linux-kernel - Re: omap uart + dma issues (Re: [PATCH] tty: serial: 8250

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Date:	Wed, 13 Apr 2016 16:41:23 +0530
From:	Sekhar Nori <nsekhar@...com>
To:	Peter Hurley <peter@...leysoftware.com>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	John Ogness <john.ogness@...utronix.de>,
	Tony Lindgren <tony@...mide.com>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<linux-kernel@...r.kernel.org>, <linux-serial@...r.kernel.org>,
	<linux-omap@...r.kernel.org>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: Re: omap uart + dma issues (Re: [PATCH] tty: serial: 8250_omap: do
 not defer termios changes)

On Wednesday 13 April 2016 05:30 AM, Peter Hurley wrote:

>>> - generates spurious uart interrupt for every rx dma transaction
>>>   (ie., necessitates acking every UART interrupt, even UART_IIR_NO_INT)
>>>   _Even with this workaround_, it still generates spurious interrupt warning
>>>   which shuts off interrupts for several ms while logging the error
>>>   message to the console, virtually guaranteeing lost data.
>>
>> as I wrote in my other email I think RDI should be disabled with DMA
> 
> 
> I'll test to see if disabling RDI eliminates the UART_IIR_NO_INT spurious
> interrupts.
> 
>> according the Intel manual and I *think* someone here reported that
>> they see the same problem.
> 
> Let's confirm with the Intel folks that this is true, which would argue
> for using the omap-style rx dma flow.

Andy Shevchenko pointed this out here: https://lkml.org/lkml/2016/2/23/588

Regards,
Sekhar