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authorSherry Sun <sherry.sun@nxp.com>2024-03-05 09:57:06 +0800
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2024-03-05 13:40:07 +0000
commit74cb7e0355fae9641f825afa389d3fba3b617714 (patch)
tree4ef2c5d7ddbb37b0b2010b8f1c06ef74ee0f9a8e
parent1581dafaf0d34bc9c428a794a22110d7046d186d (diff)
tty: serial: fsl_lpuart: avoid idle preamble pending if CTS is enabled
If the remote uart device is not connected or not enabled after booting up, the CTS line is high by default. At this time, if we enable the flow control when opening the device(for example, using “stty -F /dev/ttyLP4 crtscts” command), there will be a pending idle preamble(first writing 0 and then writing 1 to UARTCTRL_TE will queue an idle preamble) that cannot be sent out, resulting in the uart port fail to close(waiting for TX empty), so the user space stty will have to wait for a long time or forever. This is an LPUART IP bug(idle preamble has higher priority than CTS), here add a workaround patch to enable TX CTS after enabling UARTCTRL_TE, so that the idle preamble does not get stuck due to CTS is deasserted. Fixes: 380c966c093e ("tty: serial: fsl_lpuart: add 32-bit register interface support") Cc: stable <stable@kernel.org> Signed-off-by: Sherry Sun <sherry.sun@nxp.com> Reviewed-by: Alexander Sverdlin <alexander.sverdlin@siemens.com> Link: https://lore.kernel.org/r/20240305015706.1050769-1-sherry.sun@nxp.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--drivers/tty/serial/fsl_lpuart.c7
1 files changed, 5 insertions, 2 deletions
diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c
index 5ddf110aedbe..bbcbc91482af 100644
--- a/drivers/tty/serial/fsl_lpuart.c
+++ b/drivers/tty/serial/fsl_lpuart.c
@@ -2345,9 +2345,12 @@ lpuart32_set_termios(struct uart_port *port, struct ktermios *termios,
lpuart32_write(&sport->port, bd, UARTBAUD);
lpuart32_serial_setbrg(sport, baud);
- lpuart32_write(&sport->port, modem, UARTMODIR);
- lpuart32_write(&sport->port, ctrl, UARTCTRL);
+ /* disable CTS before enabling UARTCTRL_TE to avoid pending idle preamble */
+ lpuart32_write(&sport->port, modem & ~UARTMODIR_TXCTSE, UARTMODIR);
/* restore control register */
+ lpuart32_write(&sport->port, ctrl, UARTCTRL);
+ /* re-enable the CTS if needed */
+ lpuart32_write(&sport->port, modem, UARTMODIR);
if ((ctrl & (UARTCTRL_PE | UARTCTRL_M)) == UARTCTRL_PE)
sport->is_cs7 = true;