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

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Message-ID: <53C6AAE1.7090802@linutronix.de>
Date:	Wed, 16 Jul 2014 18:40:01 +0200
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	balbi@...com
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 07/16/2014 06:06 PM, Felipe Balbi wrote:

>>> well, other than in probe and other functions which need to
>>> make sure clocks are on, but it seems unnecessary to
>>> enable/disable in every function.
>> 
>> What do you have in mind? Do you plan to let the uart on while
>> the minicom is attached but is doing nothing? In that case,
>> ->startup() and ->shutdown() should be enough.
> 
> no the idea was to keep it on for as long as it's transferring 
> characters and idle it otherwise, if that can't be done easily,
> then I guess your way is the only way.

But maybe we have to add some additional logic here to keep it up for
the transfer. I've been just (maybe over)thinking: If you send 300
bytes over DMA via 300 baud it should take 10 seconds. The PM-timeout
could hit before the transfer is complete.
Same thing with hw-flowcontrol where you could get stalled for a few
seconds.
However it doesn't seem to be a problem in current omap-serial driver.

> cheers

Sebastian
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