[PATCH v2] hw/core/resettable: make in-reset state false during exit phase call

[Damien Hedde <damien.hedde@greensocs.com>]

Move the reset count decrement from "just after" to "just before"
calling the exit phase handler. The goal is to make
resettable_is_in_reset() returning false during the handler execution.

This simplifies reset handling in resettable devices.

Typically, a function that updates the device state will just need
to read the current reset state and not anymore treat the "in
a reset-exit transition" special case.

As a side note, this patch also fixes the fact that the reset count was
not decremented in case of recursive reset.

Signed-off-by: Damien Hedde <damien.hedde@greensocs.com>
Buglink: https://bugs.launchpad.net/qemu/+bug/1905297
Reported-by: Michael Peter <michael.peter@hensoldt-cyber.com>
--

Hi,

Following our discussion:
https://lists.nongnu.org/archive/html/qemu-devel/2021-01/msg01013.html
here's my proposal to fix Michael's bug on a global scope.

I flaged it v2 because I've taken Philippe's remarks there:
https://lists.nongnu.org/archive/html/qemu-devel/2020-12/msg00635.html
I've also changed the patch title, I think it is better this way.

Thanks,
Damien

Cc: f4bug@amsat.org
Cc: peter.maydell@linaro.org
Cc: alistair@alistair23.me
Cc: edgar.iglesias@gmail.com
---
 docs/devel/reset.rst | 6 +++---
 hw/core/resettable.c | 3 +--
 2 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/docs/devel/reset.rst b/docs/devel/reset.rst
index abea1102dc..021a7277a2 100644
--- a/docs/devel/reset.rst
+++ b/docs/devel/reset.rst
@@ -210,9 +210,9 @@ Polling the reset state
 Resettable interface provides the ``resettable_is_in_reset()`` function.
 This function returns true if the object parameter is currently under reset.
 
-An object is under reset from the beginning of the *init* phase to the end of
-the *exit* phase. During all three phases, the function will return that the
-object is in reset.
+An object is under reset from the beginning of the *init* phase to the *exit*
+phase. During *init* and *hold* phase only, the function will return that the
+object is in reset. The state is changed just before calling the *exit* method.
 
 This function may be used if the object behavior has to be adapted
 while in reset state. For example if a device has an irq input,
diff --git a/hw/core/resettable.c b/hw/core/resettable.c
index 96a99ce39e..c3df75c6ba 100644
--- a/hw/core/resettable.c
+++ b/hw/core/resettable.c
@@ -201,12 +201,11 @@ static void resettable_phase_exit(Object *obj, void *opaque, ResetType type)
     resettable_child_foreach(rc, obj, resettable_phase_exit, NULL, type);
 
     assert(s->count > 0);
-    if (s->count == 1) {
+    if (--s->count == 0) {
         trace_resettable_phase_exit_exec(obj, obj_typename, !!rc->phases.exit);
         if (rc->phases.exit && !resettable_get_tr_func(rc, obj)) {
             rc->phases.exit(obj);
         }
-        s->count = 0;
     }
     s->exit_phase_in_progress = false;
     trace_resettable_phase_exit_end(obj, obj_typename, s->count);
-- 
2.29.2