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Date:   Mon, 14 Sep 2020 14:14:52 -0700
From:   Matthias Kaehlcke <mka@chromium.org>
To:     Alan Stern <stern@rowland.harvard.edu>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Rob Herring <robh+dt@kernel.org>,
        Frank Rowand <frowand.list@gmail.com>,
        Krzysztof Kozlowski <krzk@kernel.org>,
        Bastien Nocera <hadess@hadess.net>,
        Ravi Chandra Sadineni <ravisadineni@chromium.org>,
        linux-usb@vger.kernel.org, Stephen Boyd <swboyd@chromium.org>,
        devicetree@vger.kernel.org,
        Douglas Anderson <dianders@chromium.org>,
        Peter Chen <peter.chen@nxp.com>, 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
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 <20200914201403.GA977844@rowland.harvard.edu>
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Hi Alan,

thanks for your feedback!

On Mon, Sep 14, 2020 at 04:14:03PM -0400, Alan Stern wrote:
> On Mon, Sep 14, 2020 at 11:27:49AM -0700, Matthias Kaehlcke wrote:
> > The main issue this driver addresses is that a USB hub needs to be
> > powered before it can be discovered. For onboard hubs this is often
> > solved by supplying the hub with an 'always-on' regulator, which is
> > kind of a hack. Some onboard hubs may require further initialization
> > steps, like changing the state of a GPIO or enabling a clock, which
> > requires further hacks. This driver creates a platform device
> > representing the hub which performs the necessary initialization.
> > Currently it only supports switching on a single regulator, support
> > for multiple regulators or other actions can be added as needed.
> > Different initialization sequences can be supported based on the
> > compatible string.
> > 
> > Besides performing the initialization the driver can be configured
> > to power the hub off during system suspend. This can help to extend
> > battery life on battery powered devices, which have no requirements
> > to keep the hub powered during suspend. The driver can also be
> > configured to leave the hub powered when a wakeup capable USB device
> > is connected when suspending, and keeping it powered otherwise.
> > 
> > Technically the driver consists of two drivers, the platform driver
> > described above and a very thin USB driver that subclasses the
> > generic hub driver.
> 
> Actually it subclasses the generic usb device driver, not the hub 
> driver.

ok, I'll change it in the next version.

> >  The purpose of this driver is to provide the
> > platform driver with the USB devices corresponding to the hub(s)
> > (a hub controller may provide multiple 'logical' hubs, e.g. one
> > to support USB 2.0 and another for USB 3.x).
> > 
> > Co-developed-by: Ravi Chandra Sadineni <ravisadineni@chromium.org>
> > Signed-off-by: Ravi Chandra Sadineni <ravisadineni@chromium.org>
> > Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
> > ---
> > This is an evolution of '[RFC] USB: misc: Add usb_hub_pwr driver'
> > (https://lore.kernel.org/patchwork/patch/1299239/).
> > 
> > Changes in v1:
> > - renamed the driver to 'onboard_usb_hub'
> > - single file for platform and USB driver
> > - USB hub devices register with the platform device
> >   - the DT includes a phandle of the platform device
> > - the platform device now controls when power is turned off
> > - the USB driver became a very thin subclass of the generic hub
> >   driver
> > - enabled autosuspend support
> 
> See https://marc.info/?l=linux-usb&m=159914635920888&w=2 and the 
> accompanying submissions.  You'll probably want to include those updates 
> in your driver.

Thanks for the pointer! I'll change the driver to use pm_ptr as suggested.