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authorLukas Wunner <lukas@wunner.de>2022-01-02 18:52:44 +0100
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2022-01-06 16:01:48 +0100
commit93a770b7e16772530196674ffc79bb13fa927dc6 (patch)
treef1bb8b416901fbd28906e3347b40c3f539b9713e /drivers
parent195437d14fb424a2ee50d51441181f16fd549789 (diff)
downloadlinux-93a770b7e16772530196674ffc79bb13fa927dc6.tar.bz2
serial: core: Keep mctrl register state and cached copy in sync
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@wunner.de> Link: https://lore.kernel.org/r/bceeaba030b028ed810272d55d5fc6f3656ddddb.1641129752.git.lukas@wunner.de Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers')
-rw-r--r--drivers/tty/serial/serial_core.c3
1 files changed, 2 insertions, 1 deletions
diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 259f28ec6c8b..dc40c4155356 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -2389,7 +2389,8 @@ 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);
/*