linux-kernel - RE: [PATCH] tty: serial: fsl_lpuart: mark last busy before uart_add_one

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Message-ID:
 <PAXPR04MB8459C70644E1F1852A0782FB88BA2@PAXPR04MB8459.eurprd04.prod.outlook.com>
Date: Fri, 9 Aug 2024 07:09:33 +0000
From: Peng Fan <peng.fan@....com>
To: Alexander Stein <alexander.stein@...tq-group.com>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"jirislaby@...nel.org" <jirislaby@...nel.org>,
	"u.kleine-koenig@...gutronix.de" <u.kleine-koenig@...gutronix.de>, "Peng Fan
 (OSS)" <peng.fan@....nxp.com>
CC: Sherry Sun <sherry.sun@....com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "linux-serial@...r.kernel.org"
	<linux-serial@...r.kernel.org>
Subject: RE: [PATCH] tty: serial: fsl_lpuart: mark last busy before
 uart_add_one_port

> Subject: Re: [PATCH] tty: serial: fsl_lpuart: mark last busy before
> uart_add_one_port
> 
> Am Donnerstag, 8. August 2024, 16:03:25 CEST schrieb Peng Fan (OSS):
> > From: Peng Fan <peng.fan@....com>
> >
> > With "earlycon initcall_debug=1 loglevel=8" in bootargs, kernel
> > sometimes boot hang. It is because normal console still is not ready,
> > but runtime suspend is called, so early console putchar will hang in
> > waiting TRDE set in UARTSTAT.
> >
> > The lpuart driver has auto suspend delay set to 3000ms, but during
> > uart_add_one_port, a child device serial ctrl will added and probed
> > with its pm runtime enabled(see serial_ctrl.c).
> > The runtime suspend call path is:
> > device_add
> >      |-> bus_probe_device
> >            |->device_initial_probe
> > 	           |->__device_attach
> >                          |-> pm_runtime_get_sync(dev->parent);
> > 			 |-> pm_request_idle(dev);
> > 			 |-> pm_runtime_put(dev->parent);
> >
> > So in the end, before normal console ready, the lpuart get runtime
> > suspended. And earlycon putchar will hang.
> >
> > To address the issue, mark last busy just after pm_runtime_enable,
> > three seconds is long enough to switch from bootconsole to normal
> > console.
> >
> > Fixes: 43543e6f539b ("tty: serial: fsl_lpuart: Add runtime pm
> > support")
> > Signed-off-by: Peng Fan <peng.fan@....com>
> > ---
> >  drivers/tty/serial/fsl_lpuart.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/drivers/tty/serial/fsl_lpuart.c
> > b/drivers/tty/serial/fsl_lpuart.c index 615291ea9b5e..77efa7ee6eda
> > 100644
> > --- a/drivers/tty/serial/fsl_lpuart.c
> > +++ b/drivers/tty/serial/fsl_lpuart.c
> > @@ -2923,6 +2923,7 @@ static int lpuart_probe(struct
> platform_device *pdev)
> >  	pm_runtime_set_autosuspend_delay(&pdev->dev,
> UART_AUTOSUSPEND_TIMEOUT);
> >  	pm_runtime_set_active(&pdev->dev);
> >  	pm_runtime_enable(&pdev->dev);
> > +	pm_runtime_mark_last_busy(&pdev->dev);
> 
> This change looks sensible to me. Is maybe [1] addressing the same
> issue at a different level?

If the lpuart driver is built as module, [1] could not resolve the issue.

And if lpuart driver is built as module, [1] might break earlycon.
of_clk_drop_stdout_clocks disables clocks, but lpuart driver not
insmod at that time.

The current patch is simple and easy for backporting to stable
tree. [1] is not suitable for backporting to stable tree.

Regards,
Peng.

> 
> Best regards,
> Alexander
> 
> [1] https://lore.kernel.org/all/20240808-gs101-non-essential-clocks-2-v6-0-e91c537acedc@linaro.org/
> 
> >
> >  	ret = lpuart_global_reset(sport);
> >  	if (ret)
> >
> 
> 
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