From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hannes Reinecke Subject: Re: [PATCH] megaraid_sas: Enable shared tag map Date: Thu, 02 Oct 2014 14:14:19 +0200 Message-ID: <542D419B.5080406@suse.de> References: <1411991272-129962-1-git-send-email-hare@suse.de> <542C4D33.2030401@hp.com> <20141001211003.GA24820@infradead.org> <542CF5E8.3030601@suse.de> <1412251542.6343.6.camel@jarvis> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from cantor2.suse.de ([195.135.220.15]:33175 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751283AbaJBMOV (ORCPT ); Thu, 2 Oct 2014 08:14:21 -0400 In-Reply-To: <1412251542.6343.6.camel@jarvis> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: James Bottomley Cc: "linux-scsi@vger.kernel.org" , "hch@infradead.org" , "webbnh@hp.com" On 10/02/2014 02:05 PM, James Bottomley wrote: > On Thu, 2014-10-02 at 08:51 +0200, Hannes Reinecke wrote: >> On 10/01/2014 11:10 PM, Christoph Hellwig wrote: >>> On Wed, Oct 01, 2014 at 02:51:31PM -0400, Webb Scales wrote: >>>> Hannes, >>>> >>>> In megasas_change_queue_type(), is it possible for sdev->queue_dep= th to be >>>> greater than 256? >>>> >>>> Unless I'm misunderstanding the SCSI code, we can request a >>>> queue-depth/tag-map-size which is greater than 256, but, since the >>>> scsi_cmnd::tag field is an unsigned char, depths greater than 256 = may >>>> overflow the field when high-numbered tags are used...do I have th= at right? >>> >>> Yes, we really need to increase the size of the tag field. SAM all= ows >>> a transport specific limit of up to 64 _bytes_ for it, although I d= on't >>> know implementation that large. Given that the block layer can gen= erate >>> up to 32-bit tags both for the old blk-tag.c code and the new >>> blk-mq-tag.c version it would be good to use a u32 there. Can you = send >>> me a patch? >>> >> Weeelll ... >> >> I'm afraid it's not _that_ easy. >> SCSI-II tagged queueing has some specific tag values: >> >> #define SIMPLE_QUEUE_TAG 0x20 >> #define HEAD_OF_QUEUE_TAG 0x21 >> #define ORDERED_QUEUE_TAG 0x22 >> >> drivers/scsi/vmw_pvscsi.c: >> e->tag =3D SIMPLE_QUEUE_TAG; >> if (sdev->tagged_supported && >> (cmd->tag =3D=3D HEAD_OF_QUEUE_TAG || >> cmd->tag =3D=3D ORDERED_QUEUE_TAG)) >> e->tag =3D cmd->tag; >=20 > A SCSI-2 tag is a SPI two byte message. The first byte is the messag= e > type. The values you have above identify the message type for simple= , > ordered and head of queue tags. The *second* byte is the tag value. >=20 > See page 55 and 56 of the SCSI-2 standard. There's no connection (or > shouldn't be) between the message type and the tag value, so it looks > like a bug in the pvscsi driver. >=20 It is. I've already sent a patch. But that just proves the scmd->tag is essentially a duplicate and we should be removing it. Cheers, Hannes --=20 Dr. Hannes Reinecke zSeries & Storage hare@suse.de +49 911 74053 688 SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 N=C3=BCrnberg GF: J. Hawn, J. Guild, F. Imend=C3=B6rffer, HRB 16746 (AG N=C3=BCrnberg= ) -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html