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

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Date:	Mon, 18 Aug 2014 11:37:57 -0500
From:	Felipe Balbi <balbi@...com>
To:	Peter Hurley <peter@...leysoftware.com>
CC:	Tony Lindgren <tony@...mide.com>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	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 Mon, Aug 18, 2014 at 11:15:17AM -0400, Peter Hurley wrote:
> 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.

yeah, I'll agree with that.

-- 
balbi

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