linux-kernel - RE: [PATCH v6 07/12] usb: otg: add OTG/dual-role core

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Date:	Tue, 26 Apr 2016 07:00:22 +0000
From:	Jun Li <jun.li@....com>
To:	Peter Chen <hzpeterchen@...il.com>
CC:	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>,
	"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 07/12] usb: otg: add OTG/dual-role core

Hi

> -----Original Message-----
> From: Peter Chen [mailto:hzpeterchen@...il.com]
> Sent: Tuesday, April 26, 2016 2:28 PM
> To: Jun Li <jun.li@....com>
> Cc: Roger Quadros <rogerq@...com>; stern@...land.harvard.edu;
> balbi@...nel.org; gregkh@...uxfoundation.org; peter.chen@...escale.com;
> 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 07/12] usb: otg: add OTG/dual-role core
> 
> On Tue, Apr 26, 2016 at 05:11:36AM +0000, Jun Li wrote:
> > Hi
> >
> > > -----Original Message-----
> > > From: Peter Chen [mailto:hzpeterchen@...il.com]
> > > Sent: Tuesday, April 26, 2016 11:47 AM
> > > To: Jun Li <jun.li@....com>
> > > Cc: Roger Quadros <rogerq@...com>; stern@...land.harvard.edu;
> > > balbi@...nel.org; gregkh@...uxfoundation.org;
> > > peter.chen@...escale.com; 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 07/12] usb: otg: add OTG/dual-role core
> > >
> > > On Tue, Apr 26, 2016 at 02:07:56AM +0000, Jun Li wrote:
> > > > > +struct usb_otg *usb_otg_register(struct device *dev,
> > > > > +				 struct usb_otg_config *config) {
> > > > > +	struct usb_otg *otg;
> > > > > +	struct otg_wait_data *wait;
> > > > > +	int ret = 0;
> > > > > +
> > > > > +	if (!dev || !config || !config->fsm_ops)
> > > > > +		return ERR_PTR(-EINVAL);
> > > > > +
> > > > > +	/* already in list? */
> > > > > +	mutex_lock(&otg_list_mutex);
> > > > > +	if (usb_otg_get_data(dev)) {
> > > > > +		dev_err(dev, "otg: %s: device already in otg list\n",
> > > > > +			__func__);
> > > > > +		ret = -EINVAL;
> > > > > +		goto unlock;
> > > > > +	}
> > > > > +
> > > > > +	/* allocate and add to list */
> > > > > +	otg = kzalloc(sizeof(*otg), GFP_KERNEL);
> > > > > +	if (!otg) {
> > > > > +		ret = -ENOMEM;
> > > > > +		goto unlock;
> > > > > +	}
> > > > > +
> > > > > +	otg->dev = dev;
> > > > > +	otg->caps = config->otg_caps;
> > > > > +
> > > > > +	if ((otg->caps->hnp_support || otg->caps->srp_support ||
> > > > > +	     otg->caps->adp_support) && !config->otg_work)
> > > > > +		dev_info(dev, "otg: limiting to dual-role\n");
> > > >
> > > > dev_err, this should be an error.
> > >
> > > The condition may be wrong, but it is an information to show that
> > > current OTG is dual-role.
> >
> > This should not happen in any correct design, I even doubt if we
> > should try to continue by "downgrade" it to be duel role, currently
> > the only example user is dual role, so doing like this can't be tested
> > by real case, this downgrade is not so easy like we image, at least
> > for chipidea otg driver, simply replace a queue worker may not work,
> > as we have much more difference between the 2 configs.
> >
> 
> Would you show more why chipidea can't work just replace the work item,
> and see if anything we still can improve for this framework?

In real OTG, we need enable AVV irq, but for duel role, nobody care/handle,
there are much more resource required for OTG: timers, hnp polling,
otg test device handling... 

with current design, chipidea driver can support real OTG with its own
queue worker, or DRD with Roger's drd work item if config is correct.

But improve something to work on a *wrong* config will make it complicated
and does not make much sense IMO.

Li Jun
> 
> --
> Best Regards,
> Peter Chen