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 <damien.hedde@greensocs.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reported-by: Michael Peter <michael.peter@hensoldt-cyber.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-id: 20221020142749.3357951-1-peter.maydell@linaro.org
Buglink: https://bugs.launchpad.net/qemu/+bug/1905297
Reported-by: Michael Peter <michael.peter@hensoldt-cyber.com>
[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 <peter.maydell@linaro.org>
Deprecate device_legacy_reset(), qdev_reset_all() and
qbus_reset_all() to be replaced by new functions
device_cold_reset() and bus_cold_reset() which uses resettable API.
Also introduce resettable_cold_reset_fn() which may be used as a
replacement for qdev_reset_all_fn and qbus_reset_all_fn().
Following patches will be needed to look at legacy reset call sites
and switch to resettable api. The legacy functions will be removed
when unused.
Signed-off-by: Damien Hedde <damien.hedde@greensocs.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20200123132823.1117486-9-damien.hedde@greensocs.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Add a function resettable_change_parent() to do the required
plumbing when changing the parent a of Resettable object.
We need to make sure that the reset state of the object remains
coherent with the reset state of the new parent.
We make the 2 following hypothesis:
+ when an object is put in a parent under reset, the object goes in
reset.
+ when an object is removed from a parent under reset, the object
leaves reset.
The added function avoids any glitch if both old and new parent are
already in reset.
Signed-off-by: Damien Hedde <damien.hedde@greensocs.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20200123132823.1117486-6-damien.hedde@greensocs.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
This commit defines an interface allowing multi-phase reset. This aims
to solve a problem of the actual single-phase reset (built in
DeviceClass and BusClass): reset behavior is dependent on the order
in which reset handlers are called. In particular doing external
side-effect (like setting an qemu_irq) is problematic because receiving
object may not be reset yet.
The Resettable interface divides the reset in 3 well defined phases.
To reset an object tree, all 1st phases are executed then all 2nd then
all 3rd. See the comments in include/hw/resettable.h for a more complete
description. The interface defines 3 phases to let the future
possibility of holding an object into reset for some time.
The qdev/qbus reset in DeviceClass and BusClass will be modified in
following commits to use this interface. A mechanism is provided
to allow executing a transitional reset handler in place of the 2nd
phase which is executed in children-then-parent order inside a tree.
This will allow to transition devices and buses smoothly while
keeping the exact current qdev/qbus reset behavior for now.
Documentation will be added in a following commit.
Signed-off-by: Damien Hedde <damien.hedde@greensocs.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20200123132823.1117486-4-damien.hedde@greensocs.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
