diff options
| author | Lukas Wunner <lukas@wunner.de> | 2022-01-02 18:52:44 +0100 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2022-01-27 09:19:46 +0100 |
| commit | 8f6cecfff36ccd6a19fec2f6403abc3dcd870f8e (patch) | |
| tree | 284c95dc5897fff25cebc0a42ff5edff8cbd2af8 /drivers/tty | |
| parent | 6f7bd9f7c893363876722486a13d3b81ba524942 (diff) | |
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@wunner.de>
Link: https://lore.kernel.org/r/bceeaba030b028ed810272d55d5fc6f3656ddddb.1641129752.git.lukas@wunner.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Diffstat (limited to 'drivers/tty')
| -rw-r--r-- | drivers/tty/serial/serial_core.c | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c index aad640b9e3f4..c8a047ba76eb 100644 --- a/drivers/tty/serial/serial_core.c +++ b/drivers/tty/serial/serial_core.c @@ -2395,7 +2395,8 @@ 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); /* |