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Date: Sat, 14 Jan 2006 13:26:11 -0800
From: Sebastian <list@mindling.com>
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Subject: Getting around WRITE_DMA errors
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Hi,
Installing 6.0-RELEASE on a new machine. (Have tried 5.4 too). Using a 
PCChips M848ALU motherboard with onboard SiS
IDE controller, and a Hitachi 160gb disk.

When my disk is in UDMA6 (133) mode, FreeBSD dies painfully with many 
errors like:

  ad0: WARNING -  WRITE_DMA48 UDMA ICRC error (retrying request) 
LBA=316139999
  ad0: WARNING -  WRITE_DMA48 UDMA ICRC error (retrying request) 
LBA=316139999
  ad0: FAILURE -  WRITE_DMA48 status=51(READY,DSC,ERROR) 
error=4(ABORTED) LBA=316139999

It then panics and dumps:

  panic: initiate_write_inodeblock_ufs2: already started

If I disable dma using "set hw.ata.ata_dma=0" at boot, or simply boot in 
safe mode, it goes into PI04 mode and works fine. Also, if I change to a 
lesser UDMA value using atacontrol after boot, such as:

  # atacontrol mode ad0 UDMA4

... it also seems to behave just fine. I've tried UDMA3, UDMA4, UDMA5, 
all seemingly without errors. But when I use UDMA6, the machine 
immediately dies when the disk gets written to.

So my question:

What's the best way to tell FreeBSD to always use UDMA5 mode on that 
disk at boot time (before it attempts to use the drive)?

Thanks,
Sebastian