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

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Message-ID: <20150402002348.GA10964@shlinux2>
Date:	Thu, 2 Apr 2015 08:23:49 +0800
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

On Wed, Apr 01, 2015 at 06:29:05PM +0100, Baxter, Jim wrote:
> > 
> > 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?

> 
> 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.

-- 

Best Regards,
Peter Chen
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