linux-kernel - Re: [PATCH v9 08/14] usb: otg: add OTG/dual-role core

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Date:	Sun, 12 Jun 2016 14:26:17 +0800
From:	Peter Chen <hzpeterchen@...il.com>
To:	Roger Quadros <rogerq@...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 v9 08/14] usb: otg: add OTG/dual-role core

On Thu, Jun 09, 2016 at 10:24:44AM +0300, Roger Quadros wrote:
> On 08/06/16 15:42, Peter Chen wrote:
> > On Wed, Jun 08, 2016 at 01:12:10PM +0300, Roger Quadros wrote:
> >> Hi,
> >>
> >> On 08/06/16 12:53, Peter Chen wrote:
> >>> On Wed, Jun 08, 2016 at 12:03:40PM +0300, Roger Quadros wrote:
> >>>> +int usb_otg_unregister(struct device *dev)
> >>>> +{
> >>>> +	struct usb_otg *otg;
> >>>> +
> >>>> +	mutex_lock(&otg_list_mutex);
> >>>> +	otg = usb_otg_get_data(dev);
> >>>> +	if (!otg) {
> >>>> +		dev_err(dev, "otg: %s: device not in otg list\n",
> >>>> +			__func__);
> >>>> +		mutex_unlock(&otg_list_mutex);
> >>>> +		return -EINVAL;
> >>>> +	}
> >>>> +
> >>>> +	/* prevent unregister till both host & gadget have unregistered */
> >>>> +	if (otg->host || otg->gadget) {
> >>>> +		dev_err(dev, "otg: %s: host/gadget still registered\n",
> >>>> +			__func__);
> >>>
> >>> You need to call mutex_unlock here
> >>
> >> Indeed. good catch.
> >>>
> >>>> +
> >>>> +int usb_otg_gadget_ready(struct usb_gadget *gadget, bool ready)
> >>>> +{
> >>>
> >>> What this API is for? Why need it in this version?
> >>
> >> we moved gadget to otg registration from udc_bind_to_driver() to usb_add_gadget_udc_release().
> >> This means there is a window when gadget function driver (e.g. g_zero) is not loaded.
> >> We don't want to start the gadget controller in that window.
> >>
> >> usb_otg_gadget_ready() is used by gadget core to notify the otg core when the function driver
> >> is ready or not-ready.
> >>
> > 
> > Why you need to move this from gadget's probe to udc's probe? Currently,
> > the sequence of gadget and udc's probe is random, but udc_bind_to_driver
> > is called when udc is ready.
> > 
> Because we need to support -EPROBE_DEFER at udc probe.
> At udc_bind_to_driver there is no scope for -EPROBE_DEFER.
> 

Why udc_bind_to_driver can't return -EPROBE_DEFER if register to OTG is
failed?

> Another issue is that we need to register with otg and have otg->caps available
> before driver->bind() is called in udc_bind_to_driver(). Else gadget function
> will not have the correct OTG descriptor.
> 

You can do register before calling driver->bind.

-- 

Best Regards,
Peter Chen