[3.11.y.z extended stable] Patch "serial: 8250_dw: Fix LCR workaround regression" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    serial: 8250_dw: Fix LCR workaround regression

to the linux-3.11.y-queue branch of the 3.11.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.11.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.11.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From e5472b518e20b7671dd9e0e3475e6ca38152d3ea Mon Sep 17 00:00:00 2001
From: James Hogan <james.hogan at imgtec.com>
Date: Tue, 10 Dec 2013 22:28:04 +0000
Subject: serial: 8250_dw: Fix LCR workaround regression

commit 6979f8d28049879e6147767d93ba6732c8bd94f4 upstream.

Commit c49436b657d0 (serial: 8250_dw: Improve unwritable LCR workaround)
caused a regression. It added a check that the LCR was written properly
to detect and workaround the busy quirk, but the behaviour of bit 5
(UART_LCR_SPAR) differs between IP versions 3.00a and 3.14c per the
docs. On older versions this caused the check to fail and it would
repeatedly force idle and rewrite the LCR register, causing delays and
preventing any input from serial being received.

This is fixed by masking out UART_LCR_SPAR before making the comparison.

Signed-off-by: James Hogan <james.hogan at imgtec.com>
Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Cc: Jiri Slaby <jslaby at suse.cz>
Cc: Tim Kryger <tim.kryger at linaro.org>
Cc: Ezequiel Garcia <ezequiel.garcia at free-electrons.com>
Cc: Matt Porter <matt.porter at linaro.org>
Cc: Markus Mayer <markus.mayer at linaro.org>
Tested-by: Tim Kryger <tim.kryger at linaro.org>
Tested-by: Ezequiel Garcia <ezequiel.garcia at free-electrons.com>
Tested-by: Heikki Krogerus <heikki.krogerus at linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Cc: Wang Nan <wangnan0 at huawei.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/tty/serial/8250/8250_dw.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
index 1dec9af3c9ab..70ecf541b77a 100644
--- a/drivers/tty/serial/8250/8250_dw.c
+++ b/drivers/tty/serial/8250/8250_dw.c
@@ -95,7 +95,8 @@ static void dw8250_serial_out(struct uart_port *p, int offset, int value)
 	if (offset == UART_LCR) {
 		int tries = 1000;
 		while (tries--) {
-			if (value == p->serial_in(p, UART_LCR))
+			unsigned int lcr = p->serial_in(p, UART_LCR);
+			if ((value & ~UART_LCR_SPAR) == (lcr & ~UART_LCR_SPAR))
 				return;
 			dw8250_force_idle(p);
 			writeb(value, p->membase + (UART_LCR << p->regshift));
@@ -131,7 +132,8 @@ static void dw8250_serial_out32(struct uart_port *p, int offset, int value)
 	if (offset == UART_LCR) {
 		int tries = 1000;
 		while (tries--) {
-			if (value == p->serial_in(p, UART_LCR))
+			unsigned int lcr = p->serial_in(p, UART_LCR);
+			if ((value & ~UART_LCR_SPAR) == (lcr & ~UART_LCR_SPAR))
 				return;
 			dw8250_force_idle(p);
 			writel(value, p->membase + (UART_LCR << p->regshift));
--
1.9.1