On Wed 26 Aug 2020 at 10:14, Philipp Zabel <p.zabel@xxxxxxxxxxxxxx> wrote: > On Tue, 2020-08-25 at 16:20 +0200, Jerome Brunet wrote: >> On Tue 25 Aug 2020 at 12:20, Philipp Zabel <p.zabel@xxxxxxxxxxxxxx> wrote: >> >> > On Mon, 2020-08-24 at 16:26 +0200, Jerome Brunet wrote: >> > [...] >> > > In practice, I think your proposition would work since the drivers >> > > sharing this USB reset line are likely to be probed/suspended/resumed at >> > > the same time but ... >> > > >> > > If we imagine a situation where 2 device share a reset line, 1 go in >> > > suspend, the other does not - if the first device as control of the >> > > reset, it could trigger it and break the 2nd device. Same goes for >> > > probe/remove() >> > > >> > > I agree it could be seen as unlikely but leaving such race condition >> > > open looks dangerous to me. >> > >> > You are right, this is not good enough. >> > >> > > > Is this something that would be feasible for your combination of >> > > > drivers? Otherwise it is be unclear to me under which condition a driver >> > > > should be allowed to call the proposed reset_control_clear(). >> > > >> > > I was thinking of reset_control_clear() as the counter part of >> > > reset_control_reset(). >> > >> > I'm not particularly fond of reset_control_clear as a name, because it >> > is very close to "clearing a reset bit" which usually would deassert a >> > reset line (or the inverse). >> >> It was merely a suggestion :) any other name you prefer is fine by me > > Naming is hard. All metaphors I can think of are either a obscure or > clash with other current usage. My instinct would be to call this > "resetting the (reset) control", but _reset() is already taken, with the > opposite meaning. How about _rewind() or _rearm()? Not sure if those are > good metaphors either, but at least there is no obvious but incorrect > interpretation. I kind of wish reset_control_reset() would be called > reset_control_trigger() instead. We'll pick something for the v1 ... maybe the inspiration will come later on and we'll make a v2 ;) > >> > > When a reset_control_reset() has been called once, "triggered_count" is >> > > incremented which signals that the ressource under the reset is >> > > "in_use" and the reset should not be done again. >> > >> > "triggered_count" would then have to be renamed to something like >> > "trigger_requested_count", or "use_count". I wonder it might be possible >> > to merge this with "deassert_count" as they'd share the same semantics >> > (while the count is > 0, the reset line must stay deasserted). >> >> Sure. Could investigate this as a 2nd step ? > > Yes. > >> I'd like to bring a solution for our meson-usb use case quickly - even >> with the revert suggested, we are having an ugly warning around suspend > > I understand. Let's still do this carefully :) will do > >> > > 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)? >> >> I'm not Martin but these devices are the origin of the request/suggestion. > > So these two phy drivers are used together with dwc3-meson-g12a? Yes, reset is shared by the different usb devices of the SoCs > Will you change them to use the new API as well? That's the plan, yes. > > regards > Philipp
