linux-kernel - Re: [PATCH v17 1/7] usb: misc: Add onboard_usb

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Message-ID: <Yc4T1qSkcRF2iBVg@google.com>
Date:   Thu, 30 Dec 2021 12:17:26 -0800
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Mathias Nyman <mathias.nyman@...el.com>,
        Felipe Balbi <balbi@...nel.org>, linux-kernel@...r.kernel.org,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Peter Chen <peter.chen@...nel.org>, linux-usb@...r.kernel.org,
        devicetree@...r.kernel.org,
        Douglas Anderson <dianders@...omium.org>,
        Roger Quadros <rogerq@...nel.org>,
        Michal Simek <michal.simek@...inx.com>,
        Ravi Chandra Sadineni <ravisadineni@...omium.org>,
        Bastien Nocera <hadess@...ess.net>
Subject: Re: [PATCH v17 1/7] usb: misc: Add onboard_usb_hub driver

On Mon, Dec 20, 2021 at 11:05:28PM +0300, Dmitry Osipenko wrote:
> 16.11.2021 23:07, Matthias Kaehlcke пишет:
> > +static const struct usb_device_id onboard_hub_id_table[] = {
> > +	{ USB_DEVICE(VENDOR_ID_REALTEK, 0x0411) }, /* RTS0411 USB 3.0 */
> > +	{ USB_DEVICE(VENDOR_ID_REALTEK, 0x5411) }, /* RTS5411 USB 2.0 */
> > +	{},
> > +};
> 
> RTS5411 two times in the comments?

One time, the other is RTS0511

> Internet suggests that RTS5411 is USB 3.0

Correct, however the chip internally has two hubs, one for USB2 and one for
USB3:

  Bus 002 Device 002: ID 0bda:0411 Realtek Semiconductor Corp. 4-Port USB 3.1 Hub
  Bus 001 Device 002: ID 0bda:5411 Realtek Semiconductor Corp. 4-Port USB 2.1 Hub

> Are these hubs expected to be powered-on only when upstream port is
> enabled? Shouldn't runtime PM be used for that somehow?

In the general case I would expect that a onboard hub is connected to a port
that is enabled. For now I think it's fine to power the hub always when the
system is running (which is also the current situation with using always-on
regulators). If someone has an actual use case where the upstream port can
be disabled they can add support for that later.