linux-kernel - Re: [PATCH v3 00/11] USB: OTG/DRD Core functionality

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Date:	Mon, 13 Jul 2015 12:14:43 -0700
From:	Andrew Bresticker <abrestic@...omium.org>
To:	Roger Quadros <rogerq@...com>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Felipe Balbi <balbi@...com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	peter.chen@...escale.com, Dan Williams <dan.j.williams@...el.com>,
	jun.li@...escale.com,
	Mathias Nyman <mathias.nyman@...ux.intel.com>,
	tony@...mide.com, Joao.Pinto@...opsys.com,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-omap@...r.kernel.org,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH v3 00/11] USB: OTG/DRD Core functionality

Hi Roger,

On Wed, Jul 8, 2015 at 3:19 AM, Roger Quadros <rogerq@...com> wrote:
> Usage model:
> -----------
>
> - The OTG controller device is assumed to be the parent of
> the host and gadget controller. It must call usb_otg_register()
> before populating the host and gadget devices so that the OTG
> core is aware that it is an OTG device before the host & gadget
> register. The OTG controller must provide struct otg_fsm_ops *
> which will be called by the OTG core depending on OTG bus state.

I'm wondering if the requirement that the OTG controller be the parent
of the USB host/device-controllers makes sense.  For some context, I'm
working on adding dual-role support for Tegra210, specifically on a
system with USB Type-C.  On Tegra, the USB host-controller and USB
device-controller are two separate IP blocks (XUSB host and XUSB
device) with another, separate, IP block (XUSB padctl) for the USB PHY
and OTG support.  In the non-Type-C case, your OTG framework could
work well, though it's debatable as to whether or not the XUSB padctl
device should be a parent to the XUSB host/device-controller devices
(currently it isn't - it's just a PHY provider).  But in the Type-C
case, it's an off-chip embedded controller that determines the
dual-role status of the Type-C port, so the above requirement doesn't
make sense at all.

My idea was to have the OTG/DRD controller explicitly specify its host
and device controllers, so in DT, something like:

otg-controller {
    ...
    device-controller = <&usb_device>;
    host-controller = <&usb_host>;
    ...
};

usb_device: usb-device@.... {
    ...
};

usb_host: usb-host@... {
    ...
};

What do you think?

Thanks,
Andrew
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