Re: [PATCH] tty: serial: fsl_lpuart: mark last busy before uart_add_one_port

[Alexander Stein <alexander.stein@ew.tq-group.com>]

Am Donnerstag, 8. August 2024, 16:03:25 CEST schrieb Peng Fan (OSS):
> From: Peng Fan <peng.fan@nxp.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@nxp.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?

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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