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

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Message-ID: <20150321013031.GC19849@shlinux2>
Date:	Sat, 21 Mar 2015 09:30:32 +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 Fri, Mar 20, 2015 at 01:08:25PM +0200, Roger Quadros wrote:
> On 20/03/15 11:46, Roger Quadros wrote:
> > On 20/03/15 09:18, Peter Chen wrote:
> >> 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.
> > 
> > Right. I mixed up into thinking that we should respect the softconnect
> > while in OTG mode. It seems that we should ignore it.
> > 
> >>
> >> 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).
> > 
> > Issuing SRP should be done by the otg-fsm and not udc-core.
> > The udc-core can at the least call usb_otg_kick_fsm() after setting the gadget
> > driver so that otg-fsm knows that we now have a valid gadget and can take
> > necessary action. i.e. change from b_idle to b_srp_init and then to b_peripheral.
> 
> To clarify further. Is it right to assume that OTG FSM will not be started till
> both gadget UDC driver _AND_ gadget function driver are loaded?
> 
> And it will be stopped when either of them unloads.
> 
> This simplifies things a lot.

Yes, you are right.

> 
> cheers,
> -roger
> 
> > 
> >>
> >> What is the "softconnect" used for? In otg fsm, we use b_bus_req for FSM.
> >>
> > I understand now that we shouldn't bother with softconnect when we are in OTG fsm mode.
> > That solves our problem with the running flags.
> > 
> > So now, b_peripheral == UDC_started.
> > 
> > I will address this in v2.
> > 
> > cheers,
> > -roger
> > --
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> > the body of a message to majordomo@...r.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> > 
> 

-- 

Best Regards,
Peter Chen
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