serial: mctrl_gpio: split disable_ms into sync and no_sync APIs

The following splat has been observed on a SAMA5D27 platform using
atmel_serial:

BUG: sleeping function called from invalid context at kernel/irq/manage.c:738
in_atomic(): 1, irqs_disabled(): 128, non_block: 0, pid: 27, name: kworker/u5:0
preempt_count: 1, expected: 0
INFO: lockdep is turned off.
irq event stamp: 0
hardirqs last enabled at (0): [<00000000>] 0x0
hardirqs last disabled at (0): [<c01588f0>] copy_process+0x1c4c/0x7bec
softirqs last enabled at (0): [<c0158944>] copy_process+0x1ca0/0x7bec
softirqs last disabled at (0): [<00000000>] 0x0
CPU: 0 UID: 0 PID: 27 Comm: kworker/u5:0 Not tainted 6.13.0-rc7+ #74
Hardware name: Atmel SAMA5
Workqueue: hci0 hci_power_on [bluetooth]
Call trace:
unwind_backtrace from show_stack+0x18/0x1c
show_stack from dump_stack_lvl+0x44/0x70
dump_stack_lvl from __might_resched+0x38c/0x598
__might_resched from disable_irq+0x1c/0x48
disable_irq from mctrl_gpio_disable_ms+0x74/0xc0
mctrl_gpio_disable_ms from atmel_disable_ms.part.0+0x80/0x1f4
atmel_disable_ms.part.0 from atmel_set_termios+0x764/0x11e8
atmel_set_termios from uart_change_line_settings+0x15c/0x994
uart_change_line_settings from uart_set_termios+0x2b0/0x668
uart_set_termios from tty_set_termios+0x600/0x8ec
tty_set_termios from ttyport_set_flow_control+0x188/0x1e0
ttyport_set_flow_control from wilc_setup+0xd0/0x524 [hci_wilc]
wilc_setup [hci_wilc] from hci_dev_open_sync+0x330/0x203c [bluetooth]
hci_dev_open_sync [bluetooth] from hci_dev_do_open+0x40/0xb0 [bluetooth]
hci_dev_do_open [bluetooth] from hci_power_on+0x12c/0x664 [bluetooth]
hci_power_on [bluetooth] from process_one_work+0x998/0x1a38
process_one_work from worker_thread+0x6e0/0xfb4
worker_thread from kthread+0x3d4/0x484
kthread from ret_from_fork+0x14/0x28

This warning is emitted when trying to toggle, at the highest level,
some flow control (with serdev_device_set_flow_control) in a device
driver. At the lowest level, the atmel_serial driver is using
serial_mctrl_gpio lib to enable/disable the corresponding IRQs
accordingly. The warning emitted by CONFIG_DEBUG_ATOMIC_SLEEP is due to
disable_irq (called in mctrl_gpio_disable_ms) being possibly called in
some atomic context (some tty drivers perform modem lines configuration
in regions protected by port lock).

Split mctrl_gpio_disable_ms into two differents APIs, a non-blocking one
and a blocking one. Replace mctrl_gpio_disable_ms calls with the
relevant version depending on whether the call is protected by some port
lock.

Suggested-by: Jiri Slaby <[e-mail]>
Signed-off-by: Alexis Lothoré <[e-mail]>
Acked-by: Richard Genoud <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

Documentation/driver-api/serial/driver.rst

···
 .. kernel-doc:: drivers/tty/serial/serial_mctrl_gpio.c
    :identifiers: mctrl_gpio_init mctrl_gpio_to_gpiod
            mctrl_gpio_set mctrl_gpio_get mctrl_gpio_enable_ms
-           mctrl_gpio_disable_ms
+           mctrl_gpio_disable_ms_sync mctrl_gpio_disable_ms_no_sync

drivers/tty/serial/8250/8250_port.c

···
 	if (up->bugs & UART_BUG_NOMSR)
 		return;
 
-	mctrl_gpio_disable_ms(up->gpios);
+	mctrl_gpio_disable_ms_no_sync(up->gpios);
 
 	up->ier &= ~UART_IER_MSI;
 	serial_port_out(port, UART_IER, up->ier);

drivers/tty/serial/atmel_serial.c

···
 
 	atmel_port->ms_irq_enabled = false;
 
-	mctrl_gpio_disable_ms(atmel_port->gpios);
+	mctrl_gpio_disable_ms_no_sync(atmel_port->gpios);
 
 	if (!mctrl_gpio_to_gpiod(atmel_port->gpios, UART_GPIO_CTS))
 		idr |= ATMEL_US_CTSIC;

drivers/tty/serial/imx.c

···
 		imx_uart_dma_exit(sport);
 	}
 
-	mctrl_gpio_disable_ms(sport->gpios);
+	mctrl_gpio_disable_ms_sync(sport->gpios);
 
 	uart_port_lock_irqsave(&sport->port, &flags);
 	ucr2 = imx_uart_readl(sport, UCR2);

drivers/tty/serial/serial_mctrl_gpio.c

···
 }
 EXPORT_SYMBOL_GPL(mctrl_gpio_enable_ms);
 
-/**
- * mctrl_gpio_disable_ms - disable irqs and handling of changes to the ms lines
- * @gpios: gpios to disable
- */
-void mctrl_gpio_disable_ms(struct mctrl_gpios *gpios)
+static void mctrl_gpio_disable_ms(struct mctrl_gpios *gpios, bool sync)
 {
 	enum mctrl_gpio_idx i;
 
···
 		if (!gpios->irq[i])
 			continue;
 
-		disable_irq(gpios->irq[i]);
+		if (sync)
+			disable_irq(gpios->irq[i]);
+		else
+			disable_irq_nosync(gpios->irq[i]);
 	}
 }
-EXPORT_SYMBOL_GPL(mctrl_gpio_disable_ms);
+
+/**
+ * mctrl_gpio_disable_ms_sync - disable irqs and handling of changes to the ms
+ * lines, and wait for any pending IRQ to be processed
+ * @gpios: gpios to disable
+ */
+void mctrl_gpio_disable_ms_sync(struct mctrl_gpios *gpios)
+{
+	mctrl_gpio_disable_ms(gpios, true);
+}
+EXPORT_SYMBOL_GPL(mctrl_gpio_disable_ms_sync);
+
+/**
+ * mctrl_gpio_disable_ms_no_sync - disable irqs and handling of changes to the
+ * ms lines, and return immediately
+ * @gpios: gpios to disable
+ */
+void mctrl_gpio_disable_ms_no_sync(struct mctrl_gpios *gpios)
+{
+	mctrl_gpio_disable_ms(gpios, false);
+}
+EXPORT_SYMBOL_GPL(mctrl_gpio_disable_ms_no_sync);
 
 void mctrl_gpio_enable_irq_wake(struct mctrl_gpios *gpios)
 {

drivers/tty/serial/serial_mctrl_gpio.h

···
 void mctrl_gpio_enable_ms(struct mctrl_gpios *gpios);
 
 /*
- * Disable gpio interrupts to report status line changes.
+ * Disable gpio interrupts to report status line changes, and block until
+ * any corresponding IRQ is processed
  */
-void mctrl_gpio_disable_ms(struct mctrl_gpios *gpios);
+void mctrl_gpio_disable_ms_sync(struct mctrl_gpios *gpios);
+
+/*
+ * Disable gpio interrupts to report status line changes, and return
+ * immediately
+ */
+void mctrl_gpio_disable_ms_no_sync(struct mctrl_gpios *gpios);
 
 /*
  * Enable gpio wakeup interrupts to enable wake up source.
···
 {
 }
 
-static inline void mctrl_gpio_disable_ms(struct mctrl_gpios *gpios)
+static inline void mctrl_gpio_disable_ms_sync(struct mctrl_gpios *gpios)
+{
+}
+
+static inline void mctrl_gpio_disable_ms_no_sync(struct mctrl_gpios *gpios)
 {
 }
 

drivers/tty/serial/sh-sci.c

···
 	dev_dbg(port->dev, "%s(%d)\n", __func__, port->line);
 
 	s->autorts = false;
-	mctrl_gpio_disable_ms(to_sci_port(port)->gpios);
+	mctrl_gpio_disable_ms_sync(to_sci_port(port)->gpios);
 
 	uart_port_lock_irqsave(port, &flags);
 	sci_stop_rx(port);

drivers/tty/serial/stm32-usart.c

···
 
 static void stm32_usart_disable_ms(struct uart_port *port)
 {
-	mctrl_gpio_disable_ms(to_stm32_port(port)->gpios);
+	mctrl_gpio_disable_ms_sync(to_stm32_port(port)->gpios);
 }
 
 /* Transmit stop */