[PATCH] serial: qcom-geni: fix enabling deactivated interrupt

[Krzysztof Kozlowski]

The driver have a race, experienced only with PREEMPT_RT patchset:

CPU0                         | CPU1
==================================================================
qcom_geni_serial_probe       |
  uart_add_one_port          |
                             | serdev_drv_probe
                             |   qca_serdev_probe
                             |     serdev_device_open
                             |       uart_open
                             |         uart_startup
                             |           qcom_geni_serial_startup
                             |             enable_irq
                             |               __irq_startup
                             |                 WARN_ON()
                             |                 IRQ not activated
  request_threaded_irq       |
    irq_domain_activate_irq  |

The warning:

  894000.serial: ttyHS1 at MMIO 0x894000 (irq = 144, base_baud = 0) is a MSM
  serial serial0: tty port ttyHS1 registered
  WARNING: CPU: 7 PID: 107 at kernel/irq/chip.c:241 __irq_startup+0x78/0xd8
  ...
  qcom_geni_serial 894000.serial: serial engine reports 0 RX bytes in!

Adding UART port triggers probe of child serial devices - serdev and
eventually Qualcomm Bluetooth hci_qca driver.  This opens UART port
which enables the interrupt before it got activated in
request_threaded_irq().  The issue originates in commit f3974413cf02
("tty: serial: qcom_geni_serial: Wakeup IRQ cleanup") and discussion on
mailing list [1].  However the above commit does not explain why the
uart_add_one_port() is moved above requesting interrupt.

[1] https://lore.kernel.org/all/5d9f3dfa.1c69fb81.84c4b.30bf@xxxxxxxxxxxxx/

Fixes: f3974413cf02 ("tty: serial: qcom_geni_serial: Wakeup IRQ cleanup")
Cc: <stable@xxxxxxxxxxxxxxx>
Cc: Stephen Boyd <swboyd@xxxxxxxxxxxx>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>
---
 drivers/tty/serial/qcom_geni_serial.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c
index 08dc3e2a729c..8582479f0211 100644
--- a/drivers/tty/serial/qcom_geni_serial.c
+++ b/drivers/tty/serial/qcom_geni_serial.c
@@ -1664,19 +1664,18 @@ static int qcom_geni_serial_probe(struct platform_device *pdev)
 	uport->private_data = &port->private_data;
 	platform_set_drvdata(pdev, port);
 
-	ret = uart_add_one_port(drv, uport);
-	if (ret)
-		return ret;
-
 	irq_set_status_flags(uport->irq, IRQ_NOAUTOEN);
 	ret = devm_request_irq(uport->dev, uport->irq, qcom_geni_serial_isr,
 			IRQF_TRIGGER_HIGH, port->name, uport);
 	if (ret) {
 		dev_err(uport->dev, "Failed to get IRQ ret %d\n", ret);
-		uart_remove_one_port(drv, uport);
 		return ret;
 	}
 
+	ret = uart_add_one_port(drv, uport);
+	if (ret)
+		return ret;
+
 	/*
 	 * Set pm_runtime status as ACTIVE so that wakeup_irq gets
 	 * enabled/disabled from dev_pm_arm_wake_irq during system
-- 
2.34.1