linux-kernel - Re: [PATCH] tty: serial: 8250_omap: do not defer termios changes

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Message-ID: <572892E1.90600@ti.com>
Date:	Tue, 3 May 2016 17:30:33 +0530
From:	Vignesh R <vigneshr@...com>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Peter Hurley <peter@...leysoftware.com>,
	John Ogness <john.ogness@...utronix.de>,
	Tony Lindgren <tony@...mide.com>, <nsekhar@...com>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<linux-kernel@...r.kernel.org>, <linux-serial@...r.kernel.org>,
	<linux-omap@...r.kernel.org>
Subject: Re: [PATCH] tty: serial: 8250_omap: do not defer termios changes

Hi,

On 04/12/2016 10:33 PM, Sebastian Andrzej Siewior wrote:
> On 04/11/2016 10:10 PM, Peter Hurley wrote:
>> On 04/11/2016 11:31 AM, Sebastian Andrzej Siewior wrote:
>>> On 04/11/2016 07:53 PM, Peter Hurley wrote:
>>>> On 04/11/2016 01:18 AM, John Ogness wrote:
>>>>> On 2016-04-05, Peter Hurley <peter@...leysoftware.com> wrote:
>>>>>> On 03/31/2016 01:41 AM, John Ogness wrote:

[...]

>> *am335x*
> 
> I am not sure if the limitations are based on the DMA engine or the
> 
>> - requires write to tx fifo to trigger tx dma (ie. OMAP_DMA_TX_KICK
>>   workaround necessitating completely different tx dma completion handler)
> 
> This one for instance I don't see on BeagleBoard xM / omap36xx and
> DRA7x. Both (not affected) use SDMA instead EDMA. It would be
> interesting to see if DRA7x is affected once it uses EDMA.
> 

8250 UART DMA works fine with EDMA as the DMA engine.
As per my testing, am335x + EDMA, am437x + EDMA, dra7xx + EDMA and
dra72x + EDMA require OMAP_DMA_TX_KICK quirk. However when using SDMA
OMAP_DMA_TX_KICK is not needed (I tested on dra7xx platform). So, it can
be concluded that when using EDMA with 8250 UART tx kick is needed.



-- 
Regards
Vignesh