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

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Date:	Fri, 10 Jun 2016 13:44:03 +0300
From:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:	Roger Quadros <rogerq@...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 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? :-)

> --
> cheers,
> -roger

MBR, Sergei