linux-kernel - Re: [PATCH v5 1/4] dt-bindings: usb: Add binding for discrete onboard USB hubs

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Message-ID: <YDPsQNm95Zpm+cjl@google.com>
Date:   Mon, 22 Feb 2021 09:39:12 -0800
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Rob Herring <robh@...nel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Frank Rowand <frowand.list@...il.com>,
        devicetree@...r.kernel.org, Peter Chen <peter.chen@....com>,
        Stephen Boyd <swboyd@...omium.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Ravi Chandra Sadineni <ravisadineni@...omium.org>,
        Bastien Nocera <hadess@...ess.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Douglas Anderson <dianders@...omium.org>,
        Linux USB List <linux-usb@...r.kernel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>
Subject: Re: [PATCH v5 1/4] dt-bindings: usb: Add binding for discrete
 onboard USB hubs

On Fri, Feb 19, 2021 at 09:05:32AM -0600, Rob Herring wrote:
> On Wed, Feb 17, 2021 at 7:33 PM Matthias Kaehlcke <mka@...omium.org> wrote:
> >
> > Hi Rob,
> >
> > thanks for your review!
> >
> > On Wed, Feb 17, 2021 at 03:04:41PM -0600, Rob Herring wrote:
> > > On Wed, Feb 10, 2021 at 09:10:36AM -0800, Matthias Kaehlcke wrote:
> > > > Discrete onboard USB hubs (an example for such a hub is the Realtek
> > > > RTS5411) need to be powered and may require initialization of other
> > > > resources (like GPIOs or clocks) to work properly. This adds a device
> > > > tree binding for these hubs.
> > > >
> > > > Signed-off-by: Matthias Kaehlcke <mka@...omium.org>
> > > > ---
> > > >
> > > > Changes in v5:
> > > > - updated 'title'
> > > > - only use standard USB compatible strings
> > > > - deleted 'usb_hub' node
> > > > - renamed 'usb_controller' node to 'usb-controller'
> > > > - removed labels from USB nodes
> > > > - added 'vdd-supply' to USB nodes
> > > >
> > > > Changes in v4:
> > > > - none
> > > >
> > > > Changes in v3:
> > > > - updated commit message
> > > > - removed recursive reference to $self
> > > > - adjusted 'compatible' definition to support multiple entries
> > > > - changed USB controller phandle to be a node
> > > >
> > > > Changes in v2:
> > > > - removed 'wakeup-source' and 'power-off-in-suspend' properties
> > > > - consistently use spaces for indentation in example
> > > >
> > > >  .../bindings/usb/onboard_usb_hub.yaml         | 49 +++++++++++++++++++
> > > >  1 file changed, 49 insertions(+)
> > > >  create mode 100644 Documentation/devicetree/bindings/usb/onboard_usb_hub.yaml
> > > >
> > > > diff --git a/Documentation/devicetree/bindings/usb/onboard_usb_hub.yaml b/Documentation/devicetree/bindings/usb/onboard_usb_hub.yaml
> > > > new file mode 100644
> > > > index 000000000000..bf4ec52e6c7b
> > > > --- /dev/null
> > > > +++ b/Documentation/devicetree/bindings/usb/onboard_usb_hub.yaml
> > > > @@ -0,0 +1,49 @@
> > > > +# SPDX-License-Identifier: GPL-2.0-only or BSD-2-Clause
> > > > +%YAML 1.2
> > > > +---
> > > > +$id: http://devicetree.org/schemas/usb/onboard_usb_hub.yaml#
> > > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > > +
> > > > +title: Binding for discrete onboard USB hubs
> > >
> > > This isn't really generic. Maybe there's a set of hubs with only a
> > > single supply much like 'simple-panel', but I kind of doubt that here.
> > > There aren't hundreds of hub chips like panels. Though, we should put
> > > this into bindings/usb/hub/ so we start collecting hub bindings in one
> > > place.
> >
> > Ok, I agree that the name of the binding is too generic, I anticipated that
> > the power supply section would need to be extended to support other hub
> > chips.
> >
> > > A generic driver doesn't have to have a generic binding.
> >
> > That's a good point, it seems to make sense to have separate bindings in
> > this case.
> >
> > > You can have a specific device binding which is handled by a generic
> > > driver. Or not. Who knows. Maybe a simple user like u-boot has a generic
> > > driver while something more feature rich has a device specific binding.
> > >
> > > > +
> > > > +maintainers:
> > > > +  - Matthias Kaehlcke <mka@...omium.org>
> > >
> > > Now we have usb-device.yaml, you need:
> > >
> > > allOf:
> > >   - $ref: usb-device.yaml#
> >
> > ok
> >
> > So with your comments addressed it seems we have a binding that could be
> > acceptable. I'll still hold back a bit to see if we can make progress with
> > the discussion about using the 'graph' binding (https://lore.kernel.org/patchwork/patch/1379002/#1578294).
> > The one thing I don't like about the current binding is that it wouldn't
> > work out of the box with a hierarchy of hubs. To make that work on the
> > driver side an additional property would be needed to indicate that two
> > (or more) USB hub devices are related (i.e. are provided by the same
> > chip). This is needed to be able to decide whether the hub should be
> > powered down during system suspend.
> 
> How about a 'hub-companion' property or similar?

Yes, something like that is what I had in mind.

Another inconvenient is that collaboration from the controller /
generic hub driver is needed, however it seems at least Alan would be
ok with that.