linux-kernel - RE: usb: gadget: f_fs: O_NONBLOCK waits MAX_SCHEDULE

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Date:	Tue, 2 Jun 2015 03:01:12 +0000
From:	Peter Chen <Peter.Chen@...escale.com>
To:	"Baxter, Jim" <jim_baxter@...tor.com>
CC:	Robert Baldyga <r.baldyga@...sung.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"Zapolskiy, Vladimir" <Vladimir_Zapolskiy@...tor.com>,
	"balbi@...com" <balbi@...com>
Subject: RE: usb: gadget: f_fs: O_NONBLOCK waits MAX_SCHEDULE_TIMEOUT

 
> >>>>
> >>>> Thank you, that sounds like the best approach.
> >>>> In this case I think perhaps the long wait without any data is an
> >>>> problem with the imx6 Chipidea USB controller.
> >>>
> >>> What's the possible problem?
> >>
> >> Sorry for the delay in replying, I have been getting some more
> >> details with a USB Analyser.
> >>
> >> The scenario is that the NCM  device is enumerating so we see the
> messages to:
> >>
> >> SetAddress (1)
> >> GetDescriptor (Device)
> >> GetDescriptor (StringN)
> >> GetDescriptor (Configuration)
> >> SetConfiguration (1)
> >> GetDescriptor (String iInterface)
> >> GetDescriptor (String iInterface)
> >>
> >> At this point the NCM host sends Writes to the F_FS EP0 but for some
> >> reason the host device does not respond and only issues SOF packets
> >> for hours. This happens occasionally and is fixed by turning the device off
> and on again.
> >>
> >>
> >
> > We may find this 'some reason', is it device error or host error?
> >
> > Do you have below patch in your code:
> >
> > commit 953c66469735aed8d2ada639a72b150f01dae605
> > Author: Abbas Raza <Abbas_Raza@...tor.com>
> > Date:   Thu Jul 17 19:34:31 2014 +0800
> >
> >     usb: chipidea: udc: Disable auto ZLP generation on ep0
> >
> >     There are 2 methods for ZLP (zero-length packet) generation:
> >     1) In software
> >     2) Automatic generation by device controller
> >
> >     1) is implemented in UDC driver and it attaches ZLP to IN packet if
> >        descriptor->size < wLength
> >     2) can be enabled/disabled by setting ZLT bit in the QH
> >
> > Peter
> 
> Yes I have that patch, could that be a problem?
> 

No, you need that patch.
Get to know which side has problem first.

Peter

> Jim
> 
> >
> >> Unless I am mistaken from a NCM gadget point of view the attached
> >> device is working correctly and there is no way to know it has failed, is that
> correct?
> >>
> >>>
> >>>>
> >>>> I guess it should suspend and drop the connections if there is no
> >>>> traffic for more than 10ms?
> >>>>
> >>>
> >>> If the Device side NAK host's IN/OUT token continually, the pipe
> >>> will not be stopped, the host will send token continually until the
> >>> application cancel this request.
> >>>
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