[PATCH v2 2/4] target/arm: Abstract the generic timer frequency

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

Prepare for SoCs such as the ASPEED AST2600 whose firmware configures
CNTFRQ to values significantly larger than the static 62.5MHz value
currently derived from GTIMER_SCALE. As the OS potentially derives its
timer periods from the CNTFRQ value the lack of support for running
QEMUTimers at the appropriate rate leads to sticky behaviour in the
guest.

Substitute the GTIMER_SCALE constant with use of a helper to derive the
period from gt_cntfrq stored in struct ARMCPU. Initially set gt_cntfrq
to the frequency associated with GTIMER_SCALE so current behaviour is
maintained.

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
---
 target/arm/cpu.c    |  2 ++
 target/arm/cpu.h    | 10 ++++++++++
 target/arm/helper.c | 10 +++++++---
 3 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/target/arm/cpu.c b/target/arm/cpu.c
index 7a4ac9339bf9..5698a74061bb 100644
--- a/target/arm/cpu.c
+++ b/target/arm/cpu.c
@@ -974,6 +974,8 @@ static void arm_cpu_initfn(Object *obj)
     if (tcg_enabled()) {
         cpu->psci_version = 2; /* TCG implements PSCI 0.2 */
     }
+
+    cpu->gt_cntfrq = NANOSECONDS_PER_SECOND / GTIMER_SCALE;
 }
 
 static Property arm_cpu_reset_cbar_property =
diff --git a/target/arm/cpu.h b/target/arm/cpu.h
index 83a809d4bac4..666c03871fdf 100644
--- a/target/arm/cpu.h
+++ b/target/arm/cpu.h
@@ -932,8 +932,18 @@ struct ARMCPU {
      */
     DECLARE_BITMAP(sve_vq_map, ARM_MAX_VQ);
     DECLARE_BITMAP(sve_vq_init, ARM_MAX_VQ);
+
+    /* Generic timer counter frequency, in Hz */
+    uint64_t gt_cntfrq;
 };
 
+static inline unsigned int gt_cntfrq_period_ns(ARMCPU *cpu)
+{
+    /* XXX: Could include qemu/timer.h to get NANOSECONDS_PER_SECOND? */
+    const unsigned int ns_per_s = 1000 * 1000 * 1000;
+    return ns_per_s > cpu->gt_cntfrq ? ns_per_s / cpu->gt_cntfrq : 1;
+}
+
 void arm_cpu_post_init(Object *obj);
 
 uint64_t arm_cpu_mp_affinity(int idx, uint8_t clustersz);
diff --git a/target/arm/helper.c b/target/arm/helper.c
index 65c4441a3896..2622a9a8d02f 100644
--- a/target/arm/helper.c
+++ b/target/arm/helper.c
@@ -2409,7 +2409,9 @@ 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;
+    ARMCPU *cpu = env_archcpu(env);
+
+    return qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) / gt_cntfrq_period_ns(cpu);
 }
 
 static void gt_recalc_timer(ARMCPU *cpu, int timeridx)
@@ -2445,7 +2447,7 @@ 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) {
+        if (nexttick > INT64_MAX / gt_cntfrq_period_ns(cpu)) {
             timer_mod_ns(cpu->gt_timer[timeridx], INT64_MAX);
         } else {
             timer_mod(cpu->gt_timer[timeridx], nexttick);
@@ -2874,11 +2876,13 @@ static const ARMCPRegInfo generic_timer_cp_reginfo[] = {
 
 static uint64_t gt_virt_cnt_read(CPUARMState *env, const ARMCPRegInfo *ri)
 {
+    ARMCPU *cpu = env_archcpu(env);
+
     /* Currently we have no support for QEMUTimer in linux-user so we
      * can't call gt_get_countervalue(env), instead we directly
      * call the lower level functions.
      */
-    return cpu_get_clock() / GTIMER_SCALE;
+    return cpu_get_clock() / gt_cntfrq_period_ns(cpu);
 }
 
 static const ARMCPRegInfo generic_timer_cp_reginfo[] = {
-- 
2.20.1