linux-kernel - Re: [RFC][PATCH 2/9] usb: gadget: add usb_gadget

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Date:	Fri, 20 Mar 2015 15:18:19 +0800
From:	Peter Chen <peter.chen@...escale.com>
To:	Roger Quadros <rogerq@...com>
CC:	Li Jun <b47624@...escale.com>, <gregkh@...uxfoundation.org>,
	<balbi@...com>, <stern@...land.harvard.edu>,
	<dan.j.williams@...el.com>, <jun.li@...escale.com>,
	<mathias.nyman@...ux.intel.com>, <linux-usb@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linux-omap@...r.kernel.org>
Subject: Re: [RFC][PATCH 2/9] usb: gadget: add usb_gadget_start/stop()

On Thu, Mar 19, 2015 at 04:50:31PM +0200, Roger Quadros wrote:
> On 19/03/15 16:09, Li Jun wrote:
> > On Thu, Mar 19, 2015 at 12:14:39PM +0200, Roger Quadros wrote:
> >> On 19/03/15 05:30, Peter Chen wrote:
> >>> On Wed, Mar 18, 2015 at 03:55:56PM +0200, Roger Quadros wrote:
> >>>> The OTG state machine needs a mechanism to start and
> >>>> stop the gadget controller. Add usb_gadget_start()
> >>>> and usb_gadget_stop().
> >>>>
> >>>> Signed-off-by: Roger Quadros <rogerq@...com>
> >>>> ---
> >>>>  drivers/usb/gadget/udc/udc-core.c | 166 +++++++++++++++++++++++++++++++++++---
> >>>>  include/linux/usb/gadget.h        |   3 +
> >>>>  2 files changed, 158 insertions(+), 11 deletions(-)
> >>>>
> >>>> diff --git a/drivers/usb/gadget/udc/udc-core.c b/drivers/usb/gadget/udc/udc-core.c
> >>>> index 5a81cb0..69b4123 100644
> >>>> --- a/drivers/usb/gadget/udc/udc-core.c
> >>>> +++ b/drivers/usb/gadget/udc/udc-core.c
> >>>> @@ -35,6 +35,8 @@
> >>>>   * @dev - the child device to the actual controller
> >>>>   * @gadget - the gadget. For use by the class code
> >>>>   * @list - for use by the udc class driver
> >>>> + * @running - udc is running
> >>>
> >>> Doesn't OTG FSM should know it?
> >>
> >> Not really, as the gadget driver might not have been loaded yet or userspace might
> >> have disabled softconnect when the OTG FSM wants UDC to start.
> >>
> >> So only UDC knows if it has really started or not based on this flag.
> >>
> > 
> > why this can not be known by check the otg fsm state? i.e. if the device in
> > b_peripheral or a_peripheral state, udc should had started, isn't it?
> 
> If gadget function driver (which is different from UDC driver) is not yet loaded
> then we can't start UDC even if otg fsm is in b_peripheral.
> Also, if userspace has disabled softconnect we can't start UDC.
> 
> So, b_peripheral != UDC_started.
> 
> I've tried to address this issue by adding the checks in usb_gadget_start().
> 

Ok, maybe we have different understanding for 'B-Device' at software,
In spec, it says the Micro-AB receptacle with nothing connected can be
'B-Device', but in fact, we may not enable device mode before loading
gadget driver, in chipidea fsm design, if the gadget driver is not
loaded, the FSM will not start, and it is at OTG_STATE_UNDEFINED.

One more thing is we may need to find a place to issue SRP when we
load gadget driver, since we may at b_idle  at that time due to host
closes the vbus (timeout for a_wait_bcon).

What is the "softconnect" used for? In otg fsm, we use b_bus_req for FSM.

-- 

Best Regards,
Peter Chen
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