hw/core/reset: Implement qemu_register_reset via qemu_register_resettable

Reimplement qemu_register_reset() via qemu_register_resettable().

We define a new LegacyReset object which implements Resettable and
defines its reset hold phase method to call a QEMUResetHandler
function.  When qemu_register_reset() is called, we create a new
LegacyReset object and add it to the simulation_reset
ResettableContainer.  When qemu_unregister_reset() is called, we find
the LegacyReset object in the container and remove it.

This implementation of qemu_unregister_reset() means we'll end up
scanning the ResetContainer's list of child objects twice, once
to find the LegacyReset object, and once in g_ptr_array_remove().
In theory we could avoid this by having the ResettableContainer
interface include a resettable_container_remove_with_equal_func()
that took a callback method so that we could use
g_ptr_array_find_with_equal_func() and g_ptr_array_remove_index().
But we don't expect qemu_unregister_reset() to be called frequently
or in hot paths, and we expect the simulation_reset container to
usually not have many children.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-id: 20240220160622.114437-9-peter.maydell@linaro.org
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>

1 files changed, 5 insertions, 2 deletions

diff --git a/include/sysemu/reset.h b/include/sysemu/reset.h
index ef2c595..ae43604 100644
--- a/include/sysemu/reset.h
+++ b/include/sysemu/reset.h
@@ -67,8 +67,11 @@ void qemu_unregister_resettable(Object *obj);
  * @opaque: opaque data to pass to @func
  *
  * Register @func on the list of functions which are called when the
- * entire system is reset. The functions are called in the order in
- * which they are registered.
+ * entire system is reset. Functions registered with this API and
+ * Resettable objects registered with qemu_register_resettable() are
+ * handled together, in the order in which they were registered.
+ * Functions registered with this API are called in the 'hold' phase
+ * of the 3-phase reset.
  *
  * In general this function should not be used in new code where possible;
  * for instance, device model reset is better accomplished using the