From: Matthias Kaehlcke <mka@chromium.org>
To: Peter Chen <peter.chen@nxp.com>
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
Date: Tue, 15 Sep 2020 16:03:45 -0700 [thread overview]
Message-ID: <20200915230345.GF2771744@google.com> (raw)
In-Reply-To: <AM7PR04MB715735A8A102F3EC9041EA328B200@AM7PR04MB7157.eurprd04.prod.outlook.com>
Hi Peter,
On Tue, Sep 15, 2020 at 07:05:38AM +0000, Peter Chen wrote:
>
> > > > + hub->cfg.power_off_in_suspend =
> > of_property_read_bool(dev->of_node, "power-off-in-suspend");
> > > > + hub->cfg.wakeup_source = 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?
> >
> > That would work for my use case, but I'm not sure it's a universally good
> > configuration.
> >
> > I don't have a specific USB device in mind, but you could have a device that
> > shouldn't lose it's context during suspend or keep operating autonomously (e.g.
> > a sensor with a large buffer collecting samples). Not sure if something like this
> > exists in the real though.
> >
> > 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 being
> > connected.
> >
>
> Whether or not it is a wakeup_source, it could get through its or its children's
> /sys/../power/wakeup value, you have already used usb_wakeup_enabled_descendants
> to know it.
I conceptually agree, but in practice there are some conflicting details:
wakeup for the hubs on my system is by default disabled, yet USB wakeup works
regardless, so the flag doesn't really provide useful information. I guess we
could still use it if there is no better way, but it doesn't seem ideal.
Similar for udev->bus->controller, according to sysfs it doesn't even have wakeup
support. Please let me know if there is a reliable way to check if wakeup is
enabled on the controller of a device.
> If the onboard HUB needs to reflect wakeup signal, it should not power off its regulator.
>
> For another property power-off-in-suspend, I think it is also a user option,
> but not a hardware feature.
Ok, I think you are suggesting a sysfs attribute instead of a DT property, that
sounds good to me.
next prev parent reply other threads:[~2020-09-15 23:04 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-14 18:27 [PATCH 1/2] dt-bindings: usb: Add binding for onboard USB hubs Matthias Kaehlcke
2020-09-14 18:27 ` [PATCH 2/2] USB: misc: Add onboard_usb_hub driver Matthias Kaehlcke
2020-09-14 19:52 ` Matthias Kaehlcke
2020-09-14 20:14 ` Alan Stern
2020-09-14 21:14 ` Matthias Kaehlcke
2020-09-15 2:55 ` Peter Chen
2020-09-15 5:02 ` Matthias Kaehlcke
2020-09-15 7:05 ` Peter Chen
2020-09-15 23:03 ` Matthias Kaehlcke [this message]
2020-09-16 2:14 ` Alan Stern
2020-09-16 19:27 ` Matthias Kaehlcke
2020-09-16 8:19 ` Peter Chen
2020-09-16 19:16 ` Matthias Kaehlcke
2020-09-17 0:27 ` Peter Chen
2020-09-17 0:47 ` Matthias Kaehlcke
2020-09-17 1:24 ` Peter Chen
2020-09-17 15:54 ` Matthias Kaehlcke
2020-09-15 14:21 ` [PATCH 1/2] dt-bindings: usb: Add binding for onboard USB hubs Rob Herring
2020-09-16 0:00 ` Matthias Kaehlcke
2020-09-18 16:05 ` Rob Herring
2020-09-22 23:39 ` Matthias Kaehlcke
2020-09-15 14:21 ` Rob Herring
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