linux-kernel - Re: [PATCH 2/2] USB: misc: Add onboard_usb

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Message-ID: <20200916021421.GA1024554@rowland.harvard.edu>
Date:   Tue, 15 Sep 2020 22:14:21 -0400
From:   Alan Stern <stern@...land.harvard.edu>
To:     Matthias Kaehlcke <mka@...omium.org>
Cc:     Peter Chen <peter.chen@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Bastien Nocera <hadess@...ess.net>,
        Ravi Chandra Sadineni <ravisadineni@...omium.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        Stephen Boyd <swboyd@...omium.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Douglas Anderson <dianders@...omium.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Alexander A. Klimov" <grandmaster@...klimov.de>,
        Masahiro Yamada <masahiroy@...nel.org>
Subject: Re: [PATCH 2/2] USB: misc: Add onboard_usb_hub driver

On Tue, Sep 15, 2020 at 04:03:45PM -0700, Matthias Kaehlcke wrote:
> Hi Peter,
> 
> On Tue, Sep 15, 2020 at 07:05:38AM +0000, Peter Chen wrote:

> > 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.

The wakeup setting for USB hubs affects only the following events: port 
connect, port disconnect, and port overcurrent.  It does not refer to 
forwarding wakeup requests from downstream USB devices; that is always 
enabled.  So maybe your wakeup flag really is accurate and you didn't 
realize it.

> 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.

The host controller's sysfs wakeup setting should always be correct.  If 
it isn't, that indicates there is a bug in the host controller driver or 
the corresponding platform-specific code.  What driver does your system 
use?

Alan Stern