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

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Message-ID: <20200917155403.GA21107@google.com>
Date:   Thu, 17 Sep 2020 08:54:03 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Peter Chen <peter.chen@....com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Alan Stern <stern@...land.harvard.edu>,
        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 Thu, Sep 17, 2020 at 01:24:30AM +0000, Peter Chen wrote:
> > > >
> > >
> > > You may need both (glue & xhci), it depends on system design, and
> > > usually, these two kinds of wakeup setting isn't conflict.
> > 
> > Ok, thanks. So if I understand correctly the onboard hub driver should check the
> > wakeup state of the xHCI to determine if remote wakeup is enabled for the
> > controller (after all it doesn't know anything about the platform device).
> > Wakeup might not work properly if it is disabled for the platform device, but it's
> > the responsability of the board software/config to make sure it is enabled
> > (possibly this could be done by making the dwc3-qcom driver understand the
> > 'wakeup-source' property, as the xhci-mtk driver does).
> 
> No, every level should handle its own wakeup setting. You may have to do this since the USB bus and platform bus
> are two different buses, you should not visit device structure across the bus. And you don't need a device tree property
> to do it. For platform driver, you could use device_may_wakeup, for onboard hub power driver, you could use
> usb_wakeup_enabled_descendants since you need to cover descendants.
> 
> The purpose of these two wakeup logic is different, for USB bus, it is used to tell USB devices to enable remote wakeup
> and do not power off its regulator; for platform bus, it is used to tell the controller to enable its wakeup setting and keep
> the regulator for its USB controller and USB PHY (if needed).

Sorry, I didn't express myself clearly. With the platform device I was
referring to the dwc3-qcom ('glue') in this case, which could check
it's own 'wakeup-source' attribute to enable wakeup at boot. The driver
currently enables wakeup statically. The onboard_hub driver is agnostic
of this device.