linux-kernel - Re: ftdi_sio: fix status line change handling for TIOCMIWAIT and TIOCGICOUNT

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Date:	Mon, 26 Mar 2012 13:31:23 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Simon Arlott <simon@...e.lp0.eu>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Uwe Bonnes <bon@...ktron.ikp.physik.tu-darmstadt.de>,
	USB list <linux-usb@...r.kernel.org>
Subject: Re: ftdi_sio: fix status line change handling for TIOCMIWAIT and
 TIOCGICOUNT

On Mon, Mar 26, 2012 at 09:19:40PM +0100, Simon Arlott wrote:
> Handling of TIOCMIWAIT was changed by commit 1d749f9afa657f6ee9336b2bc1fcd750a647d157
>  USB: ftdi_sio.c: Use ftdi async_icount structure for TIOCMIWAIT, as in other drivers
> 
> FTDI_STATUS_B0_MASK does not indicate the changed modem status lines,
> it indicates the value of the current modem status lines. An xor is
> still required to determine which lines have changed.
> 
> The count was only being incremented if the line was high. The only
> reason TIOCMIWAIT still worked was because the status packet is
> repeated every 1ms, so the count was always changing. The wakeup
> itself still ran based on the status lines changing.
> 
> This change fixes handling of updates to the modem status lines and
> allows multiple processes to use TIOCMIWAIT concurrently.
> 
> Tested with two processes waiting on different status lines being
> toggled independently.

Nice, do you happen to have the source for such a test tool anywhere
around?  I'd like to use it for future testing if at all possible.

I'll queue this up after 3.4-rc1 is out.

greg k-h
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