From d791a3e3ebce3b1f91381bbe2eee5224612b7d51 Mon Sep 17 00:00:00 2001 From: James Hogan Date: Tue, 10 Dec 2013 22:28:04 +0000 Subject: [PATCH] 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 Cc: Greg Kroah-Hartman Cc: Jiri Slaby Cc: Tim Kryger Cc: Ezequiel Garcia Cc: Matt Porter Cc: Markus Mayer Tested-by: Tim Kryger Tested-by: Ezequiel Garcia Tested-by: Heikki Krogerus Cc: Wang Nan Signed-off-by: Greg Kroah-Hartman --- 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 1b55923..345b5dd 100644 --- a/drivers/tty/serial/8250/8250_dw.c +++ b/drivers/tty/serial/8250/8250_dw.c @@ -92,7 +92,8 @@ 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)); @@ -121,7 +122,8 @@ 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)); -- 2.7.4