Date: Fri, 15 May 1998 18:10:06 -0600 (MDT) From: "Justin T. Gibbs" <gibbs@narnia.plutotech.com> To: Matthew Jacob <mjacob@feral.com> Cc: scsi@FreeBSD.ORG Subject: Re: CAM flags && tagging... Message-ID: <199805160010.SAA24354@narnia.plutotech.com> In-Reply-To: <355CC257.4F4AE38D@feral.com>
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In article <355CC257.4F4AE38D@feral.com> you wrote: > I notice there's a flag in the CCB header that enables tag > action. I haven't got the SCSI-3 CAM2 spec in front of me, > but would it specify (or could we extend) to specify what > *kind* of tagging is preferred? I'm sewing up the ISP driver > for the FreeBSD/CAM, and now that I'm going to really depend > upon CAM_TAG_ACTION_ENABLE as a flag, I'd also like to know > whether the caller prefers HEAD OF QUEUE, SIMPLE, or ORDERED. If the CAM_TAG_ACTION_VALID flag is set, then the tag_action field of the CCB is valid. This field indicates the type of tag to send. tag_action will be set to one of the SCSI-II specified tag message values (0x20, 0x21, 0x22). The da driver makes use of this feature to prevent tag starvation and also to convert buffers set with the B_ORDERED flag into ordered tagged transactions. > BTW- as a side note- for the Qlogic 2100 and FCP-SCSI, you > cannot disable tags (you always have to have *some* tag is what > I read in the spec), so that defaults to SIMPLE when tagging > is otherwise disabled (Bob- do you want to comment)? Hmm. I didn't think that tags were mandatory for any SCSI transport. The CAM code currently leaves tags disabled (won't set CAM_TAG_ACTION_VAlID bit) unless the controller indicates that it supports it, we have completed our inquiry fetch and it indicates the end device supports tagged queuing, and the device control page either is not supported or does not have the DQUE bit set. > -matt -- Justin To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message
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