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

[Greg KH <gregkh@linuxfoundation.org>]

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