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

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Message-ID: <53C7EC6F.6060902@hurleysoftware.com>
Date:	Thu, 17 Jul 2014 11:31:59 -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 07/16/2014 12:06 PM, Felipe Balbi wrote:
> On Wed, Jul 16, 2014 at 05:54:56PM +0200, Sebastian Andrzej Siewior wrote:
>> On 07/16/2014 05:16 PM, Felipe Balbi wrote:

>>> I wonder if you should get_sync() on start_tx() and only
>>> put_autosuspend() at stop_tx(). I guess the outcome would be
>>> largely the same, no ?
>>
>> I just opened minicom on ttyS0 and gave a try. start_tx() was invoked
>> each time I pressed a key (sent a character). I haven't seen stop_tx()
>> even after after I closed minicom. I guess stop_tx() is invoked if you
>> switch half-duplex communication.
>
> that's bad, I expected stop to be called also after each character.

The 8250 core auto-stops tx when the tx ring buffer is empty (except
in the case of dma, where stopping tx isn't necessary).

Regards,
Peter Hurley
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