linux-kernel - Re: [PATCH v7] 8250-core based serial driver for OMAP + DMA

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Date:	Mon, 18 Aug 2014 11:15:17 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	Tony Lindgren <tony@...mide.com>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
CC:	Lennart Sorensen <lsorense@...lub.uwaterloo.ca>,
	linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-omap@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	balbi@...com, Vinod Koul <vinod.koul@...el.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v7] 8250-core based serial driver for OMAP + DMA

On 08/15/2014 04:28 PM, Tony Lindgren wrote:
> * Sebastian Andrzej Siewior <bigeasy@...utronix.de> [140815 12:16]:
>> On 08/15/2014 08:17 PM, Lennart Sorensen wrote:
>>
>>> Are you saying that with the new driver you have to respond to the RX
>>> irq faster than before to avoid overflows?  It is not quite clear.
>>
>> Yes. The irq fires 46 bytes giving you 16 bytes buffer before overflow
>> vs 63 bytes buffer the old one had.
>>
>>> I do think 40000 interrupts to handle 40000 bytes of date does seem a
>>> tad inefficient, so dropping to 854 looks a lot nicer.  Was the omap
>>> driver not using the fifo trigger levels at all?
>>
>> It configured the trigger levels to 1 for RX and 16 for TX.
> 
> Hmm that weird RX trigger level is a workaround for lost characters.
> 
> See commit 0ba5f66836 (tty: serial: OMAP: use a 1-byte RX FIFO
> threshold in PIO mode :)

That commit looks like it should have been specific to the silicon
exhibiting the rx timeout bug.

Regards,
Peter Hurley

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