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

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Date:   Mon, 14 Sep 2020 16:14:03 -0400
From:   Alan Stern <stern@...land.harvard.edu>
To:     Matthias Kaehlcke <mka@...omium.org>
Cc:     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, Stephen Boyd <swboyd@...omium.org>,
        devicetree@...r.kernel.org,
        Douglas Anderson <dianders@...omium.org>,
        Peter Chen <peter.chen@....com>, 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 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.

>  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@...omium.org>
> Signed-off-by: Ravi Chandra Sadineni <ravisadineni@...omium.org>
> Signed-off-by: Matthias Kaehlcke <mka@...omium.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.

Alan Stern