Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756223Ab2BFXJz (ORCPT ); Mon, 6 Feb 2012 18:09:55 -0500 Received: from kamaji.grokhost.net ([87.117.218.43]:60152 "EHLO kamaji.grokhost.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756029Ab2BFXJx convert rfc822-to-8bit (ORCPT ); Mon, 6 Feb 2012 18:09:53 -0500 Subject: Re: FireWire/SBP2 Target mode Mime-Version: 1.0 (Apple Message framework v1257) Content-Type: text/plain; charset=windows-1252 From: Chris Boot In-Reply-To: Date: Mon, 6 Feb 2012 23:09:49 +0000 Cc: Stefan Richter , Clemens Ladisch , target-devel@vger.kernel.org, linux1394-devel@lists.sourceforge.net, Boaz Harrosh , Andy Grover , linux-scsi@vger.kernel.org, lkml Content-Transfer-Encoding: 8BIT Message-Id: <476E7976-738A-4202-9FC4-FA5B060EA95F@bootc.net> References: <4E4BD560.4010806@bootc.net> <4E4D3B88.30003@ladisch.de> <4F29978A.3010707@redhat.com> <20120201224156.0773ebc6@stein> <4F2A55B9.4040005@panasas.com> <4F2A60DC.9030007@ladisch.de> <4F2FD1F4.9050702@bootc.net> <4F2FE705.3070509@ladisch.de> <4F2FE8DA.70502@bootc.net> <20120206212628.6880c506@stein> <5C167A1D-2203-4F1C-B538-E99DD87E7E42@bootc.net> To: Julian Calaby X-Mailer: Apple Mail (2.1257) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3150 Lines: 63 On 6 Feb 2012, at 23:00, Julian Calaby wrote: > Hi, > > On Tue, Feb 7, 2012 at 09:28, Chris Boot wrote: >> On 6 Feb 2012, at 20:26, Stefan Richter wrote: >> >>> On Feb 06 Chris Boot wrote: >>>> On 06/02/2012 14:43, Clemens Ladisch wrote: >>>>> Chris Boot wrote: >>>>>> You can pull the code from: >>>>>> git://github.com/bootc/Linux-SBP-2-Target.git >>>>> >>>>> The TODO file says: >>>>>> * Update Juju so we can get the speed in the fw_address_handler callback >>>>> >>>>> What is the speed needed for? >>>> >>>> "The speed at which the block write request to the MANAGEMENT_AGENT >>>> register is received shall determine the speed used by the target for >>>> all subsequent requests to read the initiator?s configuration ROM, fetch >>>> ORB?s from initiator memory or store status at the initiator?s >>>> status_FIFO. Command block ORB?s separately specify the speed for >>>> requests addressed to the data buffer or page table." >>>> >>>> (T10/1155D Revision 4 page 53/54) >>> >>> I guess it is not too hard to add this to the AR-req handler. On the >>> other hand, I see little reason to follow the SBP-2 spec to the letter >>> here. The target driver could just use the maximum speed that the core >>> figured out. On the other hand, this requires of course >>> - the target to wait for core to finish scanning an initiator, >>> - the core to offer an API to look up an fw_device by a >>> card--generation--nodeID tuple. >>> >>> The intention of the spec is IMO clearly to enable target implementations >>> that do not need to implement topology scanning. I have a hard time to >>> think of a valid scenario where an initiator needs to be able to steer a >>> target towards a lower wire speed than what the participating links and >>> PHYs actually support. >> >> The only thing stopping me from getting the speed is the fact that struct fw_request is opaque. The value is easily available from request->response.speed and I kind of do that already in a very hackish way. I've sent a separate patch which adds a function that can be used to access that one value. >> >> Waiting until the bus scan is complete isn't actually that great as I see the first LOGIN requests often before the fw_node is seen at all. I'd have to turn away the requester and hope they try again. I'm fairly sure my little tweak in my patch is a simple enough solution. > > Stupid question: Could you use a completion queue or something > equivalent to wait until you have seen the fw_node, *then* process the > LOGIN request? The fw_address_handler callback is called in interrupt context, and I can't sleep from within there. As far as I'm aware I must call fw_send_response() from within the callback and can't defer that until I've scheduled something on a work queue. Please correct me if I'm wrong though, as that might be useful anyway. Chris -- Chris Boot bootc@bootc.net -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/