serial: imx: fix cached UCR2 read on software reset

To reset the UART the SRST needs be cleared (low active). According
to the documentation the bit will remain active for 4 module clocks
until it is cleared (set to 1).

Hence the real register need to be read in case the cached register
indicates that the SRST bit is zero.

This bug lead to wrong baudrate because the baud rate register got
restored before reset completed in imx_flush_buffer.

Fixes: 3a0ab62f43de ("serial: imx: implement shadow registers for UCRx and UFCR")
Signed-off-by: Stefan Agner <stefan@agner.ch>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Reviewed-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 65d7a2bfb6d2aaaebe83b60a1e2a18d9167e31e5..c2fc6bef7a6f28a6fc3fe9f18782c555bdb35a35 100644 (file)
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -316,7 +316,7 @@ static u32 imx_uart_readl(struct imx_port *sport, u32 offset)
                 * differ from the value that was last written. As it only
                 * clears after being set, reread conditionally.
                 */
-               if (sport->ucr2 & UCR2_SRST)
+               if (!(sport->ucr2 & UCR2_SRST))
                        sport->ucr2 = readl(sport->port.membase + offset);
                return sport->ucr2;
                break;