linux-kernel - RE: PROBLEM: kernel oops with g

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Message-id: <002101c9f3e5$b4dc5a10$1e950e30$%szyprowski@samsung.com>
Date:	Tue, 23 Jun 2009 11:33:35 +0200
From:	Marek Szyprowski <m.szyprowski@...sung.com>
To:	'Alan Cox' <alan@...rguk.ukuu.org.uk>
Cc:	'David Brownell' <david-b@...bell.net>,
	'Alan Stern' <stern@...land.harvard.edu>,
	'Peter Korsgaard' <jacmet@...site.dk>,
	'USB list' <linux-usb@...r.kernel.org>,
	'Kernel development list' <linux-kernel@...r.kernel.org>,
	kyungmin.park@...sung.com
Subject: RE: PROBLEM: kernel oops with g_serial USB gadget on 2.6.30

Hello,

On Tuesday, June 23, 2009 11:21 AM, Alan Cox wrote:

> > that g_serial driver interacts with tty layer in that packet_done
> callback,
> > so this is the source of the problems. I noticed that some other UDC
> > drivers also does all its job from an interrupt, so they also might
> be
> > affected. How this bug should be properly resolved?
> 
> Either by not setting ->low_latency or by running the data paths from a
> non IRQ context.
> 
> Basically: don't set tty->low_latency if you are handling the
> processing
> from the IRQ path. The only case low_latency is useful is handling data
> from a non-IRQ path where you have latency concerns for tx/rx
> switching.

I know that, but I wonder how this should be handled in g_serial gadget
driver, which might be working on top of both types of low level
drivers (doing callback from irq or tasklet).

Are there any drawbacks of disabling low_latency mode if callbacks are
done from tasklet not from interrupt? If no then the low latency mode
should be disabled in g_serial driver.

Best regards
--
Marek Szyprowski
Samsung Poland R&D Center


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