[9fans] Enabling DMA causes newlines on console

[zfolkerts@starcenter.tn.org]

Hi,

If I enable DMA on my disks I get blank lines on the console whenever
I do disk I/O. Basically this prevents me from using rio while any
I/O is happening. I think there may be a blank message echoed to the
console in the IDE driver or somewhere. This does not happen if I do
not have DMA enabled. This seems to happen even if I only enable DMA on
one disk. It also seems to happen on both the onboard and offboard
controllers. I have not yet done extensive testing(I set up this server
yesterday), so I am unsure if this happens only with reads, writes or
both.

My setup is as follows:
The onboard IDE is a VIA, it is one of the VT82C69xx chipsets.
	(I am not at the machine now, and I don't remember the exact #)
The offboard IDE is a Promise Ultra 100.

My disk layout looks like this:
	/dev/sdC0/fs      1Gb kfs (What I am currently booting from)
	/dev/sdC0/fossil  20Gb fossil
	/dev/fs/isect0    1Gb index
		/dev/sdE0/isect0
		/dev/sdF0/isect0
	/dev/fs/arenas0   17Gb arena
		/dev/sdE0/arenas0
		/dev/sdF0/arenas0

So if I do this:
# for (i in sdC0 sdE0 sdF0)
	echo 'dma on' > /dev/^$i^/ctl
# con -l /srv/fscons
prompt:
main: snap -a

A couple of seconds later, when the data is sent off to venti, I will get
blank lines scroll through the center of my display, as if a message were
being printed on the console, but no text appears. Any ideas as to the
cause/prevention of this behavior? I never had DMA enabled on the
previous fossil/venti fileserver that I had, so I have only seen this
happen on this box. None of my other machines running Plan 9 have disks
in them, so I have only seen this happen on this machine.

Thanks,
Zack Folkerts