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serial: Test for no tx data on tx restart

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commit c557d392fb upstream.

Commit 717f3bbab3,
'serial_core: Fix conditional start_tx on ring buffer not empty'
exposes an incorrect assumption in several drivers' start_tx methods;
the tx ring buffer can, in fact, be empty when restarting tx while
performing flow control.

Affected drivers:
sunsab.c
ip22zilog.c
pmac_zilog.c
sunzilog.c
m32r_sio.c
imx.c

Other in-tree serial drivers either are not affected or already
test for empty tx ring buffer before transmitting.

Test for empty tx ring buffer in start_tx() method, after transmitting
x_char (if applicable).

Reported-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Cc: Seth Bollinger <sethb@digi.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Peter Hurley 2014-07-06 11:29:52 -04:00 • committed by Greg Kroah-Hartman
commit ba9286fc64
6 changed files with 18 additions and 3 deletions
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