From: Philipp Zabel <p.zabel@pengutronix.de>
To: Jerome Brunet <jbrunet@baylibre.com>,
Dan Robertson <dan@dlrobertson.com>,
Martin Blumenstingl <martin.blumenstingl@googlemail.com>,
Neil Armstrong <narmstrong@baylibre.com>,
Kevin Hilman <khilman@baylibre.com>
Cc: linux-amlogic@lists.infradead.org, linux-usb@vger.kernel.org,
aouledameur@baylibre.com, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 1/1] usb: dwc3: meson-g12a: fix shared reset control use
Date: Wed, 26 Aug 2020 10:14:31 +0200 [thread overview]
Message-ID: <79a2e84548697be86be3d8fde4a1975ab37d0c00.camel@pengutronix.de> (raw)
In-Reply-To: <1j5z964xis.fsf@starbuckisacylon.baylibre.com>
On Tue, 2020-08-25 at 16:20 +0200, Jerome Brunet wrote:
> On Tue 25 Aug 2020 at 12:20, Philipp Zabel <p.zabel@pengutronix.de> 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.
> > > 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 :)
> > > 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?
Will you change them to use the new API as well?
regards
Philipp
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next prev parent reply other threads:[~2020-08-26 8:14 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-13 16:05 [PATCH 0/1] usb: dwc3: meson-g12a: fix shared reset control use Dan Robertson
2020-07-13 16:05 ` [PATCH 1/1] " Dan Robertson
2020-07-18 8:47 ` Neil Armstrong
2020-07-18 22:57 ` Dan Robertson
2020-08-19 15:03 ` Jerome Brunet
2020-08-20 18:02 ` Kevin Hilman
2020-08-20 18:27 ` Jerome Brunet
2020-08-20 18:49 ` Kevin Hilman
2020-08-20 18:44 ` Dan Robertson
2020-08-24 8:14 ` Jerome Brunet
2020-08-24 10:24 ` Philipp Zabel
2020-08-24 14:26 ` Jerome Brunet
2020-08-25 10:20 ` Philipp Zabel
2020-08-25 14:20 ` Jerome Brunet
2020-08-26 8:14 ` Philipp Zabel [this message]
2020-08-26 8:34 ` Jerome Brunet
2020-08-29 15:25 ` Martin Blumenstingl
2020-09-02 14:13 ` Amjad Ouled-Ameur
2020-09-07 8:31 ` Jerome Brunet
2020-09-07 8:33 ` Amjad Ouled-Ameur
2020-07-14 6:56 ` [PATCH 0/1] " Anand Moon
2020-07-14 13:30 ` Dan Robertson
2020-07-14 15:27 ` Anand Moon
2020-07-15 2:58 ` Dan Robertson
2020-07-15 16:23 ` Anand Moon
2020-07-17 9:01 ` Anand Moon
2020-07-17 16:38 ` Anand Moon
2020-07-18 6:31 ` Anand Moon
2020-07-18 8:46 ` Neil Armstrong
2020-07-18 9:54 ` Anand Moon
2020-08-17 17:48 ` patchwork-bot+linux-amlogic
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