[PATCH v1 21/21] target/xtensa: 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/xtensa/exc_helper.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/target/xtensa/exc_helper.c b/target/xtensa/exc_helper.c
index 01d1e56feb..fd33a56847 100644
--- a/target/xtensa/exc_helper.c
+++ b/target/xtensa/exc_helper.c
@@ -200,6 +200,7 @@ void xtensa_cpu_do_interrupt(CPUState *cs)
     XtensaCPU *cpu = XTENSA_CPU(cs);
     CPUXtensaState *env = &cpu->env;
 
+    qemu_mutex_lock_iothread();
     if (cs->exception_index == EXC_IRQ) {
         qemu_log_mask(CPU_LOG_INT,
                       "%s(EXC_IRQ) level = %d, cintlevel = %d, "
@@ -252,6 +253,7 @@ void xtensa_cpu_do_interrupt(CPUState *cs)
         break;
     }
     check_interrupts(env);
+    qemu_mutex_unlock_iothread();
 }
 #else
 void xtensa_cpu_do_interrupt(CPUState *cs)
-- 
2.17.1