linux-kernel - Re: [PATCH 13/16] tty: serial: 8250

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Message-ID: <20140929095645.GC13142@linutronix.de>
Date:	Mon, 29 Sep 2014 11:56:45 +0200
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	Frans Klaver <frans.klaver@...ns.com>
Cc:	linux-serial@...r.kernel.org, tony@...mide.com,
	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	balbi@...com, linux-omap@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 13/16] tty: serial: 8250_dma: add pm runtime

* Frans Klaver | 2014-09-29 11:26:06 [+0200]:

>On Wed, Sep 10, 2014 at 09:30:08PM +0200, Sebastian Andrzej Siewior wrote:
>> There is nothing to do for RPM in the RX path. If the HW goes off then it
>> won't assert the DMA line and the transfer won't happen. So we hope that
>> the HW does not go off for RX to work (DMA or PIO makes no difference
>> here).
>> 
>> For TX the situation is slightly different. RPM is enabled on
>> start_tx(). We can't disable RPM on DMA complete callback because there
>> is still data in the FIFO which is being sent. We have to wait until
>> the FIFO is empty before we disable it.
>> For this to happen we fake a TX sent error and enable THRI. Once the
>> FIFO is empty we receive an interrupt and since the TTY-buffer is still
>> empty we "put RPM" via __stop_tx(). Should it been filed then in the
>> start_tx() path we should program the DMA transfer and remove the error
>> flag and the THRI bit.
>
>That last sentence starts out a bit messy.

This got mered so there is nothing I can do about it anymore. But I will
try to fix comments in code where and in patches that are not yet merged
(what you report :))

Sebastian
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