[PATCH v5 03/10] target/ppc: enable PMU counter overflow with cycle events

[Daniel Henrique Barboza <danielhb413@gmail.com>]

The PowerISA v3.1 defines that if the proper bits are set (MMCR0_PMC1CE
for PMC1 and MMCR0_PMCjCE for the remaining PMCs), counter negative
conditions are enabled. This means that if the counter value overflows
(i.e. exceeds 0x80000000) a performance monitor alert will occur. This alert
can trigger an event-based exception (to be implemented in the next patches)
if the MMCR0_EBE bit is set.

For now, overflowing the counter when the PMC is counting cycles will
just trigger a performance monitor alert. This is done by starting the
overflow timer to expire in the moment the overflow would be occuring. The
timer will call fire_PMC_interrupt() (via cpu_ppc_pmu_timer_cb) which will
trigger the PMU alert and, if the conditions are met, an EBB exception.

Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
---
 target/ppc/cpu.h        |  2 +
 target/ppc/power8-pmu.c | 86 ++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 86 insertions(+), 2 deletions(-)

diff --git a/target/ppc/cpu.h b/target/ppc/cpu.h
index 6c4643044b..bf718334a5 100644
--- a/target/ppc/cpu.h
+++ b/target/ppc/cpu.h
@@ -363,6 +363,8 @@ typedef enum {
 #define MMCR0_PMCC   PPC_BITMASK(44, 45) /* PMC Control */
 #define MMCR0_FC14   PPC_BIT(58)         /* PMC Freeze Counters 1-4 bit */
 #define MMCR0_FC56   PPC_BIT(59)         /* PMC Freeze Counters 5-6 bit */
+#define MMCR0_PMC1CE PPC_BIT(48)         /* MMCR0 PMC1 Condition Enabled */
+#define MMCR0_PMCjCE PPC_BIT(49)         /* MMCR0 PMCj Condition Enabled */
 /* MMCR0 userspace r/w mask */
 #define MMCR0_UREG_MASK (MMCR0_FC | MMCR0_PMAO | MMCR0_PMAE)
 /* MMCR2 userspace r/w mask */
diff --git a/target/ppc/power8-pmu.c b/target/ppc/power8-pmu.c
index a0a42b666c..fdc94d40b2 100644
--- a/target/ppc/power8-pmu.c
+++ b/target/ppc/power8-pmu.c
@@ -23,6 +23,8 @@
 
 #if defined(TARGET_PPC64) && !defined(CONFIG_USER_ONLY)
 
+#define COUNTER_NEGATIVE_VAL 0x80000000
+
 /*
  * For PMCs 1-4, IBM POWER chips has support for an implementation
  * dependent event, 0x1E, that enables cycle counting. The Linux kernel
@@ -93,6 +95,15 @@ static bool pmc_is_active(CPUPPCState *env, int sprn)
     return !(env->spr[SPR_POWER_MMCR0] & MMCR0_FC56);
 }
 
+static bool pmc_has_overflow_enabled(CPUPPCState *env, int sprn)
+{
+    if (sprn == SPR_POWER_PMC1) {
+        return env->spr[SPR_POWER_MMCR0] & MMCR0_PMC1CE;
+    }
+
+    return env->spr[SPR_POWER_MMCR0] & MMCR0_PMCjCE;
+}
+
 static void pmu_update_cycles(CPUPPCState *env)
 {
     uint64_t now = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
@@ -121,6 +132,63 @@ static void pmu_update_cycles(CPUPPCState *env)
     }
 }
 
+static void pmu_delete_timers(CPUPPCState *env)
+{
+    int i;
+
+    for (i = 0; i < PMU_TIMERS_NUM; i++) {
+        timer_del(env->pmu_cyc_overflow_timers[i]);
+    }
+}
+
+/*
+ * Helper function to retrieve the cycle overflow timer of the
+ * 'sprn' counter. Given that PMC5 doesn't have a timer, the
+ * amount of timers is less than the total counters and the PMC6
+ * timer is the last of the array.
+ */
+static QEMUTimer *get_cyc_overflow_timer(CPUPPCState *env, int sprn)
+{
+    if (sprn == SPR_POWER_PMC5) {
+        return NULL;
+    }
+
+    if (sprn == SPR_POWER_PMC6) {
+        return env->pmu_cyc_overflow_timers[PMU_TIMERS_NUM - 1];
+    }
+
+    return env->pmu_cyc_overflow_timers[sprn - SPR_POWER_PMC1];
+}
+
+static void pmu_start_overflow_timers(CPUPPCState *env)
+{
+    uint64_t now = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
+    int64_t timeout;
+    int sprn;
+
+    env->pmu_base_time = now;
+
+    /*
+     * Scroll through all PMCs ad start counter overflow timers for
+     * PM_CYC events, if needed.
+     */
+    for (sprn = SPR_POWER_PMC1; sprn <= SPR_POWER_PMC6; sprn++) {
+        if (!pmc_is_active(env, sprn) ||
+            !(getPMUEventType(env, sprn) == PMU_EVENT_CYCLES) ||
+            !pmc_has_overflow_enabled(env, sprn)) {
+            continue;
+        }
+
+        if (env->spr[sprn] >= COUNTER_NEGATIVE_VAL) {
+            timeout =  0;
+        } else {
+            timeout  = COUNTER_NEGATIVE_VAL - env->spr[sprn];
+        }
+
+        timer_mod(get_cyc_overflow_timer(env, sprn), now + timeout);
+    }
+}
+
 /*
  * A cycle count session consists of the basic operations we
  * need to do to support PM_CYC events: redefine a new base_time
@@ -128,8 +196,22 @@ static void pmu_update_cycles(CPUPPCState *env)
  */
 static void start_cycle_count_session(CPUPPCState *env)
 {
-    /* Just define pmu_base_time for now */
-    env->pmu_base_time = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
+    bool overflow_enabled = env->spr[SPR_POWER_MMCR0] &
+                            (MMCR0_PMC1CE | MMCR0_PMCjCE);
+
+    /*
+     * Always delete existing overflow timers when starting a
+     * new cycle counting session.
+     */
+    pmu_delete_timers(env);
+
+    if (!overflow_enabled) {
+        /* Define pmu_base_time and leave */
+        env->pmu_base_time = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
+        return;
+    }
+
+    pmu_start_overflow_timers(env);
 }
 
 void helper_store_mmcr0(CPUPPCState *env, target_ulong value)
-- 
2.31.1