[PATCH 1/6] tty: serial: change uart_ops.pm callback to return int

[Praveen Talari <praveen.talari@oss.qualcomm.com>]

The uart_ops.pm callback is currently declared void, causing
uart_change_pm() to silently discard any error from a driver's power
management implementation. Worse, state->pm_state is unconditionally
updated even when the hardware transition failed, causing the serial core
to track a power state that does not reflect reality. Subsequent calls to
uart_change_pm() will then see the (stale) state as matching and skip the
callback entirely, leaving the hardware stuck in the wrong state with no
further recovery attempt.

Change the uart_ops.pm callback signature from void to int. Update
uart_change_pm() to propagate the driver's return value and only commit
state->pm_state on success, preserving consistency between software state
and hardware state across all transitions.

Update all call sites in serial_core.c:

  uart_port_startup(): propagate the error so that port open fails
  cleanly if the hardware cannot be powered on, rather than proceeding
  to call ops->startup() on an unpowered port.

  uart_suspend_port(): return the error directly so the PM framework
  is aware of the failed transition and can react accordingly.

  uart_resume_port(): propagate on both the console-resume and the
  suspended-port-restore paths so a failed power-on is not hidden
  from the PM core.

  uart_configure_port(): log and return early if power-on fails at
  probe time; log a warning if power-down fails after configuration,
  since the port is already registered at that point.

  uart_tty_port_shutdown(), uart_hangup(): log via dev_err() since
  these are void paths where propagation is not meaningful; teardown
  continues regardless.

  uart_line_info(): skip the modem-control status read if power-on
  fails to avoid accessing an unpowered port; log a warning if the
  original power state cannot be restored afterward.

  uart_poll_init(): propagate the power-on error; log a warning if
  the saved power state cannot be restored after a failed poll init.

Also update the uart_port.pm field (used by 8250 sub-drivers that
install a per-port pm function pointer directly) and its kernel-doc to
the new int-returning signature.

No functional change for any existing driver since all current .pm
implementations will be updated to return 0.

Signed-off-by: Praveen Talari <praveen.talari@oss.qualcomm.com>
---
 drivers/tty/serial/serial_core.c | 89 ++++++++++++++++++++++++++++------------
 include/linux/serial_core.h      | 10 +++--
 2 files changed, 69 insertions(+), 30 deletions(-)

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index a530ad372b43..e624a67a9395 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -52,8 +52,8 @@ static struct lock_class_key port_lock_key;
  */
 #define RS485_MAX_RTS_DELAY	100 /* msecs */
 
-static void uart_change_pm(struct uart_state *state,
-			   enum uart_pm_state pm_state);
+static int uart_change_pm(struct uart_state *state,
+			  enum uart_pm_state pm_state);
 
 static void uart_port_shutdown(struct tty_port *port);
 
@@ -312,7 +312,9 @@ static int uart_port_startup(struct tty_struct *tty, struct uart_state *state,
 	/*
 	 * Make sure the device is in D0 state.
 	 */
-	uart_change_pm(state, UART_PM_STATE_ON);
+	retval = uart_change_pm(state, UART_PM_STATE_ON);
+	if (retval)
+		return retval;
 
 	retval = uart_alloc_xmit_buf(&state->port);
 	if (retval)
@@ -1741,7 +1743,8 @@ static void uart_tty_port_shutdown(struct tty_port *port)
 
 	uart_free_xmit_buf(port);
 
-	uart_change_pm(state, UART_PM_STATE_OFF);
+	if (uart_change_pm(state, UART_PM_STATE_OFF))
+		dev_err(uport->dev, "failed to set power state off on shutdown\n");
 }
 
 static void uart_wait_until_sent(struct tty_struct *tty, int timeout)
@@ -1831,8 +1834,13 @@ static void uart_hangup(struct tty_struct *tty)
 			port->count = 0;
 		tty_port_set_active(port, false);
 		tty_port_tty_set(port, NULL);
-		if (uport && !uart_console(uport))
-			uart_change_pm(state, UART_PM_STATE_OFF);
+		if (uport && !uart_console(uport)) {
+			int ret = uart_change_pm(state, UART_PM_STATE_OFF);
+
+			if (ret)
+				dev_err(uport->dev,
+					"failed to set power state off on hangup\n");
+		}
 		wake_up_interruptible(&port->open_wait);
 		wake_up_interruptible(&port->delta_msr_wait);
 	}
@@ -1994,12 +2002,17 @@ static void uart_line_info(struct seq_file *m, struct uart_state *state)
 
 	if (capable(CAP_SYS_ADMIN)) {
 		pm_state = state->pm_state;
-		if (pm_state != UART_PM_STATE_ON)
-			uart_change_pm(state, UART_PM_STATE_ON);
+		if (pm_state != UART_PM_STATE_ON) {
+			if (uart_change_pm(state, UART_PM_STATE_ON))
+				goto line_info_end;
+		}
 		scoped_guard(uart_port_lock_irq, uport)
 			status = uport->ops->get_mctrl(uport);
-		if (pm_state != UART_PM_STATE_ON)
-			uart_change_pm(state, pm_state);
+		if (pm_state != UART_PM_STATE_ON) {
+			if (uart_change_pm(state, pm_state))
+				dev_err(uport->dev,
+					"failed to restore power state after line info\n");
+		}
 
 		seq_printf(m, " tx:%u rx:%u",
 				uport->icount.tx, uport->icount.rx);
@@ -2036,6 +2049,7 @@ static void uart_line_info(struct seq_file *m, struct uart_state *state)
 
 		seq_puts(m, stat_buf);
 	}
+line_info_end:
 	seq_putc(m, '\n');
 #undef STATBIT
 #undef INFOBIT
@@ -2265,17 +2279,24 @@ EXPORT_SYMBOL_GPL(uart_set_options);
  * @pm_state: new state
  *
  * Locking: port->mutex has to be held
+ *
+ * Returns 0 on success, negative error code on failure.
  */
-static void uart_change_pm(struct uart_state *state,
-			   enum uart_pm_state pm_state)
+static int uart_change_pm(struct uart_state *state,
+			  enum uart_pm_state pm_state)
 {
 	struct uart_port *port = uart_port_check(state);
 
 	if (state->pm_state != pm_state) {
-		if (port && port->ops->pm)
-			port->ops->pm(port, pm_state, state->pm_state);
+		if (port && port->ops->pm) {
+			int ret = port->ops->pm(port, pm_state, state->pm_state);
+
+			if (ret)
+				return ret;
+		}
 		state->pm_state = pm_state;
 	}
+	return 0;
 }
 
 struct uart_match {
@@ -2364,9 +2385,7 @@ int uart_suspend_port(struct uart_driver *drv, struct uart_port *uport)
 	if (uart_console(uport))
 		console_suspend(uport->cons);
 
-	uart_change_pm(state, UART_PM_STATE_OFF);
-
-	return 0;
+	return uart_change_pm(state, UART_PM_STATE_OFF);
 }
 EXPORT_SYMBOL(uart_suspend_port);
 
@@ -2408,8 +2427,12 @@ int uart_resume_port(struct uart_driver *drv, struct uart_port *uport)
 		if (port->tty && termios.c_cflag == 0)
 			termios = port->tty->termios;
 
-		if (console_suspend_enabled)
-			uart_change_pm(state, UART_PM_STATE_ON);
+		if (console_suspend_enabled) {
+			int ret = uart_change_pm(state, UART_PM_STATE_ON);
+
+			if (ret)
+				return ret;
+		}
 		uport->ops->set_termios(uport, &termios, NULL);
 		if (!console_suspend_enabled && uport->ops->start_rx) {
 			guard(uart_port_lock_irq)(uport);
@@ -2423,7 +2446,9 @@ int uart_resume_port(struct uart_driver *drv, struct uart_port *uport)
 		const struct uart_ops *ops = uport->ops;
 		int ret;
 
-		uart_change_pm(state, UART_PM_STATE_ON);
+		ret = uart_change_pm(state, UART_PM_STATE_ON);
+		if (ret)
+			return ret;
 		scoped_guard(uart_port_lock_irq, uport)
 			if (!(uport->rs485.flags & SER_RS485_ENABLED))
 				ops->set_mctrl(uport, 0);
@@ -2541,7 +2566,12 @@ uart_configure_port(struct uart_driver *drv, struct uart_state *state,
 			console_lock();
 
 		/* Power up port for set_mctrl() */
-		uart_change_pm(state, UART_PM_STATE_ON);
+		if (uart_change_pm(state, UART_PM_STATE_ON)) {
+			dev_err(port->dev, "failed to power up port\n");
+			if (uart_console(port))
+				console_unlock();
+			return;
+		}
 
 		/*
 		 * Ensure that the modem control lines are de-activated.
@@ -2578,8 +2608,10 @@ uart_configure_port(struct uart_driver *drv, struct uart_state *state,
 		 * Power down all ports by default, except the
 		 * console if we have one.
 		 */
-		if (!uart_console(port))
-			uart_change_pm(state, UART_PM_STATE_OFF);
+		if (!uart_console(port)) {
+			if (uart_change_pm(state, UART_PM_STATE_OFF))
+				dev_err(port->dev, "failed to power down port\n");
+		}
 	}
 }
 
@@ -2608,7 +2640,9 @@ static int uart_poll_init(struct tty_driver *driver, int line, char *options)
 		return -1;
 
 	pm_state = state->pm_state;
-	uart_change_pm(state, UART_PM_STATE_ON);
+	ret = uart_change_pm(state, UART_PM_STATE_ON);
+	if (ret)
+		return ret;
 
 	if (port->ops->poll_init) {
 		/*
@@ -2626,8 +2660,11 @@ static int uart_poll_init(struct tty_driver *driver, int line, char *options)
 		console_list_unlock();
 	}
 
-	if (ret)
-		uart_change_pm(state, pm_state);
+	if (ret) {
+		if (uart_change_pm(state, pm_state))
+			dev_err(port->dev,
+				"failed to restore power state after poll init failure\n");
+	}
 
 	return ret;
 }
diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index bdc214386e4a..c82839028220 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -269,8 +269,8 @@ struct gpio_desc;
  *
  *	Locking: caller holds tty_port->mutex
  *
- * @pm: ``void ()(struct uart_port *port, unsigned int state,
- *		 unsigned int oldstate)``
+ * @pm: ``int ()(struct uart_port *port, unsigned int state,
+ *		unsigned int oldstate)``
  *
  *	Perform any power management related activities on the specified @port.
  *	@state indicates the new state (defined by enum uart_pm_state),
@@ -282,6 +282,8 @@ struct gpio_desc;
  *	closed, except when the @port is also the system console. This will
  *	occur even if %CONFIG_PM is not set.
  *
+ *	Returns 0 on success, negative error code on failure.
+ *
  *	Locking: none.
  *	Interrupts: caller dependent.
  *
@@ -391,7 +393,7 @@ struct uart_ops {
 	void		(*set_termios)(struct uart_port *, struct ktermios *new,
 				       const struct ktermios *old);
 	void		(*set_ldisc)(struct uart_port *, struct ktermios *);
-	void		(*pm)(struct uart_port *, unsigned int state,
+	int		(*pm)(struct uart_port *port, unsigned int state,
 			      unsigned int oldstate);
 	const char	*(*type)(struct uart_port *);
 	void		(*release_port)(struct uart_port *);
@@ -464,7 +466,7 @@ struct uart_port {
 	void			(*throttle)(struct uart_port *port);
 	void			(*unthrottle)(struct uart_port *port);
 	int			(*handle_irq)(struct uart_port *);
-	void			(*pm)(struct uart_port *, unsigned int state,
+	int			(*pm)(struct uart_port *port, unsigned int state,
 				      unsigned int old);
 	void			(*handle_break)(struct uart_port *);
 	int			(*rs485_config)(struct uart_port *,

-- 
2.34.1