target/nios2: Rewrite interrupt handling

Previously, we would avoid setting CPU_INTERRUPT_HARD when interrupts
are disabled at a particular point in time, instead queuing the value
into cpu->irq_pending.  This is more complicated than required.

Instead, set CPU_INTERRUPT_HARD any time there is a pending interrupt,
and exclusively check for interrupts disabled in nios2_cpu_exec_interrupt.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

target/nios2/cpu.c

@@ -73,12 +73,9 @@ static void nios2_cpu_set_irq(void *opaque, int irq, int level)
 
     env->regs[CR_IPENDING] = deposit32(env->regs[CR_IPENDING], irq, 1, !!level);
 
-    env->irq_pending = env->regs[CR_IPENDING] & env->regs[CR_IENABLE];
+    if (env->regs[CR_IPENDING]) {
-
-    if (env->irq_pending && (env->regs[CR_STATUS] & CR_STATUS_PIE)) {
-        env->irq_pending = 0;
         cpu_interrupt(cs, CPU_INTERRUPT_HARD);
-    } else if (!env->irq_pending) {
+    } else {
         cpu_reset_interrupt(cs, CPU_INTERRUPT_HARD);
     }
 }
@@ -134,7 +131,8 @@ static bool nios2_cpu_exec_interrupt(CPUState *cs, int interrupt_request)
     CPUNios2State *env = &cpu->env;
 
     if ((interrupt_request & CPU_INTERRUPT_HARD) &&
-        (env->regs[CR_STATUS] & CR_STATUS_PIE)) {
+        (env->regs[CR_STATUS] & CR_STATUS_PIE) &&
+        (env->regs[CR_IPENDING] & env->regs[CR_IENABLE])) {
         cs->exception_index = EXCP_IRQ;
         nios2_cpu_do_interrupt(cs);
         return true;

target/nios2/cpu.h

@@ -160,7 +160,6 @@ struct CPUNios2State {
 
 #if !defined(CONFIG_USER_ONLY)
     Nios2MMU mmu;
-    uint32_t irq_pending;
 #endif
     int error_code;
 };

target/nios2/helper.h

@@ -24,5 +24,4 @@ DEF_HELPER_FLAGS_2(raise_exception, TCG_CALL_NO_WG, noreturn, env, i32)
 DEF_HELPER_2(mmu_write_tlbacc, void, env, i32)
 DEF_HELPER_2(mmu_write_tlbmisc, void, env, i32)
 DEF_HELPER_2(mmu_write_pteaddr, void, env, i32)
-DEF_HELPER_1(check_interrupts, void, env)
 #endif

target/nios2/op_helper.c

@@ -21,28 +21,9 @@
 #include "qemu/osdep.h"
 #include "cpu.h"
 #include "exec/helper-proto.h"
-#include "exec/cpu_ldst.h"
 #include "exec/exec-all.h"
 #include "qemu/main-loop.h"
 
-#if !defined(CONFIG_USER_ONLY)
-static void nios2_check_interrupts(CPUNios2State *env)
-{
-    if (env->irq_pending &&
-        (env->regs[CR_STATUS] & CR_STATUS_PIE)) {
-        env->irq_pending = 0;
-        cpu_interrupt(env_cpu(env), CPU_INTERRUPT_HARD);
-    }
-}
-
-void helper_check_interrupts(CPUNios2State *env)
-{
-    qemu_mutex_lock_iothread();
-    nios2_check_interrupts(env);
-    qemu_mutex_unlock_iothread();
-}
-#endif /* !CONFIG_USER_ONLY */
-
 void helper_raise_exception(CPUNios2State *env, uint32_t index)
 {
     CPUState *cs = env_cpu(env);

target/nios2/translate.c

@@ -491,19 +491,15 @@ static void wrctl(DisasContext *dc, uint32_t code, uint32_t flags)
     case CR_IPENDING:
         /* ipending is read only, writes ignored. */
         break;
+    case CR_STATUS:
+    case CR_IENABLE:
+        /* If interrupts were enabled using WRCTL, trigger them. */
+        dc->base.is_jmp = DISAS_UPDATE;
+        /* fall through */
     default:
         tcg_gen_mov_tl(cpu_R[instr.imm5 + CR_BASE], v);
         break;
     }
-
-    /* If interrupts were enabled using WRCTL, trigger them. */
-    if ((instr.imm5 + CR_BASE) == CR_STATUS) {
-        if (tb_cflags(dc->base.tb) & CF_USE_ICOUNT) {
-            gen_io_start();
-        }
-        gen_helper_check_interrupts(cpu_env);
-        dc->base.is_jmp = DISAS_UPDATE;
-    }
 #endif
 }