_PHYS] = timer_new(QEMU_CLOCK_VIRTUAL, scale,
                                                arm_gt_ptimer_cb, cpu);
@@ -2571,6 +2583,8 @@ static Property arm_cpu_properties[] = {
                         mp_affinity, ARM64_AFFINITY_INVALID),
     DEFINE_PROP_INT32("node-id", ARMCPU, node_id, CPU_UNSET_NUMA_NODE_ID),
     DEFINE_PROP_INT32("core-count", ARMCPU, core_count, -1),
+    /* True to default to the backward-compat old CNTFRQ rather than 1Ghz */
+    DEFINE_PROP_BOOL("backcompat-cntfrq", ARMCPU, backcompat_cntfrq, false),
     DEFINE_PROP_END_OF_LIST()
 };