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/openrisc/interrupt.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/target/openrisc/interrupt.c b/target/openrisc/interrupt.c
index 3eab771dcd..361f242954 100644
--- a/target/openrisc/interrupt.c
+++ b/target/openrisc/interrupt.c
@@ -28,6 +28,10 @@
 
 void openrisc_cpu_do_interrupt(CPUState *cs)
 {
+    bool bql = !qemu_mutex_iothread_locked();
+    if (bql) {
+        qemu_mutex_lock_iothread();
+    }
 #ifndef CONFIG_USER_ONLY
     OpenRISCCPU *cpu = OPENRISC_CPU(cs);
     CPUOpenRISCState *env = &cpu->env;
@@ -99,6 +103,9 @@ void openrisc_cpu_do_interrupt(CPUState *cs)
 #endif
 
     cs->exception_index = -1;
+    if (bql) {
+        qemu_mutex_unlock_iothread();
+    }
 }
 
 bool openrisc_cpu_exec_interrupt(CPUState *cs, int interrupt_request)
@@ -106,6 +113,7 @@ bool openrisc_cpu_exec_interrupt(CPUState *cs, int interrupt_request)
     OpenRISCCPU *cpu = OPENRISC_CPU(cs);
     CPUOpenRISCState *env = &cpu->env;
     int idx = -1;
+    qemu_mutex_lock_iothread();
 
     if ((interrupt_request & CPU_INTERRUPT_HARD) && (env->sr & SR_IEE)) {
         idx = EXCP_INT;
@@ -116,7 +124,9 @@ bool openrisc_cpu_exec_interrupt(CPUState *cs, int interrupt_request)
     if (idx >= 0) {
         cs->exception_index = idx;
         openrisc_cpu_do_interrupt(cs);
+        qemu_mutex_unlock_iothread();
         return true;
     }
+    qemu_mutex_unlock_iothread();
     return false;
 }
-- 
2.17.1