[PATCH v2 12/16] target/ppc/power8_pmu.c: enable PMC1 counter negative overflow

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

This patch starts the counter negative EBB support by enabling PMC1
counter negative overflow when PMC1 is counting cycles.

A counter negative overflow happens when a performance monitor counter
reaches the value 0x80000000. When that happens, if counter negative
condition events are enabled in that counter, a performance monitor
alert is triggered. For PMC1, this condition is enabled by MMCR0_PMC1CE.

Cycle counting is done by calculating elapsed time between the time
the PMU started to run and when the PMU is shut down. Our clock is
fixed in 1Ghz, so 1 cycle equals 1 nanoseconds. The same idea is used to
predict a counter negative overflow: calculate the amount of nanoseconds
for the timer to reach 0x80000000, start a timer with it and trigger the
performance monitor alert. If event-based exceptions are enabled (bit
MMCR0_EBE), we'll go ahead and fire a PPC_INTERRUPT_PMC.

A new function 'start_cycle_count_session' was added to encapsulate the
most common steps of cycle calculation: redefine base time and start
overflow timers. This will avoid code repetition in the next patches.

Counter overflow for the remaining counters will be added shortly.

Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
---
 target/ppc/cpu.h        |  1 +
 target/ppc/power8_pmu.c | 96 +++++++++++++++++++++++++++++++++--------
 2 files changed, 79 insertions(+), 18 deletions(-)

diff --git a/target/ppc/cpu.h b/target/ppc/cpu.h
index 535754ddff..b9d5dca983 100644
--- a/target/ppc/cpu.h
+++ b/target/ppc/cpu.h
@@ -352,6 +352,7 @@ typedef struct ppc_v3_pate_t {
 #define MMCR0_PMCC  PPC_BITMASK(44, 45) /* PMC Control */
 #define MMCR0_FC14 PPC_BIT(58)
 #define MMCR0_FC56 PPC_BIT(59)
+#define MMCR0_PMC1CE PPC_BIT(48)
 
 #define MMCR1_PMC1SEL_SHIFT (63 - 39)
 #define MMCR1_PMC1SEL PPC_BITMASK(32, 39)
diff --git a/target/ppc/power8_pmu.c b/target/ppc/power8_pmu.c
index a57b602125..d10f371b5f 100644
--- a/target/ppc/power8_pmu.c
+++ b/target/ppc/power8_pmu.c
@@ -33,6 +33,8 @@ static void update_PMC_PM_CYC(CPUPPCState *env, int sprn,
     env->spr[sprn] += time_delta;
 }
 
+#define COUNTER_NEGATIVE_VAL 0x80000000
+
 static uint8_t get_PMC_event(CPUPPCState *env, int sprn)
 {
     int event = 0x0;
@@ -116,30 +118,88 @@ static void update_cycles_PMCs(CPUPPCState *env)
     }
 }
 
+static int64_t get_CYC_timeout(CPUPPCState *env, int sprn)
+{
+    int64_t remaining_cyc;
+
+    if (env->spr[sprn] >= COUNTER_NEGATIVE_VAL) {
+        return 0;
+    }
+
+    remaining_cyc = COUNTER_NEGATIVE_VAL - env->spr[sprn];
+    return remaining_cyc;
+}
+
+static bool counter_negative_cond_enabled(uint64_t mmcr0)
+{
+    return mmcr0 & MMCR0_PMC1CE;
+}
+
+/*
+ * A cycle count session consists of the basic operations we
+ * need to do to support PM_CYC events: redefine a new base_time
+ * to be used to calculate PMC values and start overflow timers.
+ */
+static void start_cycle_count_session(CPUPPCState *env)
+{
+    uint64_t now = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
+    uint64_t timeout;
+
+    env->pmu_base_time = now;
+
+    /*
+     * Always delete existing overflow timers when starting a
+     * new cycle counting session.
+     */
+    timer_del(env->pmu_intr_timers[0]);
+
+    if (!counter_negative_cond_enabled(env->spr[SPR_POWER_MMCR0])) {
+        return;
+    }
+
+    if (!pmc_is_running(env, SPR_POWER_PMC1)) {
+        return;
+    }
+
+    if (!(env->spr[SPR_POWER_MMCR0] & MMCR0_PMC1CE)) {
+        return;
+    }
+
+    switch (get_PMC_event(env, SPR_POWER_PMC1)) {
+    case 0xF0:
+    case 0x1E:
+        timeout = get_CYC_timeout(env, SPR_POWER_PMC1);
+        break;
+    default:
+        return;
+    }
+
+    timer_mod(env->pmu_intr_timers[0], now + timeout);
+}
+
 static void cpu_ppc_pmu_timer_cb(void *opaque)
 {
     PowerPCCPU *cpu = opaque;
     CPUPPCState *env = &cpu->env;
-    uint64_t mmcr0;
-
-    mmcr0 = env->spr[SPR_POWER_MMCR0];
-    if (env->spr[SPR_POWER_MMCR0] & MMCR0_EBE) {
-        /* freeeze counters if needed */
-        if (mmcr0 & MMCR0_FCECE) {
-            mmcr0 &= ~MMCR0_FCECE;
-            mmcr0 |= MMCR0_FC;
-        }
 
-        /* Clear PMAE and set PMAO */
-        if (mmcr0 & MMCR0_PMAE) {
-            mmcr0 &= ~MMCR0_PMAE;
-            mmcr0 |= MMCR0_PMAO;
-        }
-        env->spr[SPR_POWER_MMCR0] = mmcr0;
+    if (!(env->spr[SPR_POWER_MMCR0] & MMCR0_EBE)) {
+        return;
+    }
 
-        /* Fire the PMC hardware exception */
-        ppc_set_irq(cpu, PPC_INTERRUPT_PMC, 1);
+    if (env->spr[SPR_POWER_MMCR0] & MMCR0_FCECE) {
+        env->spr[SPR_POWER_MMCR0] &= ~MMCR0_FCECE;
+        env->spr[SPR_POWER_MMCR0] |= MMCR0_FC;
     }
+
+    update_cycles_PMCs(env);
+
+    if (env->spr[SPR_POWER_MMCR0] & MMCR0_PMAE) {
+        env->spr[SPR_POWER_MMCR0] &= ~MMCR0_PMAE;
+        env->spr[SPR_POWER_MMCR0] |= MMCR0_PMAO;
+    }
+
+    /* Fire the PMC hardware exception */
+    ppc_set_irq(cpu, PPC_INTERRUPT_PMC, 1);
 }
 
 void cpu_ppc_pmu_timer_init(CPUPPCState *env)
@@ -182,7 +242,7 @@ void helper_store_mmcr0(CPUPPCState *env, target_ulong value)
         if (!curr_FC) {
             update_cycles_PMCs(env);
         } else {
-            env->pmu_base_time = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
+            start_cycle_count_session(env);
         }
     }
 }
-- 
2.31.1