target/riscv: Do not setup pmu timer if OF is disabled

The timer is setup function is invoked in both hpmcounter
write and mcountinhibit write path. If the OF bit set, the
LCOFI interrupt is disabled. There is no benefitting in
setting up the qemu timer until LCOFI is cleared to indicate
that interrupts can be fired again.

Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Signed-off-by: Atish Patra <atishp@rivosinc.com>
Message-ID: <20240711-smcntrpmf_v7-v8-12-b7c38ae7b263@rivosinc.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

Author: atishp04

target/riscv/pmu.c

@@ -416,14 +416,49 @@ int riscv_pmu_update_event_map(CPURISCVState *env, uint64_t value,
     return 0;
 }
 
+static bool pmu_hpmevent_is_of_set(CPURISCVState *env, uint32_t ctr_idx)
+{
+    target_ulong mhpmevent_val;
+    uint64_t of_bit_mask;
+
+    if (riscv_cpu_mxl(env) == MXL_RV32) {
+        mhpmevent_val = env->mhpmeventh_val[ctr_idx];
+        of_bit_mask = MHPMEVENTH_BIT_OF;
+     } else {
+        mhpmevent_val = env->mhpmevent_val[ctr_idx];
+        of_bit_mask = MHPMEVENT_BIT_OF;
+    }
+
+    return get_field(mhpmevent_val, of_bit_mask);
+}
+
+static bool pmu_hpmevent_set_of_if_clear(CPURISCVState *env, uint32_t ctr_idx)
+{
+    target_ulong *mhpmevent_val;
+    uint64_t of_bit_mask;
+
+    if (riscv_cpu_mxl(env) == MXL_RV32) {
+        mhpmevent_val = &env->mhpmeventh_val[ctr_idx];
+        of_bit_mask = MHPMEVENTH_BIT_OF;
+     } else {
+        mhpmevent_val = &env->mhpmevent_val[ctr_idx];
+        of_bit_mask = MHPMEVENT_BIT_OF;
+    }
+
+    if (!get_field(*mhpmevent_val, of_bit_mask)) {
+        *mhpmevent_val |= of_bit_mask;
+        return true;
+    }
+
+    return false;
+}
+
 static void pmu_timer_trigger_irq(RISCVCPU *cpu,
                                   enum riscv_pmu_event_idx evt_idx)
 {
     uint32_t ctr_idx;
     CPURISCVState *env = &cpu->env;
     PMUCTRState *counter;
-    target_ulong *mhpmevent_val;
-    uint64_t of_bit_mask;
     int64_t irq_trigger_at;
     uint64_t curr_ctr_val, curr_ctrh_val;
     uint64_t ctr_val;
@@ -439,12 +474,9 @@ static void pmu_timer_trigger_irq(RISCVCPU *cpu,
         return;
     }
 
-    if (riscv_cpu_mxl(env) == MXL_RV32) {
-        mhpmevent_val = &env->mhpmeventh_val[ctr_idx];
-        of_bit_mask = MHPMEVENTH_BIT_OF;
-     } else {
-        mhpmevent_val = &env->mhpmevent_val[ctr_idx];
-        of_bit_mask = MHPMEVENT_BIT_OF;
+    /* Generate interrupt only if OF bit is clear */
+    if (pmu_hpmevent_is_of_set(env, ctr_idx)) {
+        return;
     }
 
     counter = &env->pmu_ctrs[ctr_idx];
@@ -477,9 +509,7 @@ static void pmu_timer_trigger_irq(RISCVCPU *cpu,
     }
 
     if (cpu->pmu_avail_ctrs & BIT(ctr_idx)) {
-        /* Generate interrupt only if OF bit is clear */
-        if (!(*mhpmevent_val & of_bit_mask)) {
-            *mhpmevent_val |= of_bit_mask;
+        if (pmu_hpmevent_set_of_if_clear(env, ctr_idx)) {
             riscv_cpu_update_mip(env, MIP_LCOFIP, BOOL_TO_MASK(1));
         }
     }
@@ -502,7 +532,9 @@ int riscv_pmu_setup_timer(CPURISCVState *env, uint64_t value, uint32_t ctr_idx)
     RISCVCPU *cpu = env_archcpu(env);
     PMUCTRState *counter = &env->pmu_ctrs[ctr_idx];
 
-    if (!riscv_pmu_counter_valid(cpu, ctr_idx) || !cpu->cfg.ext_sscofpmf) {
+    /* No need to setup a timer if LCOFI is disabled when OF is set */
+    if (!riscv_pmu_counter_valid(cpu, ctr_idx) || !cpu->cfg.ext_sscofpmf ||
+        pmu_hpmevent_is_of_set(env, ctr_idx)) {
         return -1;
     }