linux-kernel - RE: [PATCH v6 09/12] usb: gadget: udc: adapt to OTG core

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Date:	Tue, 26 Apr 2016 00:07:00 +0000
From:	Jun Li <jun.li@....com>
To:	Roger Quadros <rogerq@...com>,
	"stern@...land.harvard.edu" <stern@...land.harvard.edu>,
	"balbi@...nel.org" <balbi@...nel.org>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"peter.chen@...escale.com" <peter.chen@...escale.com>
CC:	"dan.j.williams@...el.com" <dan.j.williams@...el.com>,
	"jun.li@...escale.com" <jun.li@...escale.com>,
	"mathias.nyman@...ux.intel.com" <mathias.nyman@...ux.intel.com>,
	"tony@...mide.com" <tony@...mide.com>,
	"Joao.Pinto@...opsys.com" <Joao.Pinto@...opsys.com>,
	"abrestic@...omium.org" <abrestic@...omium.org>,
	"r.baldyga@...sung.com" <r.baldyga@...sung.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-omap@...r.kernel.org>
Subject: RE: [PATCH v6 09/12] usb: gadget: udc: adapt to OTG core

Hi

> -----Original Message-----
> From: Roger Quadros [mailto:rogerq@...com]
> Sent: Monday, April 25, 2016 10:04 PM
> To: Jun Li <jun.li@....com>; stern@...land.harvard.edu; balbi@...nel.org;
> gregkh@...uxfoundation.org; peter.chen@...escale.com
> Cc: dan.j.williams@...el.com; jun.li@...escale.com;
> mathias.nyman@...ux.intel.com; tony@...mide.com; Joao.Pinto@...opsys.com;
> abrestic@...omium.org; r.baldyga@...sung.com; linux-usb@...r.kernel.org;
> linux-kernel@...r.kernel.org; linux-omap@...r.kernel.org
> Subject: Re: [PATCH v6 09/12] usb: gadget: udc: adapt to OTG core
> 
> Hi,
> 
> On 21/04/16 09:38, Jun Li wrote:
> > Hi,
> >
> > ...
> >>
> >>  /**
> >> + * usb_gadget_start - start the usb gadget controller and connect to
> >> +bus
> >> + * @gadget: the gadget device to start
> >> + *
> >> + * This is external API for use by OTG core.
> >> + *
> >> + * Start the usb device controller and connect to bus (enable pull).
> >> + */
> >> +static int usb_gadget_start(struct usb_gadget *gadget) {
> >> +	int ret;
> >> +	struct usb_udc *udc = NULL;
> >> +
> >> +	dev_dbg(&gadget->dev, "%s\n", __func__);
> >> +	mutex_lock(&udc_lock);
> >> +	list_for_each_entry(udc, &udc_list, list)
> >> +		if (udc->gadget == gadget)
> >> +			goto found;
> >> +
> >> +	dev_err(gadget->dev.parent, "%s: gadget not registered.\n",
> >> +		__func__);
> >> +	mutex_unlock(&udc_lock);
> >> +	return -EINVAL;
> >> +
> >> +found:
> >> +	ret = usb_gadget_udc_start(udc);
> >> +	if (ret)
> >> +		dev_err(&udc->dev, "USB Device Controller didn't start: %d\n",
> >> +			ret);
> >> +	else
> >> +		usb_udc_connect_control(udc);
> >
> > For drd, it's fine, but for real otg, gadget connect should be done by
> > loc_conn() instead of gadget start.
> 
> It is upto the OTG state machine to call gadget_start() when it needs to
> connect to the bus (i.e. loc_conn()). I see no point in calling gadget
> start before.
> 
> Do you see any issue in doing so?

This is what OTG state machine does:
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;

You intend to abstract something common in this api when start gadget,
which should be called by otg_set_protocol(fsm, PROTO_GADGET); and
drd_set_protocol(fsm, PROTO_GADGET); right?

So you may move usb_udc_connect_control(IMO usb_gadget_connect()
is better)out of usb_gadget_start(), then for drd:

case OTG_STATE_B_PERIPHERAL:
     drd_set_protocol(fsm, PROTO_GADGET);
     otg_drv_vbus(otg, 0);
     usb_gadget_connect();

Li Jun

> 
> cheers,
> -roger
> 
> >
> >> +
> >> +	mutex_unlock(&udc_lock);
> >> +
> >> +	return ret;
> >> +}
> >> +
> >> +/**
> >> + * usb_gadget_stop - disconnect from bus and stop the usb gadget
> >> + * @gadget: The gadget device we want to stop
> >> + *
> >> + * This is external API for use by OTG core.
> >> + *
> >> + * Disconnect from the bus (disable pull) and stop the
> >> + * gadget controller.
> >> + */
> >> +static int usb_gadget_stop(struct usb_gadget *gadget) {
> >> +	struct usb_udc *udc = NULL;
> >> +
> >> +	dev_dbg(&gadget->dev, "%s\n", __func__);
> >> +	mutex_lock(&udc_lock);
> >> +	list_for_each_entry(udc, &udc_list, list)
> >> +		if (udc->gadget == gadget)
> >> +			goto found;
> >> +
> >> +	dev_err(gadget->dev.parent, "%s: gadget not registered.\n",
> >> +		__func__);
> >> +	mutex_unlock(&udc_lock);
> >> +	return -EINVAL;
> >> +
> >> +found:
> >> +	usb_gadget_disconnect(udc->gadget);
> >
> > Likewise, gadget disconnect also should be done by loc_conn() instead
> > of gadget stop.
> >
> >> +	udc->driver->disconnect(udc->gadget);
> >> +	usb_gadget_udc_stop(udc);
> >> +	mutex_unlock(&udc_lock);
> >> +
> >> +	return 0;
> >> +}
> >> +
> >
> > Li Jun
> >