Re: [PATCH] libata: rewrite SCSI host scheme to be one per ATA host

Jeff Garzik
2009-04-22T09:23:49Z

Jeff Garzik wrote:
> Currently, libata creates a Scsi_Host per port. This was originally
> done to leverage SCSI's infrastructure to arbitrate among master/slave
> devices, but is not needed for most modern SATA controllers. And I
> _think_ it is not needed for master/slave if done properly, either.

BTW note the above, with regards to the libata SCSI->block conversion.
libata currently relies on SCSI for some amount of generic device
arbitration, in several situations (see ->qc_defer,
SCSI_MLQUEUE_.*_BUSY). libata expects SCSI to be intelligent and not
starve devices, etc.

> I was able to successfully boot the following patch on
> AHCI/x86-64/Fedora.
>
> It may work with other controllers -- TRY AT YOUR OWN RISK. It will
> probably fail for master/slave configurations, and SAS & PMP also
> need looking at. It yielded this lsscsi output on my AHCI box:
>
> [0:0:0:0] disk ATA ST3500320AS SD15 /dev/sda
> [0:2:0:0] disk ATA G.SKILL 128GB SS 02.1 /dev/sdb
> [0:5:0:0] cd/dvd PIONEER BD-ROM BDC-202 1.04 /dev/sr0

For comparison, here is unmodified 2.6.30-rc3:

[jgarzik@bd ~]$ lsscsi
[0:0:0:0] disk ATA ST3500320AS SD15 /dev/sda
[2:0:0:0] disk ATA G.SKILL 128GB SS 02.1 /dev/sdb
[5:0:0:0] cd/dvd PIONEER BD-ROM BDC-202 1.04 /dev/sr0