Re: [PATCH v1 2/2] tty: serial: 8250_dw: Keep init pinctrl state until first open

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

On Mon, Aug 10, 2026 at 01:06:35PM +0000, Michał Kardaś wrote:
> When a UART port is connected to an external peripheral whose power
> domain is kept powered off until first use, transitioning the UART
> pins from the "init" state to the "default" state prematurely at probe
> completion can cause parasitic back-powering into the unpowered
> peripheral.
> 
> Ensure that on boards specifying an "init" pinctrl state for the port,
> the "init" state is preserved until the port is first opened:
> 
> 1. In dw8250_probe(), call pinctrl_keep_init_state(dev) to opt out of the
>    automatic "init" -> "default" transition at probe completion and record
>    this in data->in_init_state.
> 2. In dw8250_do_pm(), when the port is opened (state == 0), transition
>    pins from "init" to "default" if data->in_init_state is set, and clear
>    the flag.

...

>  dw8250_do_pm(struct uart_port *port, unsigned int state, unsigned int old)
>  {
> -	if (!state)
> +	struct dw8250_data *d = to_dw8250_data(port->private_data);
> +
> +	if (!state) {
>  		pm_runtime_get_sync(port->dev);
> +		if (d->in_init_state) {
> +			d->in_init_state = false;

Mistyped assignee. Should be 0.

> +			pinctrl_pm_select_default_state(port->dev);
> +		}
> +	}

Obviously the above needs a good comment in the code explaining why it is doing
that.

...

>  	if (data->data.line < 0)
>  		return data->data.line;

And a good comment explaining what you put in the commit message.

> +	data->in_init_state = pinctrl_keep_init_state(dev);

>  	platform_set_drvdata(pdev, data);
>  
>  	pm_runtime_enable(dev);

...

Wondering if this anyhow affects the future idea of the OOB wakeup for the UART
using its Rx as GPIO wake source in the suspend.

-- 
With Best Regards,
Andy Shevchenko