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

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Date:	Wed, 22 Apr 2009 17:10:55 +0200
From:	Daniela Engert <dani@...t.de>
To:	Boaz Harrosh <bharrosh@...asas.com>
CC:	Jeff Garzik <jeff@...zik.org>, linux-ide@...r.kernel.org,
	linux-scsi@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	Jens Axboe <jens.axboe@...cle.com>,
	Tejun Heo <htejun@...il.com>
Subject: Re: [PATCH] libata: rewrite SCSI host scheme to be one per ATA host

Boaz Harrosh wrote:
> 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.

>>> 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

Don't forget, there are ATAPI devices (some Sony CD burners and old 
phase-changers come into mind) which *do* have multiple LUNs sitting 
beyond the PATA port. I don't know if libata supports such setups (my 
old OS/2 driver does) but one shouldn't hijack LUNs to emulate targets.

Ciao,
   Dani
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