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

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Date:	Mon, 25 May 2015 01:55:51 +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

 
> >>>
> >>> FunctionFS is very specific, because read/write operations are
> >>> directly translated into USB requests, which are asynchronous, so
> >>> you cannot use O_NONBLOCK.
> >>>
> >>> If you need non-blocking API you can use Asynchronous I/O (AIO). You
> >>> can find some examples in kernel sources (tools/usb/ffs-aio-example/).
> >>>
> >>> Br,
> >>> Robert Baldyga
> >>>
> >>
> >> 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

> 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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