Re: [PATCH v12 1/1] serial: core: Start managing serial controllers to enable runtime PM

[Tony Lindgren <tony@atomide.com>]

* Tony Lindgren <tony@atomide.com> [230603 05:41]:
> I don't think 8250_mtk needs to do register access before and after the
> serial port registration, but if it does, then adding custom read/write
> functions can be done that do not rely on initialized port like
> serial_out().

Oh but mtk8250_runtime_suspend() calls serial_in(up, MTK_UART_DEBUG0), so
yeah if that gets called before registration is complete it causes a NULL
pointer exception. If the serial_ctrl and serial_port devices do runtime
suspend before port registration completes, things will fail.

Sounds like doing pm_runtime_resume_and_get() in mtk8250_probe() might
fix the issue. Still seems that adding a custom read function for
mtk8250_runtime_suspend() to use instead of calling serial_in() should
not be needed.

An experimental untested patch below, maye it helps?

Regards,

Tony

8< ------
diff --git a/drivers/tty/serial/8250/8250_mtk.c b/drivers/tty/serial/8250/8250_mtk.c
--- a/drivers/tty/serial/8250/8250_mtk.c
+++ b/drivers/tty/serial/8250/8250_mtk.c
@@ -588,20 +588,24 @@ static int mtk8250_probe(struct platform_device *pdev)
 	platform_set_drvdata(pdev, data);
 
 	pm_runtime_enable(&pdev->dev);
-	err = mtk8250_runtime_resume(&pdev->dev);
+	err = pm_runtime_resume_and_get(&pdev->dev);
 	if (err)
 		goto err_pm_disable;
 
 	data->line = serial8250_register_8250_port(&uart);
 	if (data->line < 0) {
 		err = data->line;
-		goto err_pm_disable;
+		goto err_pm_put;
 	}
 
 	data->rx_wakeup_irq = platform_get_irq_optional(pdev, 1);
 
+	pm_runtime_put_sync(&pdev->dev);
+
 	return 0;
 
+err_pm_put:
+	pm_runtime_put_sync(&pdev->dev);
 err_pm_disable:
 	pm_runtime_disable(&pdev->dev);
 
-- 
2.41.0