From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, James Hogan , Jiri Slaby , Tim Kryger , Ezequiel Garcia , Matt Porter , Markus Mayer , Heikki Krogerus , Wang Nan Subject: [PATCH 3.10 48/53] serial: 8250_dw: Fix LCR workaround regression Date: Mon, 7 Jul 2014 16:58:33 -0700 Message-Id: <20140707235830.740880485@linuxfoundation.org> In-Reply-To: <20140707235829.281783607@linuxfoundation.org> References: <20140707235829.281783607@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: 3.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: James Hogan 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(-) --- 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 uar 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 u 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));