Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755607Ab2BGKHZ (ORCPT ); Tue, 7 Feb 2012 05:07:25 -0500 Received: from mail-iy0-f174.google.com ([209.85.210.174]:37682 "EHLO mail-iy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754284Ab2BGKHV convert rfc822-to-8bit (ORCPT ); Tue, 7 Feb 2012 05:07:21 -0500 MIME-Version: 1.0 In-Reply-To: <4F30D4F6.1040802@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> <476E7976-738A-4202-9FC4-FA5B060EA95F@bootc.net> <4F30D4F6.1040802@bootc.net> From: Julian Calaby Date: Tue, 7 Feb 2012 21:06:57 +1100 Message-ID: Subject: Re: FireWire/SBP2 Target mode To: Chris Boot 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-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4402 Lines: 113 Hi, On Tue, Feb 7, 2012 at 18:38, Chris Boot wrote: > On 06/02/2012 23:09, Chris Boot wrote: >> >> >> 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. > > > Hmm sorry I've thought about this overnight and clearly I was talking > rubbish. Yes, I need to reply in the fw_address_handler but all I tend to do > in there is schedule a task to the the main part of the work anyway. As most > of the operations require fetching an ORB from the initiator I have to do > this from user context. > > So it's possible I could do this by waiting in my scheduled work function > until the fw_node is available and get the speed from that - but that seems > like an inordinate amount of work when I can follow the standard and do it > really easily by pulling it out of the fw_request. Fair enough, I assumed that there might have been some reason why you wouldn't have it at that point, not just convention getting in the way. Thanks, -- Julian Calaby Email: julian.calaby@gmail.com Profile: http://www.google.com/profiles/julian.calaby/ .Plan: http://sites.google.com/site/juliancalaby/ -- 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/