linux-kernel - Re: [PATCH v8 13/14] usb: gadget: udc: adapt to OTG core

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Date:	Fri, 20 May 2016 10:26:03 +0300
From:	Roger Quadros <rogerq@...com>
To:	Peter Chen <hzpeterchen@...il.com>
CC:	<peter.chen@...escale.com>, <balbi@...nel.org>, <tony@...mide.com>,
	<gregkh@...uxfoundation.org>, <dan.j.williams@...el.com>,
	<mathias.nyman@...ux.intel.com>, <Joao.Pinto@...opsys.com>,
	<sergei.shtylyov@...entembedded.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 v8 13/14] usb: gadget: udc: adapt to OTG core

Peter,

On 20/05/16 04:39, Peter Chen wrote:
> On Wed, May 18, 2016 at 03:45:11PM +0300, Roger Quadros wrote:
>> On 18/05/16 06:18, Peter Chen wrote:
>>> On Mon, May 16, 2016 at 12:51:53PM +0300, Roger Quadros wrote:
>>>> On 16/05/16 12:23, Peter Chen wrote:
>>>>> On Mon, May 16, 2016 at 11:26:57AM +0300, Roger Quadros wrote:
>>>>>> Hi,
>>>>>>
>>>>>> On 16/05/16 10:02, Peter Chen wrote:
>>>>>>> On Fri, May 13, 2016 at 01:03:27PM +0300, Roger Quadros wrote:
>>>>>>>> +
>>>>>>>> +static int usb_gadget_connect_control(struct usb_gadget *gadget, bool connect)
>>>>>>>> +{
>>>>>>>> +	struct usb_udc *udc;
>>>>>>>> +
>>>>>>>> +	mutex_lock(&udc_lock);
>>>>>>>> +	udc = usb_gadget_to_udc(gadget);
>>>>>>>> +	if (!udc) {
>>>>>>>> +		dev_err(gadget->dev.parent, "%s: gadget not registered.\n",
>>>>>>>> +			__func__);
>>>>>>>> +		mutex_unlock(&udc_lock);
>>>>>>>> +		return -EINVAL;
>>>>>>>> +	}
>>>>>>>> +
>>>>>>>> +	if (connect) {
>>>>>>>> +		if (!gadget->connected)
>>>>>>>> +			usb_gadget_connect(udc->gadget);
>>>>>>>> +	} else {
>>>>>>>> +		if (gadget->connected) {
>>>>>>>> +			usb_gadget_disconnect(udc->gadget);
>>>>>>>> +			udc->driver->disconnect(udc->gadget);
>>>>>>>> +		}
>>>>>>>> +	}
>>>>>>>> +
>>>>>>>> +	mutex_unlock(&udc_lock);
>>>>>>>> +
>>>>>>>> +	return 0;
>>>>>>>> +}
>>>>>>>> +
>>>>>>>
>>>>>>> Since this is called for vbus interrupt, why not using
>>>>>>> usb_udc_vbus_handler directly, and call udc->driver->disconnect
>>>>>>> at usb_gadget_stop.
>>>>>>
>>>>>> We can't assume that this is always called for vbus interrupt so
>>>>>> I decided not to call usb_udc_vbus_handler.
>>>>>>
>>>>>> udc->vbus is really pointless for us. We keep vbus states in our
>>>>>> state machine and leave udc->vbus as ture always.
>>>>>>
>>>>>> Why do you want to move udc->driver->disconnect() to stop?
>>>>>> If USB controller disconnected from bus then the gadget driver
>>>>>> must be notified about the disconnect immediately. The controller
>>>>>> may or may not be stopped by the core.
>>>>>>
>>>>>
>>>>> Then, would you give some comments when this API will be used?
>>>>> I was assumed it is only used for drd state machine.
>>>>
>>>> drd_state machine didn't even need this API in the first place :).
>>>> You guys wanted me to separate out start/stop and connect/disconnect for full OTG case.
>>>> Won't full OTG state machine want to use this API? If not what would it use?
>>>>
>>>
>>> Oh, I meant only drd and fully otg state machine needs it. I am
>>> wondering if we need have a new API to do it. Two questions:
>>
>> OK.
>>>
>>> - Except for vbus interrupt, any chances this API will be used at
>>> current logic?
>>
>> I don't think so. But we can't assume caller behaviour for any API.
>>
>>> - When this API is called but without a coming gadget->stop?
>>>
>> Never for DRD case. But we want to catch wrong users.
>>
> 
> In future, otg_start_gadget will be used for both DRD and fully OTG FSM.
> There is no otg_loc_conn at current DRD FSM, but there is
> otg_loc_conn at current OTG FSM, see below.
> 
> DRD FSM:
> 	case OTG_STATE_B_IDLE:
> 		drd_set_protocol(fsm, PROTO_UNDEF);
> 		otg_drv_vbus(otg, 0);
> 		break;
> 	case OTG_STATE_B_PERIPHERAL:
> 		drd_set_protocol(fsm, PROTO_GADGET);
> 		otg_drv_vbus(otg, 0);
> 		break;
> 
> OTG FSM:
> 	case OTG_STATE_B_IDLE:
> 		otg_drv_vbus(otg, 0);
> 		otg_chrg_vbus(otg, 0);
> 		otg_loc_conn(otg, 0);
> 		otg_loc_sof(otg, 0);
> 		/*
> 		 * Driver is responsible for starting ADP probing
> 		 * if ADP sensing times out.
> 		 */
> 		otg_start_adp_sns(otg);
> 		otg_set_protocol(fsm, PROTO_UNDEF);
> 		otg_add_timer(otg, B_SE0_SRP);
> 		break;
> 	case OTG_STATE_B_PERIPHERAL:
> 		otg_chrg_vbus(otg, 0);
> 		otg_loc_sof(otg, 0);
> 		otg_set_protocol(fsm, PROTO_GADGET);
> 		otg_loc_conn(otg, 1);
> 		break;
> 
> My original suggestion is to have an API to do pull dp and this API
> will be used at both DRD and OTG FSM, and called at otg_loc_conn.

The API is usb_gadget_connect_control();

> The (de)initialize is the same for both two FSMs, it both includes
> init peripheral mode and pull up dp, and can be done by drd_set_protocol(fsm, PROTO_GADGET)
> otg_loc_conn(otg, 1);
> 
> What do you think?
> 

I think loc_conn is a bit confusing to drd users. Another issue I see is that 
DRD controller drivers will need to explicitly pass .loc_conn ops via the otg_fsm_ops.
This is an additional step and totally unnecessary as it can be automatically done
via direct DRD -> UDC-core call.

cheers,
-roger