From: James Bottomley <James.Bottomley@SteelEye.com>
To: Hannes Reinecke <hare@suse.de>
Cc: SCSI Mailing List <linux-scsi@vger.kernel.org>
Subject: Re: Fallback sequence in scsi_transport_spi
Date: Mon, 25 Jul 2005 08:19:32 -0400 [thread overview]
Message-ID: <1122293972.5084.4.camel@mulgrave> (raw)
In-Reply-To: <42E4A327.90005@suse.de>
On Mon, 2005-07-25 at 10:30 +0200, Hannes Reinecke wrote:
> it appears that the fallback sequence in
> scsi_transport_spi.c:spi_dv_retrain()
> is somewhat incorrect.
>
> According to SPI-3 (spi3r14, actually), the flags DT, IU, and QAS can be
> set in the following order of precedence (Table 55, p 155):
> - DT
> - IU
> - QAS
Actually, this is superceded by spi4 and 5. QAS is now optional for any
transfer agreement.
> However, the fallback routine in spi_dv_retrain first unsets IU, _then_
> QAS, and ignoring DT entirely. This smells a bit fishy.
> Any reasons for this?
DT is theoretically a more stable transfer mechanism in the face of line
noise than ST, so if the drive supports it, it makes some sense to back
down the periods still retaining DT if possible. DT also mandates data
group transfers if IU isn't mandated, so it's a safer protocol at
detecting errors as well.
James
prev parent reply other threads:[~2005-07-25 12:19 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-07-25 8:30 Fallback sequence in scsi_transport_spi Hannes Reinecke
2005-07-25 12:19 ` James Bottomley [this message]
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