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@mx.google.com/

Fixes: f3974413cf02 ("tty: serial: qcom_geni_serial: Wakeup IRQ cleanup") Cc: stable@vger.kernel.org Cc: Stephen Boyd swboyd@chromium.org Signed-off-by: Krzysztof Kozlowski krzysztof.kozlowski@linaro.org --- 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