Re: sata_via: write errors on SATA drive connected to VT6421

[Jeff Garzik <jgarzik@pobox.com>]

Landry Breuil wrote:
> Hi,
> 
> i encounter a very similar problem as reported in
> http://marc.info/?l=linux-kernel&m=118764381013943&w=2, but with a SATA
> disk. Trying to transfer 250Gb (mostly small files) from a SATA disk
> (ata1/sda) to another (ata2/sdb), both plugged on the VT6421 card, after
> some dozens of seconds the controler bails out and degrades write performance
> (UDMA133->UDMA100->UDMA33...)
> 
> kernel: ata2.00: limiting speed to UDMA/33:PIO4
> kernel: ata2.00: exception Emask 0x12 SAct 0x0 SErr 0x1400500 action 0x2 frozen
> kernel: ata2: SError: { UnrecovData Proto Handshk TrStaTrns }
> kernel: ata2.00: cmd 35/00:00:07:c6:f4/00:04:07:00:00/e0 tag 0 dma 524288 out
> kernel:          res 40/00:b0:27:1d:dc/84:00:07:00:00/e0 Emask 0x16 (ATA bus error)

Like Robert noted, this is the hardware complaining that it has found a 
hardware error.

"SErr" stands for SATA SError register value.  That is a value read 
directly from hardware, which indicates one or more problems.  Here is 
some more info:
http://ata.wiki.kernel.org/index.php/Libata_error_messages#SATA_SError_expansion

When libata sees a bunch of hardware problems, it tries the only things 
it can do to attempt progress in that situation:  reset the hardware, 
and slow down data transfer in an attempt to avoid errors again.

	Jeff