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 <jirislaby@kernel.org>
Signed-off-by: Alexis Lothoré <alexis.lothore@bootlin.com>
Acked-by: Richard Genoud <richard.genoud@bootlin.com>
Link: https://lore.kernel.org/r/20250217-atomic_sleep_mctrl_serial_gpio-v3-1-59324b313eef@bootlin.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 27 insertions, 7 deletions

diff --git a/drivers/tty/serial/serial_mctrl_gpio.c b/drivers/tty/serial/serial_mctrl_gpio.c
index 85c172ad1de9..7b02c5ca4afd 100644
--- a/drivers/tty/serial/serial_mctrl_gpio.c
+++ b/drivers/tty/serial/serial_mctrl_gpio.c
@@ -296,11 +296,7 @@ void mctrl_gpio_enable_ms(struct mctrl_gpios *gpios)
 }
 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;
 
@@ -316,10 +312,34 @@ void mctrl_gpio_disable_ms(struct mctrl_gpios *gpios)
 		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)
 {