Re: [PATCH v2] serial: port: Don't block system suspend even if bytes are left to xmit

[Tony Lindgren]

On Thu, May 30, 2024 at 08:48:46AM -0700, Douglas Anderson wrote:
> The DEFINE_RUNTIME_DEV_PM_OPS() used by the serial_port code means
> that the system suspend function will be pm_runtime_force_suspend().
> In pm_runtime_force_suspend() we can see that before calling the
> runtime suspend function we'll call pm_runtime_disable(). This should
> be a reliable way to detect that we're called from system suspend and
> that we shouldn't look for busyness.

OK makes sense, one comment below though.

> --- a/drivers/tty/serial/serial_port.c
> +++ b/drivers/tty/serial/serial_port.c
> @@ -64,6 +64,16 @@ static int serial_port_runtime_suspend(struct device *dev)
>  	if (port->flags & UPF_DEAD)
>  		return 0;
>  
> +	/*
> +	 * We only want to check the busyness of the port if runtime PM is
> +	 * enabled. Specifically runtime PM will be disabled by
> +	 * pm_runtime_force_suspend() during system suspend and we don't want
> +	 * to block system suspend even if there is data still left to
> +	 * transmit. We only want to block regular runtime PM transitions.
> +	 */
> +	if (!pm_runtime_enabled(dev))
> +		return 0;
> +

How about change the comment a bit to describe why this happens so it's
easy to remember the next time looking at the code. I'd suggest just
something like this:

Nothing to do on pm_runtime_force_suspend(), see DEFINE_RUNTIME_DEV_PM_OPS

Other than that:

Reviewed-by: Tony Lindgren <tony.lindgren@xxxxxxxxxxxxxxx>