[PATCH v2] serial: xilinx_uartps: fix runtime PM race during probe

[Radhey Shyam Pandey]

From: Shubhrajyoti Datta <shubhrajyoti.datta@xxxxxxx>

pm_runtime_enable() was called with usage_count=0, allowing the PM
core to immediately queue a deferred suspend via pm_runtime_work.
This raced with console write, causing cdns_runtime_suspend to
fire before the port was fully registered.

Hold a reference with pm_runtime_get_noresume() before enabling
runtime PM.

Fixes: d62100f1aac2 ("serial: xilinx_uartps: Add pm runtime support")
Signed-off-by: Shubhrajyoti Datta <shubhrajyoti.datta@xxxxxxx>
Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@xxxxxxx>
---
Changes for v2:
- Add my signed-off tag.
Link to v1: https://lore.kernel.org/all/20261109070915.727524-1-radhey.shyam.pandey@xxxxxxx
- Use latest base.
---
 drivers/tty/serial/xilinx_uartps.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/tty/serial/xilinx_uartps.c b/drivers/tty/serial/xilinx_uartps.c
index e8c4b1fa7658..aa3e820760b1 100644
--- a/drivers/tty/serial/xilinx_uartps.c
+++ b/drivers/tty/serial/xilinx_uartps.c
@@ -1799,6 +1799,7 @@ static int cdns_uart_probe(struct platform_device *pdev)
 	pm_runtime_use_autosuspend(&pdev->dev);
 	pm_runtime_set_autosuspend_delay(&pdev->dev, UART_AUTOSUSPEND_TIMEOUT);
 	pm_runtime_set_active(&pdev->dev);
+	pm_runtime_get_noresume(&pdev->dev);
 	pm_runtime_enable(&pdev->dev);
 	device_init_wakeup(port->dev, true);
 
@@ -1823,6 +1824,8 @@ static int cdns_uart_probe(struct platform_device *pdev)
 			"uart_add_one_port() failed; err=%i\n", rc);
 		goto err_out_pm_disable;
 	}
+	pm_runtime_mark_last_busy(&pdev->dev);
+	pm_runtime_put_autosuspend(&pdev->dev);
 
 #ifdef CONFIG_SERIAL_XILINX_PS_UART_CONSOLE
 	/* This is not port which is used for console that's why clean it up */
@@ -1841,6 +1844,7 @@ static int cdns_uart_probe(struct platform_device *pdev)
 	return 0;
 
 err_out_pm_disable:
+	pm_runtime_put_noidle(&pdev->dev);
 	pm_runtime_disable(&pdev->dev);
 	pm_runtime_set_suspended(&pdev->dev);
 	pm_runtime_dont_use_autosuspend(&pdev->dev);

base-commit: 7475ea8b58616b33c04afb976cf0fbaad9dd63fb
-- 
2.44.4