From: Matthias Kaehlcke <mka@chromium.org>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: Doug Anderson <dianders@chromium.org>,
Rob Herring <robh@kernel.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Frank Rowand <frowand.list@gmail.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Linux USB List <linux-usb@vger.kernel.org>,
Bastien Nocera <hadess@hadess.net>,
Stephen Boyd <swboyd@chromium.org>,
Ravi Chandra Sadineni <ravisadineni@chromium.org>,
Krzysztof Kozlowski <krzk@kernel.org>,
"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS"
<devicetree@vger.kernel.org>, Peter Chen <peter.chen@nxp.com>
Subject: Re: [PATCH v4 1/2] dt-bindings: usb: Add binding for discrete onboard USB hubs
Date: Wed, 7 Oct 2020 10:28:47 -0700 [thread overview]
Message-ID: <20201007172847.GB620323@google.com> (raw)
In-Reply-To: <20201007163838.GA457977@rowland.harvard.edu>
On Wed, Oct 07, 2020 at 12:38:38PM -0400, Alan Stern wrote:
> On Wed, Oct 07, 2020 at 09:03:36AM -0700, Matthias Kaehlcke wrote:
> > On Tue, Oct 06, 2020 at 09:00:23PM -0400, Alan Stern wrote:
> > > On Tue, Oct 06, 2020 at 12:25:36PM -0700, Matthias Kaehlcke wrote:
> > > > On Tue, Oct 06, 2020 at 01:15:24PM -0400, Alan Stern wrote:
> > > > > You don't need a platform device or a new driver to do this. The code
> > > > > can go in the existing hub driver.
> > > >
> > > > Maybe. IIUC currently USB drivers don't support/use suspend_late. Could that
> > > > be added? It would simplify matters, otherwise all hubs need to know their
> > > > peers and check in suspend if they are the last hub standing, only then the
> > > > power can be switched off. It would be simpler if a single instance (e.g. the
> > > > hub with the DT entries) is in control.
> > >
> > > Adding suspend_late would be a little painful. But you don't really
> > > need it; you just need to make the "master" hub wait for its peer to
> > > suspend, which is easy to do.
> >
> > Ok, I wasn't sure if the hubs suspend asynchronously from each other. If they
> > do it should indeed not be a problem to have the "master" wait for its peers.
>
> Well, order of suspending is selectable by the user. It can be either
> asynchronous or reverse order of device registration, which might pose a
> problem. We don't know in advance which of two peer hubs will be
> registered first. It might be necessary to introduce some additional
> explicit synchronization.
I'm not sure we are understanding each other completely. I agree that
synchronization is needed to have the primary hub wait for its peers, that
was one of my initial concerns.
Lets use an example to clarify my secondary concern: a hub chip provides a
USB 3 and a USB 2 hub, lets say the USB 3 hub is the primary.
Here is some pseudo-code for the suspend function:
hub_suspend(hub)
...
if (hub->primary) {
device_pm_wait_for_dev(hub->peer)
// check for connected devices and turn regulator off
}
...
}
What I meant with 'asynchronous suspend' in this context:
Can hub_suspend() of the peer hub be executed (asynchronously) while the
primary is blocked on device_pm_wait_for_dev(), or would the primary wait
forever if the peer hub isn't suspended yet?
> > > And hubs would need to know their peers in any case, because you have to
> > > check if any devices attached to the peer have wakeup enabled.
> >
> > My concern was about all hubs (including 'secondaries') having to know their
> > peers and check on each other, in the scenario we are now talking about only
> > the "master" hub needs to know and check on its peers, which is fine.
>
> Not all hubs would need this. Only ones marked in DT as having a power
> regulator.
Sure, as long as the primary (with a power regulator) can wait for its peers
to suspend without the risk of blocking forever (my doubt above).
next prev parent reply other threads:[~2020-10-07 17:28 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-28 17:13 [PATCH v4 1/2] dt-bindings: usb: Add binding for discrete onboard USB hubs Matthias Kaehlcke
2020-09-28 17:13 ` [PATCH v4 2/2] USB: misc: Add onboard_usb_hub driver Matthias Kaehlcke
2020-09-28 18:47 ` Alan Stern
2020-09-29 1:43 ` Matthias Kaehlcke
2020-09-29 16:00 ` Alan Stern
2020-09-29 16:50 ` Matthias Kaehlcke
2020-09-28 22:03 ` Doug Anderson
2020-09-29 1:59 ` Matthias Kaehlcke
2020-09-28 22:13 ` [PATCH v4 1/2] dt-bindings: usb: Add binding for discrete onboard USB hubs Doug Anderson
2020-09-29 2:14 ` Matthias Kaehlcke
2020-09-29 20:17 ` Rob Herring
2020-09-29 22:09 ` Matthias Kaehlcke
2020-09-30 1:32 ` Alan Stern
2020-09-30 12:49 ` Matthias Kaehlcke
2020-09-30 14:44 ` Rob Herring
2020-09-30 15:28 ` Doug Anderson
2020-09-30 18:00 ` Doug Anderson
2020-09-30 19:19 ` Rob Herring
2020-10-01 21:39 ` Matthias Kaehlcke
2020-09-30 19:19 ` Alan Stern
2020-09-30 20:20 ` Rob Herring
2020-10-01 1:24 ` Alan Stern
2020-10-01 21:54 ` Matthias Kaehlcke
2020-10-02 1:21 ` Alan Stern
2020-10-02 16:08 ` Matthias Kaehlcke
2020-10-02 18:48 ` Alan Stern
2020-10-02 17:08 ` Doug Anderson
2020-10-02 18:36 ` Alan Stern
2020-10-02 22:58 ` Rob Herring
2020-10-03 12:41 ` Alan Stern
2020-10-05 16:06 ` Matthias Kaehlcke
2020-10-05 16:15 ` Alan Stern
2020-10-05 19:18 ` Matthias Kaehlcke
2020-10-05 19:36 ` Alan Stern
2020-10-05 19:59 ` Rob Herring
2020-10-05 23:29 ` Matthias Kaehlcke
2020-10-05 19:36 ` Rob Herring
2020-10-05 19:20 ` Rob Herring
2020-10-02 22:28 ` Rob Herring
2020-10-02 23:09 ` Doug Anderson
2020-10-06 0:45 ` Matthias Kaehlcke
2020-10-06 14:18 ` Alan Stern
2020-10-06 16:59 ` Matthias Kaehlcke
2020-10-06 17:15 ` Alan Stern
2020-10-06 19:25 ` Matthias Kaehlcke
2020-10-07 1:00 ` Alan Stern
2020-10-07 16:03 ` Matthias Kaehlcke
2020-10-07 16:38 ` Alan Stern
2020-10-07 17:28 ` Matthias Kaehlcke [this message]
2020-10-07 19:25 ` Alan Stern
2020-10-07 19:42 ` Matthias Kaehlcke
2020-10-07 20:17 ` Alan Stern
2020-10-07 21:42 ` Matthias Kaehlcke
2020-10-08 14:09 ` Alan Stern
2020-10-09 23:13 ` Matthias Kaehlcke
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