linux-kernel - Re: [PATCH v2 0/6] atmel_serial: Cleanups, irq handler splitup & DMA

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Date:	Wed, 19 Dec 2007 23:13:53 +0100
From:	"Ulf Samuelsson" <ulf@...el.com>
To:	"Haavard Skinnemoen" <hskinnemoen@...el.com>,
	"Andrew Victor" <linux@...im.org.za>
Cc:	"Russell King" <linux@....linux.org.uk>,
	"Haavard Skinnemoen" <hskinnemoen@...el.com>,
	<kernel@...32linux.org>, <linux-kernel@...r.kernel.org>,
	"Remy Bohmer" <linux@...mer.net>,
	<linux-arm-kernel@...ts.arm.linux.org.uk>
Subject: Re: [PATCH v2 0/6] atmel_serial: Cleanups, irq handler splitup & DMA

| The following patchset cleans up the atmel_serial driver a bit,
| moves a significant portion of the interrupt handler into a tasklet,
| and adds DMA support. This is the result of a combined effort by Chip
| Coldwell, Remy Bohmer and me. The patches should apply cleanly onto
| Linus' latest git tree.
| 
| With DMA, I see transfer rates around 92 kbps when transferring a big
| file using ZModem (both directions are roughly the same.)
| 

The start and stop bits will use 20 % of the bit rate so the
teoretical max throughput at 115,200 BAUD is 115,200 * 0,8 = 92160 bps.

What would be interesting is to figure out if we can get reliable
transmission at higher frequencies - 230/460/921 kbps.

| Note that break and error handling doesn't work too well with DMA
| enabled. This is a common problem with all the efforts I've seen
| adding DMA support to this driver (including my own). The PDC error
| handling also accesses icount without locking. I'm tempted to just
| ignore the problem for now and hopefully come up with a solution
| later.

Have told the guys responsible for the USART IP block we
need to improve the H/W for error control for the last 3-4 years.
Why not at 120000 gates/sq mm, add error counters???

Best Regards
Ulf Samuelsson
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