linux-kernel - Re: [PATCH] libsas: support NCQ for SATA disks

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Message-ID: <45340A62.7050406@us.ibm.com>
Date:	Mon, 16 Oct 2006 17:40:34 -0500
From:	Brian King <brking@...ibm.com>
To:	"Darrick J. Wong" <djwong@...ibm.com>
CC:	linux-scsi <linux-scsi@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Alexis Bruemmer <alexisb@...ibm.com>,
	Mike Anderson <andmike@...ibm.com>
Subject: Re: [PATCH] libsas: support NCQ for SATA disks

Darrick J. Wong wrote:
> This patch adds SATAII NCQ support to libsas.  Both the use_ncq and the
> dma_xfer flags in ata_task must be set for NCQ to work correctly on the
> Adaptec SAS controller.  The rest of the patch adds ATA_FLAG_NCQ to
> sata_port_info and sets up ap->scsi_host so that ata_setup_ncq doesn't
> crash.  Please note that this patch is against the aic94xx-sas git tree,
> not scsi-misc.  Thanks also to James Bottomley for providing an earlier
> version of this patch from which to work.


> @@ -875,6 +881,7 @@ int sas_target_alloc(struct scsi_target 
>  
>  		ap->private_data = found_dev;
>  		ap->cbl = ATA_CBL_SATA;
> +		ap->scsi_host = shost;
>  		found_dev->sata_dev.ap = ap;
>  	}
>  

This doesn't look like the right fix for the oops you were seeing. The
SAS usage of libata has ap->scsi_host as NULL, which indicates that
libata does not own the associated scsi_host. I'm concerned you may
have broken some other code path by making this change. I think the correct
fix may require removing the dependence of ap->scsi_host from
ata_dev_config_ncq. 

Brian

-- 
Brian King
eServer Storage I/O
IBM Linux Technology Center
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