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

Boaz Harrosh
2009-04-22T12:16:18Z

On 04/22/2009 12:23 PM, Jeff Garzik wrote:
> 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
>

Could the master/slave be simply solved by emulating a SCSI LUN
for example below is my machine today:
[]$ lsscsi
[0:0:0:0] disk ATA ST3160023A 3.01 /dev/sda
[1:0:0:0] cd/dvd _NEC DVD_RW ND-3550A 1.05 /dev/sr0
[4:0:0:0] disk ATA WDC WD1600JS-60M 10.0 /dev/sdb

the /dev/sda and /dev/sr0 share a master/slave wide cable (sdb is sata)

it could be made to scan as:
[]$ lsscsi
[0:0:0:0] disk ATA ST3160023A 3.01 /dev/sda
[0:0:0:1] cd/dvd _NEC DVD_RW ND-3550A 1.05 /dev/sr0
[1:0:0:0] disk ATA WDC WD1600JS-60M 10.0 /dev/sdb

So we need to emulate the REPORT_LUN (or what ever else) to return
two LUNs. Or do you want to report a separate target for the master/slave?

Thanks
Boaz