This is a note to let you know that I've just added the patch titled
serial: imx: fix tx statemachine deadlock
to the 5.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
serial-imx-fix-tx-statemachine-deadlock.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit d0da713c70c7edb12411cdc5dc55aee1c8dc0706
Author: Paul Geurts <paul_geurts@xxxxxxx>
Date: Fri Nov 24 14:11:10 2023 +0100
serial: imx: fix tx statemachine deadlock
[ Upstream commit 78d60dae9a0c9f09aa3d6477c94047df2fe6f7b0 ]
When using the serial port as RS485 port, the tx statemachine is used to
control the RTS pin to drive the RS485 transceiver TX_EN pin. When the
TTY port is closed in the middle of a transmission (for instance during
userland application crash), imx_uart_shutdown disables the interface
and disables the Transmission Complete interrupt. afer that,
imx_uart_stop_tx bails on an incomplete transmission, to be retriggered
by the TC interrupt. This interrupt is disabled and therefore the tx
statemachine never transitions out of SEND. The statemachine is in
deadlock now, and the TX_EN remains low, making the interface useless.
imx_uart_stop_tx now checks for incomplete transmission AND whether TC
interrupts are enabled before bailing to be retriggered. This makes sure
the state machine handling is reached, and is properly set to
WAIT_AFTER_SEND.
Fixes: cb1a60923609 ("serial: imx: implement rts delaying for rs485")
Signed-off-by: Paul Geurts <paul_geurts@xxxxxxx>
Tested-by: Rasmus Villemoes <rasmus.villemoes@xxxxxxxxx>
Tested-by: Eberhard Stoll <eberhard.stoll@xxxxxx>
Link: https://lore.kernel.org/r/AM0PR09MB26758F651BC1B742EB45775995B8A@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index f236e4738b78..8bb7d5b5de9d 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -461,13 +461,13 @@ static void imx_uart_stop_tx(struct uart_port *port)
ucr1 = imx_uart_readl(sport, UCR1);
imx_uart_writel(sport, ucr1 & ~UCR1_TRDYEN, UCR1);
+ ucr4 = imx_uart_readl(sport, UCR4);
usr2 = imx_uart_readl(sport, USR2);
- if (!(usr2 & USR2_TXDC)) {
+ if ((!(usr2 & USR2_TXDC)) && (ucr4 & UCR4_TCEN)) {
/* The shifter is still busy, so retry once TC triggers */
return;
}
- ucr4 = imx_uart_readl(sport, UCR4);
ucr4 &= ~UCR4_TCEN;
imx_uart_writel(sport, ucr4, UCR4);
