This is a note to let you know that I've just added the patch titled
serial: core: Keep mctrl register state and cached copy in sync
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-core-keep-mctrl-register-state-and-cached-cop.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 148db6a691bf78d59ab2018e28749a0dac00a495
Author: Lukas Wunner <lukas@xxxxxxxxx>
Date: Sun Jan 2 18:52:44 2022 +0100
serial: core: Keep mctrl register state and cached copy in sync
[ Upstream commit 93a770b7e16772530196674ffc79bb13fa927dc6 ]
struct uart_port contains a cached copy of the Modem Control signals.
It is used to skip register writes in uart_update_mctrl() if the new
signal state equals the old signal state. It also avoids a register
read to obtain the current state of output signals.
When a uart_port is registered, uart_configure_port() changes signal
state but neglects to keep the cached copy in sync. That may cause
a subsequent register write to be incorrectly skipped. Fix it before
it trips somebody up.
This behavior has been present ever since the serial core was introduced
in 2002:
https://git.kernel.org/history/history/c/33c0d1b0c3eb
So far it was never an issue because the cached copy is initialized to 0
by kzalloc() and when uart_configure_port() is executed, at most DTR has
been set by uart_set_options() or sunsu_console_setup(). Therefore,
a stable designation seems unnecessary.
Signed-off-by: Lukas Wunner <lukas@xxxxxxxxx>
Link: https://lore.kernel.org/r/bceeaba030b028ed810272d55d5fc6f3656ddddb.1641129752.git.lukas@xxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 046bedca7b8f5..55108db5b64bf 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -2414,7 +2414,8 @@ uart_configure_port(struct uart_driver *drv, struct uart_state *state,
* We probably don't need a spinlock around this, but
*/
spin_lock_irqsave(&port->lock, flags);
- port->ops->set_mctrl(port, port->mctrl & TIOCM_DTR);
+ port->mctrl &= TIOCM_DTR;
+ port->ops->set_mctrl(port, port->mctrl);
spin_unlock_irqrestore(&port->lock, flags);
/*
