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

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Date:   Sat, 3 Jun 2023 09:35:33 +0300
From:   Tony Lindgren <tony@...mide.com>
To:     John Ogness <john.ogness@...utronix.de>
Cc:     Chen-Yu Tsai <wenst@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...el.com>,
        Dhruva Gole <d-gole@...com>,
        Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
        Johan Hovold <johan@...nel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Vignesh Raghavendra <vigneshr@...com>,
        linux-omap@...r.kernel.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
        Nícolas F. R. A. Prado 
        <nfraprado@...labora.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH v12 1/1] serial: core: Start managing serial controllers
 to enable runtime PM

* Tony Lindgren <tony@...mide.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