serial: Deassert Transmit Enable on probe in driver-specific way

When a UART port is newly registered, uart_configure_port() seeks to
deassert RS485 Transmit Enable by setting the RTS bit in port->mctrl.
However a number of UART drivers interpret a set RTS bit as *assertion*
instead of deassertion:  Affected drivers include those using
serial8250_em485_config() (except 8250_bcm2835aux.c) and some using
mctrl_gpio (e.g. imx.c).

Since the interpretation of the RTS bit is driver-specific, it is not
suitable as a means to centrally deassert Transmit Enable in the serial
core.  Instead, the serial core must call on drivers to deassert it in
their driver-specific way.  One way to achieve that is to call
->rs485_config().  It implicitly deasserts Transmit Enable.

So amend uart_configure_port() and uart_resume_port() to invoke
uart_rs485_config().  That allows removing calls to uart_rs485_config()
from drivers' ->probe() hooks and declaring the function static.

Skip any invocation of ->set_mctrl() if RS485 is enabled.  RS485 has no
hardware flow control, so the modem control lines are irrelevant and
need not be touched.  When leaving RS485 mode, reset the modem control
lines to the state stored in port->mctrl.  That way, UARTs which are
muxed between RS485 and RS232 transceivers drive the lines correctly
when switched to RS232.  (serial8250_do_startup() historically raises
the OUT1 modem signal because otherwise interrupts are not signaled on
ancient PC UARTs, but I believe that no longer applies to modern,
RS485-capable UARTs and is thus safe to be skipped.)

imx.c modifies port->mctrl whenever Transmit Enable is asserted and
deasserted.  Stop it from doing that so port->mctrl reflects the RS232
line state.

8250_omap.c deasserts Transmit Enable on ->runtime_resume() by calling
->set_mctrl().  Because that is now a no-op in RS485 mode, amend the
function to call serial8250_em485_stop_tx().

fsl_lpuart.c retrieves and applies the RS485 device tree properties
after registering the UART port.  Because applying now happens on
registration in uart_configure_port(), move retrieval of the properties
ahead of uart_add_one_port().

Link: https://lore.kernel.org/all/20220329085050.311408-1-matthias.schiffer@ew.tq-group.com/
Link: https://lore.kernel.org/all/8f538a8903795f22f9acc94a9a31b03c9c4ccacb.camel@ginzinger.com/
Fixes: d3b3404df318 ("serial: Fix incorrect rs485 polarity on uart open")
Cc: stable@vger.kernel.org # v4.14+
Reported-by: Matthias Schiffer <matthias.schiffer@ew.tq-group.com>
Reported-by: Roosen Henri <Henri.Roosen@ginzinger.com>
Tested-by: Matthias Schiffer <matthias.schiffer@ew.tq-group.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Link: https://lore.kernel.org/r/2de36eba3fbe11278d5002e4e501afe0ceaca039.1663863805.git.lukas@wunner.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c
index 871f8a05051305d7bf2fcfd9241a2597117a2921..41b8c6b27136a9cdb624e5c7c7c8bbedaeb26b53 100644 (file)
--- a/drivers/tty/serial/8250/8250_omap.c
+++ b/drivers/tty/serial/8250/8250_omap.c
@@ -342,6 +342,9 @@ static void omap8250_restore_regs(struct uart_8250_port *up)
        omap8250_update_mdr1(up, priv);
 
        up->port.ops->set_mctrl(&up->port, up->port.mctrl);
+
+       if (up->port.rs485.flags & SER_RS485_ENABLED)
+               serial8250_em485_stop_tx(up);
 }
 
 /*

diff --git a/drivers/tty/serial/8250/8250_pci.c b/drivers/tty/serial/8250/8250_pci.c
index 0052cf899e29b70800279f91528ca77f5c8d27da..8e9f247590bd4da1a0d7044f048d461e099f7958 100644 (file)
--- a/drivers/tty/serial/8250/8250_pci.c
+++ b/drivers/tty/serial/8250/8250_pci.c
@@ -1632,7 +1632,6 @@ static int pci_fintek_init(struct pci_dev *dev)
        resource_size_t bar_data[3];
        u8 config_base;
        struct serial_private *priv = pci_get_drvdata(dev);
-       struct uart_8250_port *port;
 
        if (!(pci_resource_flags(dev, 5) & IORESOURCE_IO) ||
                        !(pci_resource_flags(dev, 4) & IORESOURCE_IO) ||
@@ -1679,13 +1678,7 @@ static int pci_fintek_init(struct pci_dev *dev)
 
                pci_write_config_byte(dev, config_base + 0x06, dev->irq);
 
-               if (priv) {
-                       /* re-apply RS232/485 mode when
-                        * pciserial_resume_ports()
-                        */
-                       port = serial8250_get_port(priv->line[i]);
-                       uart_rs485_config(&port->port);
-               } else {
+               if (!priv) {
                        /* First init without port data
                         * force init to RS232 Mode
                         */

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 6a3c2ead0f1702e8e9485631c8935792d10eb38b..dfdd2db95cb364bcb859b8594cbe1c91efa9d863 100644 (file)
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -600,7 +600,7 @@ EXPORT_SYMBOL_GPL(serial8250_rpm_put);
 static int serial8250_em485_init(struct uart_8250_port *p)
 {
        if (p->em485)
-               return 0;
+               goto deassert_rts;
 
        p->em485 = kmalloc(sizeof(struct uart_8250_em485), GFP_ATOMIC);
        if (!p->em485)
@@ -616,7 +616,9 @@ static int serial8250_em485_init(struct uart_8250_port *p)
        p->em485->active_timer = NULL;
        p->em485->tx_stopped = true;
 
-       p->rs485_stop_tx(p);
+deassert_rts:
+       if (p->em485->tx_stopped)
+               p->rs485_stop_tx(p);
 
        return 0;
 }
@@ -2048,6 +2050,9 @@ EXPORT_SYMBOL_GPL(serial8250_do_set_mctrl);
 
 static void serial8250_set_mctrl(struct uart_port *port, unsigned int mctrl)
 {
+       if (port->rs485.flags & SER_RS485_ENABLED)
+               return;
+
        if (port->set_mctrl)
                port->set_mctrl(port, mctrl);
        else
@@ -3192,9 +3197,6 @@ static void serial8250_config_port(struct uart_port *port, int flags)
        if (flags & UART_CONFIG_TYPE)
                autoconfig(up);
 
-       if (port->rs485.flags & SER_RS485_ENABLED)
-               uart_rs485_config(port);
-
        /* if access method is AU, it is a 16550 with a quirk */
        if (port->type == PORT_16550A && port->iotype == UPIO_AU)
                up->bugs |= UART_BUG_NOMSR;

diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c
index fadb490861029b64f1eb3631ab9ac62f27147783..67fa113f77d475a621bc53bec3b33752abc0ad2a 100644 (file)
--- a/drivers/tty/serial/fsl_lpuart.c
+++ b/drivers/tty/serial/fsl_lpuart.c
@@ -2726,15 +2726,13 @@ static int lpuart_probe(struct platform_device *pdev)
        if (ret)
                goto failed_reset;
 
-       ret = uart_add_one_port(&lpuart_reg, &sport->port);
-       if (ret)
-               goto failed_attach_port;
-
        ret = uart_get_rs485_mode(&sport->port);
        if (ret)
                goto failed_get_rs485;
 
-       uart_rs485_config(&sport->port);
+       ret = uart_add_one_port(&lpuart_reg, &sport->port);
+       if (ret)
+               goto failed_attach_port;
 
        ret = devm_request_irq(&pdev->dev, sport->port.irq, handler, 0,
                                DRIVER_NAME, sport);
@@ -2744,9 +2742,9 @@ static int lpuart_probe(struct platform_device *pdev)
        return 0;
 
 failed_irq_request:
-failed_get_rs485:
        uart_remove_one_port(&lpuart_reg, &sport->port);
 failed_attach_port:
+failed_get_rs485:
 failed_reset:
        lpuart_disable_clks(sport);
        return ret;

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 5875ee66492b1d65136d13c924e81550d29d0652..05b432dc7a85c79065efd53d1a2d6fe6bed27b6c 100644 (file)
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -380,8 +380,7 @@ static void imx_uart_rts_active(struct imx_port *sport, u32 *ucr2)
 {
        *ucr2 &= ~(UCR2_CTSC | UCR2_CTS);
 
-       sport->port.mctrl |= TIOCM_RTS;
-       mctrl_gpio_set(sport->gpios, sport->port.mctrl);
+       mctrl_gpio_set(sport->gpios, sport->port.mctrl | TIOCM_RTS);
 }
 
 /* called with port.lock taken and irqs caller dependent */
@@ -390,8 +389,7 @@ static void imx_uart_rts_inactive(struct imx_port *sport, u32 *ucr2)
        *ucr2 &= ~UCR2_CTSC;
        *ucr2 |= UCR2_CTS;
 
-       sport->port.mctrl &= ~TIOCM_RTS;
-       mctrl_gpio_set(sport->gpios, sport->port.mctrl);
+       mctrl_gpio_set(sport->gpios, sport->port.mctrl & ~TIOCM_RTS);
 }
 
 static void start_hrtimer_ms(struct hrtimer *hrt, unsigned long msec)
@@ -2347,8 +2345,6 @@ static int imx_uart_probe(struct platform_device *pdev)
                dev_err(&pdev->dev,
                        "low-active RTS not possible when receiver is off, enabling receiver\n");
 
-       uart_rs485_config(&sport->port);
-
        /* Disable interrupts before requesting them */
        ucr1 = imx_uart_readl(sport, UCR1);
        ucr1 &= ~(UCR1_ADEN | UCR1_TRDYEN | UCR1_IDEN | UCR1_RRDYEN | UCR1_RTSDEN);

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index c7113182275a0199d04625c1d45cd2ca90f98c2c..179ee199df343ef28d00e0327c1909cbddf5fbc3 100644 (file)
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -158,15 +158,10 @@ uart_update_mctrl(struct uart_port *port, unsigned int set, unsigned int clear)
        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;
-       if (old != port->mctrl)
+       if (old != port->mctrl && !(port->rs485.flags & SER_RS485_ENABLED))
                port->ops->set_mctrl(port, port->mctrl);
        spin_unlock_irqrestore(&port->lock, flags);
 }
@@ -1391,7 +1386,7 @@ static void uart_set_rs485_termination(struct uart_port *port,
                                 !!(rs485->flags & SER_RS485_TERMINATE_BUS));
 }
 
-int uart_rs485_config(struct uart_port *port)
+static int uart_rs485_config(struct uart_port *port)
 {
        struct serial_rs485 *rs485 = &port->rs485;
        int ret;
@@ -1405,7 +1400,6 @@ int uart_rs485_config(struct uart_port *port)
 
        return ret;
 }
-EXPORT_SYMBOL_GPL(uart_rs485_config);
 
 static int uart_get_rs485_config(struct uart_port *port,
                         struct serial_rs485 __user *rs485)
@@ -1444,8 +1438,13 @@ static int uart_set_rs485_config(struct tty_struct *tty, struct uart_port *port,
 
        spin_lock_irqsave(&port->lock, flags);
        ret = port->rs485_config(port, &tty->termios, &rs485);
-       if (!ret)
+       if (!ret) {
                port->rs485 = rs485;
+
+               /* Reset RTS and other mctrl lines when disabling RS485 */
+               if (!(rs485.flags & SER_RS485_ENABLED))
+                       port->ops->set_mctrl(port, port->mctrl);
+       }
        spin_unlock_irqrestore(&port->lock, flags);
        if (ret)
                return ret;
@@ -2352,7 +2351,8 @@ int uart_suspend_port(struct uart_driver *drv, struct uart_port *uport)
 
                spin_lock_irq(&uport->lock);
                ops->stop_tx(uport);
-               ops->set_mctrl(uport, 0);
+               if (!(uport->rs485.flags & SER_RS485_ENABLED))
+                       ops->set_mctrl(uport, 0);
                /* save mctrl so it can be restored on resume */
                mctrl = uport->mctrl;
                uport->mctrl = 0;
@@ -2440,7 +2440,8 @@ int uart_resume_port(struct uart_driver *drv, struct uart_port *uport)
 
                uart_change_pm(state, UART_PM_STATE_ON);
                spin_lock_irq(&uport->lock);
-               ops->set_mctrl(uport, 0);
+               if (!(uport->rs485.flags & SER_RS485_ENABLED))
+                       ops->set_mctrl(uport, 0);
                spin_unlock_irq(&uport->lock);
                if (console_suspend_enabled || !uart_console(uport)) {
                        /* Protected by port mutex for now */
@@ -2451,7 +2452,10 @@ int uart_resume_port(struct uart_driver *drv, struct uart_port *uport)
                                if (tty)
                                        uart_change_speed(tty, state, NULL);
                                spin_lock_irq(&uport->lock);
-                               ops->set_mctrl(uport, uport->mctrl);
+                               if (!(uport->rs485.flags & SER_RS485_ENABLED))
+                                       ops->set_mctrl(uport, uport->mctrl);
+                               else
+                                       uart_rs485_config(uport);
                                ops->start_tx(uport);
                                spin_unlock_irq(&uport->lock);
                                tty_port_set_initialized(port, 1);
@@ -2558,10 +2562,10 @@ uart_configure_port(struct uart_driver *drv, struct uart_state *state,
                 */
                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);
+               if (!(port->rs485.flags & SER_RS485_ENABLED))
+                       port->ops->set_mctrl(port, port->mctrl);
+               else
+                       uart_rs485_config(port);
                spin_unlock_irqrestore(&port->lock, flags);
 
                /*

diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index b4c21f84ad79c36d196227f25463778994498e28..d657f2a42a7b8fadd84d88952e5e2a022b36b32c 100644 (file)
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -951,5 +951,4 @@ static inline int uart_handle_break(struct uart_port *port)
                                         !((cflag) & CLOCAL))
 
 int uart_get_rs485_mode(struct uart_port *port);
-int uart_rs485_config(struct uart_port *port);
 #endif /* LINUX_SERIAL_CORE_H */