linux-kernel - Re: [PATCH v10 08/14] usb: otg: add OTG/dual-role core

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Date:	Fri, 10 Jun 2016 13:54:52 +0300
From:	Roger Quadros <rogerq@...com>
To:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
	<peter.chen@...escale.com>
CC:	<balbi@...nel.org>, <tony@...mide.com>,
	<gregkh@...uxfoundation.org>, <dan.j.williams@...el.com>,
	<mathias.nyman@...ux.intel.com>, <Joao.Pinto@...opsys.com>,
	<jun.li@...escale.com>, <grygorii.strashko@...com>,
	<yoshihiro.shimoda.uh@...esas.com>, <robh@...nel.org>,
	<nsekhar@...com>, <b-liu@...com>, <linux-usb@...r.kernel.org>,
	<linux-omap@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<devicetree@...r.kernel.org>
Subject: Re: [PATCH v10 08/14] usb: otg: add OTG/dual-role core

On 10/06/16 13:44, Sergei Shtylyov wrote:
> On 6/10/2016 1:19 PM, Roger Quadros wrote:
> 
>>>> It provides APIs for the following tasks
>>>>
>>>> - Registering an OTG/dual-role capable controller
>>>> - Registering Host and Gadget controllers to OTG core
>>>> - Providing inputs to and kicking the OTG state machine
>>>>
>>>> Provide a dual-role device (DRD) state machine.
>>>> DRD mode is a reduced functionality OTG mode. In this mode
>>>> we don't support SRP, HNP and dynamic role-swap.
>>>>
>>>> In DRD operation, the controller mode (Host or Peripheral)
>>>> is decided based on the ID pin status. Once a cable plug (Type-A
>>>> or Type-B) is attached the controller selects the state
>>>> and doesn't change till the cable in unplugged and a different
>>>> cable type is inserted.
>>>>
>>>> As we don't need most of the complex OTG states and OTG timers
>>>> we implement a lean DRD state machine in usb-otg.c.
>>>> The DRD state machine is only interested in 2 hardware inputs
>>>> 'id' and 'b_sess_vld'.
>>>>
>>>> Signed-off-by: Roger Quadros <rogerq@...com>
>>>
>>
>> <snip>
>>
>>> [...]
>>>> +/**
>>>> + * usb_otg_register_gadget - Register the gadget controller to OTG core
>>>> + * @gadget:    gadget controller
>>>
>>>    We call that USB device controller (UDC). I'm not sure what you meant here...
>>>    And what about the 2nd arg, 'ops'?
>>
>> There are 2 data structures representing the Device controller.
>>
>> struct usb_gadget - represents a usb slave device
>> struct usb_udc -struct usb_udc - describes one usb device controller
>>
>> usb_udc is for private use only. usb_otg_register_gadget() takes struct usb_gadget
>> as argument.
>>
>> Do you want me to refer to struct usb_gadget as UDC?
> 
>    No.
> 
>> What is wrong with calling it gadget controller?
> 
>    It's not a controller, it's a piece of software AFAIU. Or is my English just too weak? :-)

Everything at this point is a piece of software :).

struct usb_gadget, represents the gadget controller device not the driver (or software).

struct usb_gadget_driver represents the gadget function driver.
struct usb_gadget_ops represents the UDC driver ops.

--
cheers,
-roger