Re: [PATCH 2/3] doc: dt-binding: generic onboard USB HUB

From: Rob Herring <robh-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
To: Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org>
Cc: linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org,
	Philipp Zabel <p.zabel-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>,
	Peter Chen <peter.chen-KZfg59tc24xl57MIdRCFDg@public.gmane.org>,
	mark.rutland-5wv7dgnIgG8@public.gmane.org,
	devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	festevam-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org,
	pawel.moll-5wv7dgnIgG8@public.gmane.org,
	gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org,
	linux-usb-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	patryk-6+2coLtxvIyvnle+31E0rA@public.gmane.org,
	stern-nwvwT67g6+6dFdvTe/nMLpVzexx5G7lz@public.gmane.org,
	kernel-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org,
	shawnguo-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org
Subject: Re: [PATCH 2/3] doc: dt-binding: generic onboard USB HUB
Date: Tue, 8 Dec 2015 21:24:03 -0600	[thread overview]
Message-ID: <20151209032403.GA3716@rob-hp-laptop> (raw)
In-Reply-To: <19094869.VEiW4FjBL1@wuerfel>

On Tue, Dec 08, 2015 at 10:58:48AM +0100, Arnd Bergmann wrote:
> On Tuesday 08 December 2015 10:50:49 Philipp Zabel wrote:
> > Am Dienstag, den 08.12.2015, 09:37 +0800 schrieb Peter Chen:
> > > Add dt-binding documentation for generic onboard USB HUB.
> > > 
> > > Signed-off-by: Peter Chen <peter.chen-KZfg59tc24xl57MIdRCFDg@public.gmane.org>
> > > ---
> > >  .../bindings/usb/generic-onboard-hub.txt           | 28 ++++++++++++++++++++++
> > >  1 file changed, 28 insertions(+)
> > >  create mode 100644 Documentation/devicetree/bindings/usb/generic-onboard-hub.txt
> > > 
> > > diff --git a/Documentation/devicetree/bindings/usb/generic-onboard-hub.txt b/Documentation/devicetree/bindings/usb/generic-onboard-hub.txt
> > > new file mode 100644
> > > index 0000000..ea92205
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/usb/generic-onboard-hub.txt
> > > @@ -0,0 +1,28 @@
> > > +Generic Onboard USB HUB
> > >+
> > > +Required properties:
> > > +- compatible: should be "generic-onboard-hub"
> > 
> > This something we don't have to define ad-hoc. The hub hangs off an USB
> > controller, right? The "Open Firmware recommended practice: USB"
> > document already describes how to represent USB devices in a generic
> > manner:
> > http://www.firmware.org/1275/bindings/usb/usb-1_0.ps
> > 
> > Is there a reason not to reuse this?
> > 
> > The usb hub node would be a child of the usb controller node, and it
> > could use
> > 	compatible = "usb,class9"; /* bDeviceClass 9 (Hub) */
> 
> Good point, I had not thought of that when I looked at the patches.
>  
> Yes, let's do this way. I don't know if we ever implemented the simple
> patch to associate a USB device with a device_node, but if not, then
> let's do it now for this driver. A lot of people have asked for it in
> the past.

Agreed. Also, some hubs have I2C buses as well, but I still think under 
the USB bus is the right place.

However, one complication here is often (probably this case) these 
addtional signals need to be controlled before the device enumerates.

Rob
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