From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stefan Richter Subject: Re: [PATCH] ieee1394: sbp2: lower block queue alignment requirement Date: Mon, 15 Jan 2007 21:02:14 +0100 (CET) Message-ID: References: <1168802387.2780.1.camel@mulgrave.il.steeleye.com> <59ad55d30701151139w6176e785g53404d7b3a42ce6e@mail.gmail.com> Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from einhorn.in-berlin.de ([192.109.42.8]:50434 "EHLO einhorn.in-berlin.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751453AbXAOUCl convert rfc822-to-8bit (ORCPT ); Mon, 15 Jan 2007 15:02:41 -0500 In-Reply-To: <59ad55d30701151139w6176e785g53404d7b3a42ce6e@mail.gmail.com> Content-Disposition: INLINE Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: =?iso-8859-1?Q?Kristian_H=F8gsberg?= Cc: James Bottomley , linux1394-devel@lists.sourceforge.net, linux-scsi@vger.kernel.org On 15 Jan, Kristian H=F8gsberg wrote: > On 1/14/07, Stefan Richter wrote: >> OK, thanks. I will keep the explicit setting of the mask then. >> I actually think that everything should work just fine with 4 bytes >> alignment, but the SBP-2 spec mentiones 8 bytes alignment for the S/= G >> tables. So maybe device firmwares will expect it that way even thou= gh >> IEEE 1394 doesn't impose such a restriction even on transfers with a >> payload of a multiple of 8 bytes. >=20 > Do you have a reference to this 8 byte alignment requirement? I > couldn't find it browsing through the standard. SBP-2 clause 5.2. It's also in SBP-3 even though there is no obvious benefit for this rule. > Also, since the SBP-2 > driver has to convert the scatterlist to an SBP-2 page table, it can > just allocate the page table on a 8-byte boundary if that is required= =2E Yes, after the discussion this occurred to me too but my energy reserve= s were already too low to wrap this up. > The entries in the scatter table have no alignment restrictions from > the SBP-2 side. >=20 > By the way, is there a way to ask the SCSI stack to limit the size of > the entries in the scatterlist to 64k? This would greatly simplify > the conversion to SBP-2 page tables, since this is the maximum size > these can hold. Douglas has a very informative text on this: http://sg.torque.net/sg/sg_io.html#mozTocId154063 | [...] since lk 2.6.16 another limit comes into play: the | MAX_SEGMENT_SIZE define which is set to 64 KB. MAX_SEGMENT_SIZE is a | default and can be overridden by the LLD calling | blk_queue_max_segment_size(). Looks like we can yank out some cruft off sbp2. --=20 Stefan Richter -=3D=3D=3D=3D=3D-=3D-=3D=3D=3D ---=3D -=3D=3D=3D=3D http://arcgraph.de/sr/ - 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