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

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Date:	Tue, 14 Jul 2015 11:18:30 -0700
From:	Andrew Bresticker <abrestic@...omium.org>
To:	Peter Chen <peter.chen@...escale.com>
Cc:	Roger Quadros <rogerq@...com>,
	Alan Stern <stern@...land.harvard.edu>,
	Felipe Balbi <balbi@...com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	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 Peter,

On Mon, Jul 13, 2015 at 5:59 PM, Peter Chen <peter.chen@...escale.com> wrote:
> On Mon, Jul 13, 2015 at 12:14:43PM -0700, Andrew Bresticker wrote:
>> 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.
>
> Hi Andrew,
>
> I think your problem is how to add your core driver to manage device and
> host functionality together, and once you find how (through padctl/type-c
> controller) to do it based on current code, it will be clear how to use roger
> proposal framework at that time.
>
> Most of current core drivers, we use extcon driver (through gpio) or USB
> vbus/id pin (through internal registers) to manager roles.

Right, currently I'm modeling the Type-C controller as an extcon
device and handle the role-changes in the core drivers, but that
doesn't really make sense for the non-Type-C case where we use the
XUSB padctl controller and need a full OTG state-machine.  Roger's new
OTG/DRD framework would fit my situation perfectly since it makes the
host/device-controller drivers independent from all the
OTG/role-changing logic.  The only issue is the requirement that the
OTG/DRD controller be the parent device of the host/device
controllers.

Thanks,
Andrew
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