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Date: Fri, 31 May 2024 08:01:55 +0300
From: Tony Lindgren <tony.lindgren@linux.intel.com>
To: Douglas Anderson <dianders@chromium.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Jiri Slaby <jirislaby@kernel.org>,
	Johan Hovold <johan+linaro@kernel.org>,
	Yicong Yang <yangyicong@hisilicon.com>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= <u.kleine-koenig@pengutronix.de>,
	John Ogness <john.ogness@linutronix.de>,
	linux-arm-msm@vger.kernel.org, Tony Lindgren <tony@atomide.com>,
	Guanbing Huang <albanhuang@tencent.com>,
	Thomas Gleixner <tglx@linutronix.de>, linux-kernel@vger.kernel.org,
	linux-serial@vger.kernel.org
Subject: Re: [PATCH v2] serial: port: Don't block system suspend even if
 bytes are left to xmit
Message-ID: <ZllZw3g8pF82lf8D@tlindgre-MOBL1>
References: <20240530084841.v2.1.I2395e66cf70c6e67d774c56943825c289b9c13e4@changeid>
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In-Reply-To: <20240530084841.v2.1.I2395e66cf70c6e67d774c56943825c289b9c13e4@changeid>

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@linux.intel.com>