serial: 8250: Provide flag for IER toggling for RS485

For RS485 mode, if SER_RS485_RX_DURING_TX is not available, the
console ->write() callback needs to enable/disable Tx. It does
this by calling the ->rs485_start_tx() and ->rs485_stop_tx()
callbacks. However, some of these callbacks also disable/enable
interrupts and makes power management calls. This causes 2
problems for console writing:

1. A console write can occur in contexts that are illegal for
   pm_runtime_*(). It is not even necessary for console writing
   to use pm_runtime_*() because a console already does this in
   serial8250_console_setup() and serial8250_console_exit().

2. The console ->write() callback already handles
   disabling/enabling the interrupts by properly restoring the
   previous IER value.

Add an argument @toggle_ier to the ->rs485_start_tx() and
->rs485_stop_tx() callbacks to specify if they may disable/enable
receive interrupts while using pm_runtime_*(). Console writing
will not allow the toggling.

For all call sites other than console writing there is no
functional change.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20250107212702.169493-5-john.ogness@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
index e5310c65cf52b3f6a493d8648f46fdbe44d1475a..11e05aa014e54902313ba26e9b1bd5772345ec7a 100644 (file)
--- a/drivers/tty/serial/8250/8250.h
+++ b/drivers/tty/serial/8250/8250.h
@@ -231,8 +231,8 @@ void serial8250_rpm_put_tx(struct uart_8250_port *p);
 
 int serial8250_em485_config(struct uart_port *port, struct ktermios *termios,
                            struct serial_rs485 *rs485);
-void serial8250_em485_start_tx(struct uart_8250_port *p);
-void serial8250_em485_stop_tx(struct uart_8250_port *p);
+void serial8250_em485_start_tx(struct uart_8250_port *p, bool toggle_ier);
+void serial8250_em485_stop_tx(struct uart_8250_port *p, bool toggle_ier);
 void serial8250_em485_destroy(struct uart_8250_port *p);
 extern struct serial_rs485 serial8250_em485_supported;
 

diff --git a/drivers/tty/serial/8250/8250_bcm2835aux.c b/drivers/tty/serial/8250/8250_bcm2835aux.c
index fdb53b54e99e60a00aab02d0785bb0e31beeee6b..0609582a62f746506120cb951190fc6e3d98ee25 100644 (file)
--- a/drivers/tty/serial/8250/8250_bcm2835aux.c
+++ b/drivers/tty/serial/8250/8250_bcm2835aux.c
@@ -46,7 +46,7 @@ struct bcm2835aux_data {
        u32 cntl;
 };
 
-static void bcm2835aux_rs485_start_tx(struct uart_8250_port *up)
+static void bcm2835aux_rs485_start_tx(struct uart_8250_port *up, bool toggle_ier)
 {
        if (!(up->port.rs485.flags & SER_RS485_RX_DURING_TX)) {
                struct bcm2835aux_data *data = dev_get_drvdata(up->port.dev);
@@ -65,7 +65,7 @@ static void bcm2835aux_rs485_start_tx(struct uart_8250_port *up)
                serial8250_out_MCR(up, UART_MCR_RTS);
 }
 
-static void bcm2835aux_rs485_stop_tx(struct uart_8250_port *up)
+static void bcm2835aux_rs485_stop_tx(struct uart_8250_port *up, bool toggle_ier)
 {
        if (up->port.rs485.flags & SER_RS485_RTS_AFTER_SEND)
                serial8250_out_MCR(up, 0);

diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c
index 42b4aa56b9020edd8cb3d96ff1ab5c990675dde8..c2b75e3f106d0cbdd2fd99eb5f1a534b6863cc7f 100644 (file)
--- a/drivers/tty/serial/8250/8250_omap.c
+++ b/drivers/tty/serial/8250/8250_omap.c
@@ -365,7 +365,7 @@ static void omap8250_restore_regs(struct uart_8250_port *up)
 
        if (up->port.rs485.flags & SER_RS485_ENABLED &&
            up->port.rs485_config == serial8250_em485_config)
-               serial8250_em485_stop_tx(up);
+               serial8250_em485_stop_tx(up, true);
 }
 
 /*

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 15abd95fcf066dbba888230eefe3e710025f05ef..d7976a21cca9ce50557ca5f13bb01448ced0728b 100644 (file)
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -578,7 +578,7 @@ static int serial8250_em485_init(struct uart_8250_port *p)
 
 deassert_rts:
        if (p->em485->tx_stopped)
-               p->rs485_stop_tx(p);
+               p->rs485_stop_tx(p, true);
 
        return 0;
 }
@@ -1398,10 +1398,11 @@ static void serial8250_stop_rx(struct uart_port *port)
 /**
  * serial8250_em485_stop_tx() - generic ->rs485_stop_tx() callback
  * @p: uart 8250 port
+ * @toggle_ier: true to allow enabling receive interrupts
  *
  * Generic callback usable by 8250 uart drivers to stop rs485 transmission.
  */
-void serial8250_em485_stop_tx(struct uart_8250_port *p)
+void serial8250_em485_stop_tx(struct uart_8250_port *p, bool toggle_ier)
 {
        unsigned char mcr = serial8250_in_MCR(p);
 
@@ -1422,8 +1423,10 @@ void serial8250_em485_stop_tx(struct uart_8250_port *p)
        if (!(p->port.rs485.flags & SER_RS485_RX_DURING_TX)) {
                serial8250_clear_and_reinit_fifos(p);
 
-               p->ier |= UART_IER_RLSI | UART_IER_RDI;
-               serial_port_out(&p->port, UART_IER, p->ier);
+               if (toggle_ier) {
+                       p->ier |= UART_IER_RLSI | UART_IER_RDI;
+                       serial_port_out(&p->port, UART_IER, p->ier);
+               }
        }
 }
 EXPORT_SYMBOL_GPL(serial8250_em485_stop_tx);
@@ -1438,7 +1441,7 @@ static enum hrtimer_restart serial8250_em485_handle_stop_tx(struct hrtimer *t)
        serial8250_rpm_get(p);
        uart_port_lock_irqsave(&p->port, &flags);
        if (em485->active_timer == &em485->stop_tx_timer) {
-               p->rs485_stop_tx(p);
+               p->rs485_stop_tx(p, true);
                em485->active_timer = NULL;
                em485->tx_stopped = true;
        }
@@ -1470,7 +1473,7 @@ static void __stop_tx_rs485(struct uart_8250_port *p, u64 stop_delay)
                em485->active_timer = &em485->stop_tx_timer;
                hrtimer_start(&em485->stop_tx_timer, ns_to_ktime(stop_delay), HRTIMER_MODE_REL);
        } else {
-               p->rs485_stop_tx(p);
+               p->rs485_stop_tx(p, true);
                em485->active_timer = NULL;
                em485->tx_stopped = true;
        }
@@ -1559,6 +1562,7 @@ static inline void __start_tx(struct uart_port *port)
 /**
  * serial8250_em485_start_tx() - generic ->rs485_start_tx() callback
  * @up: uart 8250 port
+ * @toggle_ier: true to allow disabling receive interrupts
  *
  * Generic callback usable by 8250 uart drivers to start rs485 transmission.
  * Assumes that setting the RTS bit in the MCR register means RTS is high.
@@ -1566,11 +1570,11 @@ static inline void __start_tx(struct uart_port *port)
  * stoppable by disabling the UART_IER_RDI interrupt.  (Some chips set the
  * UART_LSR_DR bit even when UART_IER_RDI is disabled, foiling this approach.)
  */
-void serial8250_em485_start_tx(struct uart_8250_port *up)
+void serial8250_em485_start_tx(struct uart_8250_port *up, bool toggle_ier)
 {
        unsigned char mcr = serial8250_in_MCR(up);
 
-       if (!(up->port.rs485.flags & SER_RS485_RX_DURING_TX))
+       if (!(up->port.rs485.flags & SER_RS485_RX_DURING_TX) && toggle_ier)
                serial8250_stop_rx(&up->port);
 
        if (up->port.rs485.flags & SER_RS485_RTS_ON_SEND)
@@ -1604,7 +1608,7 @@ static bool start_tx_rs485(struct uart_port *port)
        if (em485->tx_stopped) {
                em485->tx_stopped = false;
 
-               up->rs485_start_tx(up);
+               up->rs485_start_tx(up, true);
 
                if (up->port.rs485.delay_rts_before_send > 0) {
                        em485->active_timer = &em485->start_tx_timer;
@@ -3424,7 +3428,7 @@ void serial8250_console_write(struct uart_8250_port *up, const char *s,
 
        if (em485) {
                if (em485->tx_stopped)
-                       up->rs485_start_tx(up);
+                       up->rs485_start_tx(up, false);
                mdelay(port->rs485.delay_rts_before_send);
        }
 
@@ -3462,7 +3466,7 @@ void serial8250_console_write(struct uart_8250_port *up, const char *s,
        if (em485) {
                mdelay(port->rs485.delay_rts_after_send);
                if (em485->tx_stopped)
-                       up->rs485_stop_tx(up);
+                       up->rs485_stop_tx(up, false);
        }
 
        serial_port_out(port, UART_IER, ier);

diff --git a/include/linux/serial_8250.h b/include/linux/serial_8250.h
index e0717c8393d7fe56fb3997a704b7a8de875f7343..144de7a7948de30e97df7a1577aecb56fe4ccac6 100644 (file)
--- a/include/linux/serial_8250.h
+++ b/include/linux/serial_8250.h
@@ -161,8 +161,8 @@ struct uart_8250_port {
        void                    (*dl_write)(struct uart_8250_port *up, u32 value);
 
        struct uart_8250_em485 *em485;
-       void                    (*rs485_start_tx)(struct uart_8250_port *);
-       void                    (*rs485_stop_tx)(struct uart_8250_port *);
+       void                    (*rs485_start_tx)(struct uart_8250_port *up, bool toggle_ier);
+       void                    (*rs485_stop_tx)(struct uart_8250_port *up, bool toggle_ier);
 
        /* Serial port overrun backoff */
        struct delayed_work overrun_backoff;