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From:   Peter Chen <peter.chen@nxp.com>
To:     Matthias Kaehlcke <mka@chromium.org>
CC:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Rob Herring <robh+dt@kernel.org>,
        Frank Rowand <frowand.list@gmail.com>,
        Alan Stern <stern@rowland.harvard.edu>,
        Krzysztof Kozlowski <krzk@kernel.org>,
        Bastien Nocera <hadess@hadess.net>,
        Ravi Chandra Sadineni <ravisadineni@chromium.org>,
        "linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>,
        Stephen Boyd <swboyd@chromium.org>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        Douglas Anderson <dianders@chromium.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "Alexander A. Klimov" <grandmaster@al2klimov.de>,
        Masahiro Yamada <masahiroy@kernel.org>
Subject: Re: [PATCH 2/2] USB: misc: Add onboard_usb_hub driver
Thread-Topic: [PATCH 2/2] USB: misc: Add onboard_usb_hub driver
Thread-Index: AQHWisa8s1Sayn6UyUeJIx1ZNmduw6lpAX4AgAAjrICAAB3x4IABEESAgACa9IA=
Date:   Wed, 16 Sep 2020 08:19:07 +0000
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On 20-09-15 16:03:45, Matthias Kaehlcke wrote:
> Hi Peter,
>=20
> On Tue, Sep 15, 2020 at 07:05:38AM +0000, Peter Chen wrote:
> >  =20
> > > > > +	hub->cfg.power_off_in_suspend =3D
> > > of_property_read_bool(dev->of_node, "power-off-in-suspend");
> > > > > +	hub->cfg.wakeup_source =3D of_property_read_bool(dev->of_node,
> > > > > +"wakeup-source");
> > > >
> > > > Do you really need these two properties? If the device (and its
> > > > children if existed) has wakeup enabled, you keep power in suspend,
> > > > otherwise, you could close it, any exceptions?
> > >=20
> > > That would work for my use case, but I'm not sure it's a universally =
good
> > > configuration.
> > >=20
> > > I don't have a specific USB device in mind, but you could have a devi=
ce that
> > > shouldn't lose it's context during suspend or keep operating autonomo=
usly (e.g.
> > > a sensor with a large buffer collecting samples). Not sure if somethi=
ng like this
> > > exists in the real though.
> > >=20
> > > I'm not an expert, but it seems there are USB controllers with wakeup=
 support
> > > which is always enabled. A board with such a controller then couldn't=
 have a
> > > policy to power down the hub regardless of wakeup capable devices bei=
ng
> > > connected.
> > >=20
> >=20
> > Whether or not it is a wakeup_source, it could get through its or its c=
hildren's
> > /sys/../power/wakeup value, you have already used usb_wakeup_enabled_de=
scendants
> > to know it.
>=20
> I conceptually agree, but in practice there are some conflicting details:
>=20
> wakeup for the hubs on my system is by default disabled, yet USB wakeup w=
orks
> regardless, so the flag doesn't really provide useful information. I gues=
s we
> could still use it if there is no better way, but it doesn't seem ideal.
>=20
> Similar for udev->bus->controller, according to sysfs it doesn't even hav=
e wakeup
> support. Please let me know if there is a reliable way to check if wakeup=
 is
> enabled on the controller of a device.

Then, how could your code work, you use usb_wakeup_enabled_descendants
to get if HUB or the descendants under the HUB has wakeup enabled?

If you use dwc3, you need to enable xhci-plat.c's wakeup entry if your
system needs xHCI connect/disconnect wakeup event. I have one pending
patch to do it:

https://www.spinics.net/lists/linux-usb/msg199406.html

>=20
> > If the onboard HUB needs to reflect wakeup signal, it should not power =
off its regulator.
> >=20
> > For another property power-off-in-suspend, I think it is also a user op=
tion,
> > but not a hardware feature.
>=20
> Ok, I think you are suggesting a sysfs attribute instead of a DT property=
, that
> sounds good to me.

Yes.

--=20

Thanks,
Peter Chen=