[PATCH 1/1] usb: dwc3: meson-g12a: fix shared reset control use

[Martin Blumenstingl]

Hi Philipp,

On Tue, Aug 25, 2020 at 12:20 PM Philipp Zabel <p.zabel at pengutronix.de> wrote:
[...]
> > reset_control_clear()
> > would be the way to state that the ressource is no longer used and, that
> > from the caller perspective, the reset can fired again if necessary.
> >
> > If we take the probe / suspend / resume example:
> > * 1st device using the shared will actually trigger it (as it is now)
> > * following device just increase triggered_count
> >
> > If all devices go to suspend (calling reset_control_clear()) then
> > triggered_count will reach zero, allowing the first device resuming to
> > trigger the reset again ... this is important since it might not be the
> > one which would have got the exclusive control
> >
> > If any device don't go to suspend, meaning the ressource under reset
> > keep on being used, no reset will performed. With exlusive control,
> > there is a risk that the resuming device resets something already in use.
> >
> > Regarding the condition, on shared resets, call reset_control_reset()
> > should be balanced reset_control_clear() - no clear before reset.
>
> Martin, is this something that would be useful for the current users of
> the shared reset trigger functionality (phy-meson-gxl-usb2 and phy-
> meson8b-usb2 with reset-meson)?
for the specific use-case (system suspend) this would currently not be
useful for the two drivers you have named. This is because the
platforms on which they are used currently don't support system
suspend.
if other drivers are going to benefit from this change then please go
ahead and add the necessary API. Then I can also use it in these
drivers. however, (as far as I understand) I won't be able to verify
the new "fixed" behavior


Best regards,
Martin