Date: Thu, 21 Feb 2002 15:08:49 -0800 (PST) From: Kelly Yancey <kbyanc@posi.net> To: Joerg Wunsch <joerg_wunsch@uriah.heep.sax.de> Cc: =?iso-8859-1?Q?G=E9rard_Roudier?= <groudier@free.fr>, <freebsd-scsi@FreeBSD.ORG> Subject: Re: RBC support patch Message-ID: <20020221150706.C89039-100000@gateway.posi.net> In-Reply-To: <20020221140554.N89039-100000@gateway.posi.net>
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Argh. Nevermind, it looks like Shimokawa-san is already on the problem.
After his patch is committed, maybe then I'll look into 10->6 conversion for
READ if anyone still thinks it is necessary.
Kelly
kbyanc@{posi.net,FreeBSD.org}
On Thu, 21 Feb 2002, Kelly Yancey wrote:
> On Thu, 21 Feb 2002, Joerg Wunsch wrote:
>
> > As Gérard Roudier wrote:
> >
> > > My understanding is that WRITE(10) is just meaningless for read-only
> > > devices, thus optionnal. But this is not worded this way in the
> > > specs.
> >
> > Yep, i thought so, too, after reading the specs a bit more carefully.
> > --
> > cheers, J"org .-.-. --... ...-- -.. . DL8DTL
>
> I stand corrected: READ(6) and READ(10) are both mandatory in SCSI2. I just
> eyeballed the WRITE commands (which are both optional) and assumed that
> applied to READ also. But on second intespection, I see that you are correct.
> Nonetheless, per Justin's suggestion, I am preparing patches to convert 6 byte
> commands to 10 byte once a device returns 'command not supported' for the 6
> byte version.
> Per recent discussion, I may try and implement 10 to 6 conversion that may
> be used if the command the DPO, FUA, and RelAdr bits are clear, the transfer
> length is under 256 blocks, and the LBA fits in 21 bits. In which case, if
> a READ(10) fails, it can fall back to READ(6) (assuming a 6 byte read hasn't
> already failed). In which case, we can determine which size we prefer to try
> first based on SCSI revision (>=2 try 10 byte commands first, <2 try 6 byte
> commands first) with fallback should that fail. But note that while
> 6 to 10 appears fairly straightforward, currently I am only considering
> converting 10 byte reads to 6 byte reads right now. I'm not too comfortable
> about the number of restrictions involved to downgrade a later command set to
> an earlier one (as demonstrated by the READ criteria I listed above).
> This is all getting a bit more complicated than I had originally planned.
> Still doable, it's just going to take me a little longer. Please hold off on
> suggesting any more cases/features until I post patches. :) Thanks,
>
> Kelly
> kbyanc@{posi.net,FreeBSD.org}
>
>
>
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--
Kelly Yancey - kbyanc@posi.net - Belmont, CA
Lead Engineer, Backplane, Inc. http://www.backplane.com/
Maintainer, BSD Driver Database http://www.posi.net/freebsd/drivers/
Coordinator, Team FreeBSD http://www.posi.net/freebsd/Team-FreeBSD/
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