From: Lukas Wunner lukas@wunner.de
commit 2dd8a74fddd21b95dcc60a2d3c9eaec993419d69 upstream.
RTS polarity of rs485-enabled ports is currently initialized on uart open via:
tty_port_open() tty_port_block_til_ready() tty_port_raise_dtr_rts() # if (C_BAUD(tty)) uart_dtr_rts() uart_port_dtr_rts()
There's at least three problems here:
First, if no baud rate is set, RTS polarity is not initialized. That's the right thing to do for rs232, but not for rs485, which requires that RTS is deasserted unconditionally.
Second, if the DeviceTree property "linux,rs485-enabled-at-boot-time" is present, RTS should be deasserted as early as possible, i.e. on probe. Otherwise it may remain asserted until first open.
Third, even though RTS is deasserted on open and close, it may subsequently be asserted by uart_throttle(), uart_unthrottle() or uart_set_termios() because those functions aren't rs485-aware. (Only uart_tiocmset() is.)
To address these issues, move RTS initialization from uart_port_dtr_rts() to uart_configure_port(). Prevent subsequent modification of RTS polarity by moving the existing rs485 check from uart_tiocmget() to uart_update_mctrl().
That way, RTS is initialized on probe and then remains unmodified unless the uart transmits data. If rs485 is enabled at runtime (instead of at boot) through a TIOCSRS485 ioctl(), RTS is initialized by the uart driver's ->rs485_config() callback and then likewise remains unmodified.
The PL011 driver initializes RTS on uart open and prevents subsequent modification in its ->set_mctrl() callback. That code is obsoleted by the present commit, so drop it.
Cc: Jan Kiszka jan.kiszka@siemens.com Cc: Su Bao Cheng baocheng.su@siemens.com Signed-off-by: Lukas Wunner lukas@wunner.de Link: https://lore.kernel.org/r/2d2acaf3a69e89b7bf687c912022b11fd29dfa1e.164290928... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/tty/serial/serial_core.c | 34 ++++++++++++---------------------- 1 file changed, 12 insertions(+), 22 deletions(-)
--- a/drivers/tty/serial/serial_core.c +++ b/drivers/tty/serial/serial_core.c @@ -144,6 +144,11 @@ uart_update_mctrl(struct uart_port *port unsigned long flags; unsigned int old;
+ if (port->rs485.flags & SER_RS485_ENABLED) { + set &= ~TIOCM_RTS; + clear &= ~TIOCM_RTS; + } + spin_lock_irqsave(&port->lock, flags); old = port->mctrl; port->mctrl = (old & ~clear) | set; @@ -157,23 +162,10 @@ uart_update_mctrl(struct uart_port *port
static void uart_port_dtr_rts(struct uart_port *uport, int raise) { - int rs485_on = uport->rs485_config && - (uport->rs485.flags & SER_RS485_ENABLED); - int RTS_after_send = !!(uport->rs485.flags & SER_RS485_RTS_AFTER_SEND); - - if (raise) { - if (rs485_on && RTS_after_send) { - uart_set_mctrl(uport, TIOCM_DTR); - uart_clear_mctrl(uport, TIOCM_RTS); - } else { - uart_set_mctrl(uport, TIOCM_DTR | TIOCM_RTS); - } - } else { - unsigned int clear = TIOCM_DTR; - - clear |= (!rs485_on || RTS_after_send) ? TIOCM_RTS : 0; - uart_clear_mctrl(uport, clear); - } + if (raise) + uart_set_mctrl(uport, TIOCM_DTR | TIOCM_RTS); + else + uart_clear_mctrl(uport, TIOCM_DTR | TIOCM_RTS); }
/* @@ -1116,11 +1108,6 @@ uart_tiocmset(struct tty_struct *tty, un goto out;
if (!tty_io_error(tty)) { - if (uport->rs485.flags & SER_RS485_ENABLED) { - set &= ~TIOCM_RTS; - clear &= ~TIOCM_RTS; - } - uart_update_mctrl(uport, set, clear); ret = 0; } @@ -2429,6 +2416,9 @@ uart_configure_port(struct uart_driver * */ spin_lock_irqsave(&port->lock, flags); port->mctrl &= TIOCM_DTR; + if (port->rs485.flags & SER_RS485_ENABLED && + !(port->rs485.flags & SER_RS485_RTS_AFTER_SEND)) + port->mctrl |= TIOCM_RTS; port->ops->set_mctrl(port, port->mctrl); spin_unlock_irqrestore(&port->lock, flags);