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

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Message-ID: <53C942F1.2000408@hurleysoftware.com>
Date:	Fri, 18 Jul 2014 11:53:21 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	balbi@...com, Sebastian Andrzej Siewior <bigeasy@...utronix.de>
CC:	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 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.

Regards,
Peter Hurley


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