[PATCH v1 18/21] target/sh4: add BQL to do_interrupt and cpu_exec_interrupt

[Robert Foley <robert.foley@linaro.org>]

This is part of a series of changes to remove the implied BQL
from the common code of cpu_handle_interrupt and
cpu_handle_exception.  As part of removing the implied BQL
from the common code, we are pushing the BQL holding
down into the per-arch implementation functions of
do_interrupt and cpu_exec_interrupt.

The purpose of this set of changes is to set the groundwork
so that an arch could move towards removing
the BQL from the cpu_handle_interrupt/exception paths.

This approach was suggested by Paolo Bonzini.
For reference, here are two key posts in the discussion, explaining
the reasoning/benefits of this approach.
https://lists.gnu.org/archive/html/qemu-devel/2020-07/msg08731.html
https://lists.gnu.org/archive/html/qemu-devel/2020-08/msg00044.html

Signed-off-by: Robert Foley <robert.foley@linaro.org>
---
 target/sh4/helper.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/target/sh4/helper.c b/target/sh4/helper.c
index 1e32365c75..c4d5b9a374 100644
--- a/target/sh4/helper.c
+++ b/target/sh4/helper.c
@@ -62,8 +62,11 @@ void superh_cpu_do_interrupt(CPUState *cs)
 {
     SuperHCPU *cpu = SUPERH_CPU(cs);
     CPUSH4State *env = &cpu->env;
-    int do_irq = cpu_interrupt_request(cs) & CPU_INTERRUPT_HARD;
-    int do_exp, irq_vector = cs->exception_index;
+    int do_irq;
+    int do_exp, irq_vector;
+    qemu_mutex_lock_iothread();
+    do_irq = cpu_interrupt_request(cs) & CPU_INTERRUPT_HARD;
+    irq_vector = cs->exception_index;
 
     /* prioritize exceptions over interrupts */
 
@@ -79,9 +82,11 @@ void superh_cpu_do_interrupt(CPUState *cs)
                should be loaded with the kernel entry point.
                qemu_system_reset_request takes care of that.  */
             qemu_system_reset_request(SHUTDOWN_CAUSE_GUEST_RESET);
+            qemu_mutex_unlock_iothread();
             return;
         }
         if (do_irq && !env->in_sleep) {
+            qemu_mutex_unlock_iothread();
             return; /* masked */
         }
     }
@@ -91,6 +96,7 @@ void superh_cpu_do_interrupt(CPUState *cs)
         irq_vector = sh_intc_get_pending_vector(env->intc_handle,
 						(env->sr >> 4) & 0xf);
         if (irq_vector == -1) {
+            qemu_mutex_unlock_iothread();
             return; /* masked */
 	}
     }
@@ -180,14 +186,17 @@ void superh_cpu_do_interrupt(CPUState *cs)
             env->pc = env->vbr + 0x100;
             break;
         }
+        qemu_mutex_unlock_iothread();
         return;
     }
 
     if (do_irq) {
         env->intevt = irq_vector;
         env->pc = env->vbr + 0x600;
+        qemu_mutex_unlock_iothread();
         return;
     }
+    qemu_mutex_unlock_iothread();
 }
 
 static void update_itlb_use(CPUSH4State * env, int itlbnb)
-- 
2.17.1