[Qemu-devel] [PATCH v3] target-arm: Make the counter tick relative to cntfrq

[Andrew Jeffery <andrew@aj.id.au>]

Allow machines to configure CNTFRQ via a property if the ARM core
supports the generic timer. This is necessary on e.g. the ASPEED AST2600
SoC where the generic timer clock is run at 800MHz or above.

CNTFRQ is a read-as-written co-processor register; the property sets the
register's initial value which is used during realize() to configure the
QEMUTimers that back the generic timers. Beyond that the firmware can to
do whatever it sees fit with the CNTFRQ register though changes to the
value will not be reflected in the timers' rate.

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
---
Peter - I think this addresses most of your feedback. I still reach into
the QEMUTimer to fetch out scale when adjusting the nexttick
calculation, but we no longer need to update the scale member and force
a recalculation of the period.
---
 target/arm/cpu.c    | 36 ++++++++++++++++++++++++++++--------
 target/arm/helper.c | 20 +++++++++++++++++---
 2 files changed, 45 insertions(+), 11 deletions(-)

diff --git a/target/arm/cpu.c b/target/arm/cpu.c
index 2399c144718d..7ac422729608 100644
--- a/target/arm/cpu.c
+++ b/target/arm/cpu.c
@@ -40,6 +40,8 @@
 #include "disas/capstone.h"
 #include "fpu/softfloat.h"
 
+#include <inttypes.h>
+
 static void arm_cpu_set_pc(CPUState *cs, vaddr value)
 {
     ARMCPU *cpu = ARM_CPU(cs);
@@ -976,6 +978,10 @@ static void arm_cpu_initfn(Object *obj)
     }
 }
 
+static Property arm_cpu_cp_cntfrq_property =
+            DEFINE_PROP_UINT64("cntfrq", ARMCPU, env.cp15.c14_cntfrq,
+                               (1000 * 1000 * 1000) / GTIMER_SCALE);
+
 static Property arm_cpu_reset_cbar_property =
             DEFINE_PROP_UINT64("reset-cbar", ARMCPU, reset_cbar, 0);
 
@@ -1172,6 +1178,11 @@ void arm_cpu_post_init(Object *obj)
 
     qdev_property_add_static(DEVICE(obj), &arm_cpu_cfgend_property,
                              &error_abort);
+
+    if (arm_feature(&cpu->env, ARM_FEATURE_GENERIC_TIMER)) {
+        qdev_property_add_static(DEVICE(cpu), &arm_cpu_cp_cntfrq_property,
+                                 &error_abort);
+    }
 }
 
 static void arm_cpu_finalizefn(Object *obj)
@@ -1238,14 +1249,23 @@ static void arm_cpu_realizefn(DeviceState *dev, Error **errp)
         }
     }
 
-    cpu->gt_timer[GTIMER_PHYS] = timer_new(QEMU_CLOCK_VIRTUAL, GTIMER_SCALE,
-                                           arm_gt_ptimer_cb, cpu);
-    cpu->gt_timer[GTIMER_VIRT] = timer_new(QEMU_CLOCK_VIRTUAL, GTIMER_SCALE,
-                                           arm_gt_vtimer_cb, cpu);
-    cpu->gt_timer[GTIMER_HYP] = timer_new(QEMU_CLOCK_VIRTUAL, GTIMER_SCALE,
-                                          arm_gt_htimer_cb, cpu);
-    cpu->gt_timer[GTIMER_SEC] = timer_new(QEMU_CLOCK_VIRTUAL, GTIMER_SCALE,
-                                          arm_gt_stimer_cb, cpu);
+    if (!env->cp15.c14_cntfrq) {
+        error_setg(errp, "Invalid CNTFRQ: %"PRIx64"Hz", env->cp15.c14_cntfrq);
+        return;
+    }
+
+    {
+        uint64_t scale = MAX(1, NANOSECONDS_PER_SECOND / env->cp15.c14_cntfrq);
+
+        cpu->gt_timer[GTIMER_PHYS] = timer_new(QEMU_CLOCK_VIRTUAL, scale,
+                                               arm_gt_ptimer_cb, cpu);
+        cpu->gt_timer[GTIMER_VIRT] = timer_new(QEMU_CLOCK_VIRTUAL, scale,
+                                               arm_gt_vtimer_cb, cpu);
+        cpu->gt_timer[GTIMER_HYP] = timer_new(QEMU_CLOCK_VIRTUAL, scale,
+                                              arm_gt_htimer_cb, cpu);
+        cpu->gt_timer[GTIMER_SEC] = timer_new(QEMU_CLOCK_VIRTUAL, scale,
+                                              arm_gt_stimer_cb, cpu);
+    }
 #endif
 
     cpu_exec_realizefn(cs, &local_err);
diff --git a/target/arm/helper.c b/target/arm/helper.c
index 507026c9154b..8783f92c718c 100644
--- a/target/arm/helper.c
+++ b/target/arm/helper.c
@@ -2409,7 +2409,21 @@ static CPAccessResult gt_stimer_access(CPUARMState *env,
 
 static uint64_t gt_get_countervalue(CPUARMState *env)
 {
-    return qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) / GTIMER_SCALE;
+    uint64_t effective;
+
+    /*
+     * Deal with quantized clock scaling by calculating the effective frequency
+     * in terms of the timer scale.
+     */
+    if (env->cp15.c14_cntfrq <= NANOSECONDS_PER_SECOND) {
+        uint32_t scale = NANOSECONDS_PER_SECOND / env->cp15.c14_cntfrq;
+        effective = NANOSECONDS_PER_SECOND / scale;
+    } else {
+        effective = NANOSECONDS_PER_SECOND;
+    }
+
+    return muldiv64(qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL), effective,
+                    NANOSECONDS_PER_SECOND);
 }
 
 static void gt_recalc_timer(ARMCPU *cpu, int timeridx)
@@ -2445,8 +2459,8 @@ static void gt_recalc_timer(ARMCPU *cpu, int timeridx)
          * set the timer for as far in the future as possible. When the
          * timer expires we will reset the timer for any remaining period.
          */
-        if (nexttick > INT64_MAX / GTIMER_SCALE) {
-            nexttick = INT64_MAX / GTIMER_SCALE;
+        if (nexttick > INT64_MAX / cpu->gt_timer[timeridx]->scale) {
+            nexttick = INT64_MAX / cpu->gt_timer[timeridx]->scale;
         }
         timer_mod(cpu->gt_timer[timeridx], nexttick);
         trace_arm_gt_recalc(timeridx, irqstate, nexttick);
-- 
2.20.1