Odd ada(4) failures when trying using USB scanner

[Alexander Motin]

Michael Reifenberger wrote:
> I'm using -current as of r202157.
> 
> When attaching an epson USB scanner and trying to `scanimage -L`
> I get a freeze for some time and the following console logs:
> ...
> ata1: FAILURE - odd-sized DMA transfer attempt 5 % 2
> ata1: setting up DMA failed

I would say that scanner application tries to probe all CAM devices,
looking for scanner. While doing it, it uses SCSI/ATAPI commands with
odd-sized transfer sizes. It causes errors from ata(4) and triggers bug
in IXP700 AHCI controller. Odd-sized requests are generally not
supported by ATA/SATA. Second problem is in work now.

-- 
Alexander Motin