[PATCH v3 32/32] target/arm: implement WFET

["Alex Bennée" <alex.bennee@linaro.org>]

Now we have the event stream and SEV/SEVL implemented we can finally
enable WFET for Aarch64.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

---
v2
  - fix exception syndrome by using enum value
  - use env->halt_reason
v3
  - fix check_wfx_trap(s/false/true/) as it is a WFE
---
 target/arm/tcg/helper-defs.h   |  1 +
 target/arm/tcg/op_helper.c     | 80 ++++++++++++++++++++++++++++++++++
 target/arm/tcg/translate-a64.c | 15 ++++---
 3 files changed, 89 insertions(+), 7 deletions(-)

diff --git a/target/arm/tcg/helper-defs.h b/target/arm/tcg/helper-defs.h
index ebdf09be38a..5e4d828dd55 100644
--- a/target/arm/tcg/helper-defs.h
+++ b/target/arm/tcg/helper-defs.h
@@ -56,6 +56,7 @@ DEF_HELPER_1(setend, void, env)
 DEF_HELPER_2(wfi, void, env, i32)
 DEF_HELPER_2(wfe, void, env, i32)
 DEF_HELPER_2(wfit, void, env, i32)
+DEF_HELPER_2(wfet, void, env, i32)
 DEF_HELPER_1(yield, void, env)
 DEF_HELPER_1(pre_hvc, void, env)
 DEF_HELPER_2(pre_smc, void, env, i32)
diff --git a/target/arm/tcg/op_helper.c b/target/arm/tcg/op_helper.c
index fe34c94e890..112e0c2eb1a 100644
--- a/target/arm/tcg/op_helper.c
+++ b/target/arm/tcg/op_helper.c
@@ -620,6 +620,86 @@ void HELPER(wfe)(CPUARMState *env, uint32_t insn_len)
 #endif
 }
 
+void HELPER(wfet)(CPUARMState *env, uint32_t rd)
+{
+#ifdef CONFIG_USER_ONLY
+    /*
+     * As for WFIT make it NOP here, because trying to raise EXCP_HLT
+     * would trigger an abort.
+     */
+    return;
+#else
+    ARMCPU *cpu = env_archcpu(env);
+    CPUState *cs = env_cpu(env);
+    uint32_t excp;
+    int target_el = check_wfx_trap(env, true, &excp);
+    /* The WFET should time out when CNTVCT_EL0 >= the specified value. */
+    uint64_t cntval = gt_get_countervalue(env);
+    uint64_t timeout = env->xregs[rd];
+    /*
+     * We want the value that we would get if we read CNTVCT_EL0 from
+     * the current exception level, so the direct_access offset, not
+     * the indirect_access one. Compare the pseudocode LocalTimeoutEvent(),
+     * which calls VirtualCounterTimer().
+     */
+    uint64_t offset = gt_direct_access_timer_offset(env, GTIMER_VIRT);
+    uint64_t cntvct = cntval - offset;
+    uint64_t nexttick;
+    int64_t next_event;
+
+    /*
+     * As for WFE if the event register is already set we can consume
+     * the event and return immediately.
+     */
+    if (env->event_register) {
+        env->event_register = false;
+        return;
+    }
+
+
+    if (cpu_has_work(cs) || cntvct >= timeout) {
+        /*
+         * Don't bother to go into our "low power state" if
+         * we would just wake up immediately.
+         */
+        return;
+    }
+
+    /* We might sleep, so now we check to see if we should trap */
+    if (target_el) {
+        env->pc -= 4;
+        raise_exception(env, excp, syn_wfx(1, 0xe, rd, true, WFET, false), target_el);
+    }
+
+    /*
+     * Finally work out if the timeout or event stream will kick in
+     * earlier.
+     */
+    if (uadd64_overflow(timeout, offset, &nexttick)) {
+        nexttick = UINT64_MAX;
+    }
+    if (nexttick > INT64_MAX / gt_cntfrq_period_ns(cpu)) {
+        nexttick = INT64_MAX;
+    }
+
+    next_event = gt_calc_next_event_stream(env);
+    if (next_event > 0 && next_event < nexttick) {
+        timer_mod(cpu->wfxt_timer, next_event);
+    } else {
+        if (nexttick == INT64_MAX) {
+            timer_mod_ns(cpu->wfxt_timer, INT64_MAX);
+        } else {
+            timer_mod(cpu->wfxt_timer, nexttick);
+        }
+    }
+
+    env->halt_reason = HALT_WFE;
+    cs->exception_index = EXCP_HLT;
+    cs->halted = 1;
+    cpu_loop_exit(cs);
+#endif
+}
+
 void HELPER(yield)(CPUARMState *env)
 {
     CPUState *cs = env_cpu(env);
diff --git a/target/arm/tcg/translate-a64.c b/target/arm/tcg/translate-a64.c
index 83b2a6e848f..c8c8a27956b 100644
--- a/target/arm/tcg/translate-a64.c
+++ b/target/arm/tcg/translate-a64.c
@@ -2093,14 +2093,15 @@ static bool trans_WFET(DisasContext *s, arg_WFET *a)
         return false;
     }
 
-    /*
-     * We rely here on our WFE implementation being a NOP, so we
-     * don't need to do anything different to handle the WFET timeout
-     * from what trans_WFE does.
-     */
-    if (!(tb_cflags(s->base.tb) & CF_PARALLEL)) {
-        s->base.is_jmp = DISAS_WFE;
+    if (s->ss_active) {
+        /* Act like a NOP under architectural singlestep */
+        return true;
     }
+
+    gen_a64_update_pc(s, 4);
+    gen_helper_wfet(tcg_env, tcg_constant_i32(a->rd));
+    /* Go back to the main loop to check for interrupts */
+    s->base.is_jmp = DISAS_EXIT;
     return true;
 }
 
-- 
2.47.3