linux-kernel - Re: [PATCH 4/5] tty: serial: 8250 core: add runtime pm

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Message-ID: <20140718160209.GQ24914@saruman.home>
Date:	Fri, 18 Jul 2014 11:02:09 -0500
From:	Felipe Balbi <balbi@...com>
To:	Peter Hurley <peter@...leysoftware.com>
CC:	<balbi@...com>, Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	<linux-omap@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	Tony Lindgren <tony@...mide.com>,
	<linux-kernel@...r.kernel.org>, <linux-serial@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<mika.westerberg@...ux.intel.com>
Subject: Re: [PATCH 4/5] tty: serial: 8250 core: add runtime pm

On Fri, Jul 18, 2014 at 11:53:21AM -0400, Peter Hurley wrote:
> On 07/18/2014 11:31 AM, Felipe Balbi wrote:
> >On Fri, Jul 18, 2014 at 10:35:10AM +0200, Sebastian Andrzej Siewior wrote:
> >>>On 07/17/2014 06:18 PM, Felipe Balbi wrote:
> >>>
> >>>>> >>No, this is okay. If you look, it checks for "up->ier &
> >>>>> >>UART_IER_THRI". On the second invocation it will see that this
> >>>>> >>bit is already set and therefore won't call get_sync() for the
> >>>>> >>second time. That bit is removed in the _stop_tx() path.
> >>>> >
> >>>> >oh, right. But that's actually unnecessary. Calling
> >>>> >pm_runtime_get() multiple times will just increment the usage
> >>>> >counter multiple times, which means you can call __stop_tx()
> >>>> >multiple times too and everything gets balanced, right ?
> >>>
> >>>No. start_tx() will be called multiple times but only the first
> >>>invocation invoke pm_runtime_get(). Now I noticed that I forgot to
> >right, but that's unnecessary. You can pm_runtime_get() every time
> >start_tx() is called. Just make sure to put everytime stop_tx() is
> >called too.
> 
> The interface is asymmetric.
> 
> start_tx() may be invoked multiple times for which only 1 interrupt
> will occur, and thus only invoke __stop_tx() once.

alright, thanks for the info.

-- 
balbi

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