From 310616d3677aad709d3eaf8f5f08683f2853f227 Mon Sep 17 00:00:00 2001 From: Damien Hedde Date: Thu, 20 Oct 2022 15:27:49 +0100 Subject: [PATCH] hw/core/resettable: fix reset level counting MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit The code for handling the reset level count in the Resettable code has two issues: The reset count is only decremented for the 1->0 case. This means that if there's ever a nested reset that takes the count to 2 then it will never again be decremented. Eventually the count will exceed the '50' limit in resettable_phase_enter() and QEMU will trip over the assertion failure. The repro case in issue 1266 is an example of this that happens now the SCSI subsystem uses three-phase reset. Secondly, the count is decremented only after the exit phase handler is called. Moving the reset count decrement from "just after" to "just before" calling the exit phase handler allows resettable_is_in_reset() to return 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" as a special case. Note that the semantics change to the *_is_in_reset() functions will have no effect on the current codebase, because only two devices (hw/char/cadence_uart.c and hw/misc/zynq_sclr.c) currently call those functions, and in neither case do they do it from the device's exit phase methed. Fixes: 4a5fc890 ("scsi: Use device_cold_reset() and bus_cold_reset()") Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1266 Signed-off-by: Damien Hedde Signed-off-by: Peter Maydell Reported-by: Michael Peter Reviewed-by: Philippe Mathieu-Daudé Message-id: 20221020142749.3357951-1-peter.maydell@linaro.org Buglink: https://bugs.launchpad.net/qemu/+bug/1905297 Reported-by: Michael Peter [PMM: adjust the docs paragraph changed to get the name of the 'enter' phase right and to clarify exactly when the count is adjusted; rewrite the commit message] Signed-off-by: Peter Maydell --- docs/devel/reset.rst | 8 +++++--- hw/core/resettable.c | 3 +-- 2 files changed, 6 insertions(+), 5 deletions(-) diff --git a/docs/devel/reset.rst b/docs/devel/reset.rst index abea1102dc..7cc6a6b314 100644 --- a/docs/devel/reset.rst +++ b/docs/devel/reset.rst @@ -210,9 +210,11 @@ 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 *enter* phase (before +either its children or its own enter method is called) to the *exit* +phase. During *enter* and *hold* phase only, the function will return that the +object is in reset. The state is changed after the *exit* is propagated to +its children and just before calling the object's own *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); -- 2.11.4.GIT