[PATCH v1 19/21] target/sparc: 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/sparc/cpu.c          |  3 +++
 target/sparc/int32_helper.c | 13 ++++++++++++-
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/target/sparc/cpu.c b/target/sparc/cpu.c
index 20c7c0c434..13b5a038e8 100644
--- a/target/sparc/cpu.c
+++ b/target/sparc/cpu.c
@@ -79,6 +79,7 @@ static void sparc_cpu_reset(DeviceState *dev)
 
 static bool sparc_cpu_exec_interrupt(CPUState *cs, int interrupt_request)
 {
+    qemu_mutex_lock_iothread();
     if (interrupt_request & CPU_INTERRUPT_HARD) {
         SPARCCPU *cpu = SPARC_CPU(cs);
         CPUSPARCState *env = &cpu->env;
@@ -90,10 +91,12 @@ static bool sparc_cpu_exec_interrupt(CPUState *cs, int interrupt_request)
             if (type != TT_EXTINT || cpu_pil_allowed(env, pil)) {
                 cs->exception_index = env->interrupt_index;
                 sparc_cpu_do_interrupt(cs);
+                qemu_mutex_unlock_iothread();
                 return true;
             }
         }
     }
+    qemu_mutex_unlock_iothread();
     return false;
 }
 
diff --git a/target/sparc/int32_helper.c b/target/sparc/int32_helper.c
index 9a71e1abd8..3940e945ed 100644
--- a/target/sparc/int32_helper.c
+++ b/target/sparc/int32_helper.c
@@ -69,7 +69,12 @@ void sparc_cpu_do_interrupt(CPUState *cs)
 {
     SPARCCPU *cpu = SPARC_CPU(cs);
     CPUSPARCState *env = &cpu->env;
-    int cwp, intno = cs->exception_index;
+    int cwp, intno;
+    bool bql = !qemu_mutex_iothread_locked();
+    if (bql) {
+        qemu_mutex_lock_iothread();
+    }
+    intno = cs->exception_index;
 
     /* Compute PSR before exposing state.  */
     if (env->cc_op != CC_OP_FLAGS) {
@@ -115,6 +120,9 @@ void sparc_cpu_do_interrupt(CPUState *cs)
                           "Error state",
                       cs->exception_index, excp_name_str(cs->exception_index));
         }
+        if (bql) {
+            qemu_mutex_unlock_iothread();
+        }
         return;
     }
 #endif
@@ -136,6 +144,9 @@ void sparc_cpu_do_interrupt(CPUState *cs)
         env->qemu_irq_ack(env, env->irq_manager, intno);
     }
 #endif
+    if (bql) {
+        qemu_mutex_unlock_iothread();
+    }
 }
 
 #if !defined(CONFIG_USER_ONLY)
-- 
2.17.1