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

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Message-ID: <570BE48F.60801@hurleysoftware.com>
Date:	Mon, 11 Apr 2016 10:53:19 -0700
From:	Peter Hurley <peter@...leysoftware.com>
To:	John Ogness <john.ogness@...utronix.de>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Tony Lindgren <tony@...mide.com>, nsekhar@...com,
	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

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:
>>> It has been observed that the TX-DMA can stall
>>
>> Does this happen on any other OMAP part besides am335x?
>> I looked back over the LKML history of this and didn't see
>> any other design implicated in this problem.
> 
> I just ran the tests again using 4.6-rc2. I am able to reproduce the
> dma-tx stall with am335x/edma and dra7/sdma.

I thought we already established sdma was not to be used since
the hardware does not actually support pausing without data loss.

http://www.spinics.net/lists/linux-serial/msg18503.html


So I'm wondering if we're carrying all this extra DMA complexity
and workarounds for just am335x?


> Note: To achieve the stall, both the delayed_restore and the
>       rx_dma_broken features of the mainline 8250_omap driver needed to
>       be removed.
> 
> John Ogness
>