linux-kernel - Re: [PATCH 3/6] tty: serial: 8250 core: add runtime pm

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Date:	Wed, 9 Jul 2014 23:28:12 -0700
From:	Tony Lindgren <tony@...mide.com>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:	linux-omap@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Felipe Balbi <balbi@...com>, linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org, mika.westerberg@...ux.intel.com
Subject: Re: [PATCH 3/6] tty: serial: 8250 core: add runtime pm

* Sebastian Andrzej Siewior <bigeasy@...utronix.de> [140709 10:52]:
> While comparing the OMAP-serial and the 8250 part of this I noticed that
> the the latter does not use runtime-pm. Here are the pieces. It is
> basically a get before first register access and a last_busy + put after
> last access.
> If I understand this correct, it should do nothing as long as
> pm_runtime_use_autosuspend() + pm_runtime_enable() isn't invoked on the
> device.
...

> --- a/drivers/tty/serial/8250/8250_core.c
> +++ b/drivers/tty/serial/8250/8250_core.c
> @@ -571,7 +573,17 @@ static void serial8250_set_sleep(struct uart_8250_port *p, int sleep)
>  			serial_out(p, UART_EFR, 0);
>  			serial_out(p, UART_LCR, 0);
>  		}
> +
> +		if (!device_may_wakeup(p->port.dev)) {
> +			if (sleep)
> +				pm_runtime_forbid(p->port.dev);
> +			else
> +				pm_runtime_allow(p->port.dev);
> +		}
>  	}
> +out:
> +	pm_runtime_mark_last_busy(p->port.dev);
> +	pm_runtime_put_autosuspend(p->port.dev);
>  }

The device_may_wakeup logic here is wrong as I described in the
earlier thread. For runtime PM, the wake-up events should be
always enabled. So the device_may_wakeup checks should be only
done for suspend and resume.

Regards,

Tony
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