From mboxrd@z Thu Jan 1 00:00:00 1970 From: Chris Boot Subject: Re: FireWire/SBP2 Target mode Date: Tue, 07 Feb 2012 07:38:30 +0000 Message-ID: <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> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <476E7976-738A-4202-9FC4-FA5B060EA95F@bootc.net> Sender: target-devel-owner@vger.kernel.org To: Julian Calaby 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 List-Id: linux-scsi@vger.kernel.org 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_AGE= NT >>>>> register is received shall determine the speed used by the target= for >>>>> all subsequent requests to read the initiator=E2=80=99s configura= tion ROM, fetch >>>>> ORB=E2=80=99s from initiator memory or store status at the initia= tor=E2=80=99s >>>>> status_FIFO. Command block ORB=E2=80=99s separately specify the s= peed 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 le= tter >>>> 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 implemen= tations >>>> that do not need to implement topology scanning. I have a hard ti= me to >>>> think of a valid scenario where an initiator needs to be able to s= teer a >>>> target towards a lower wire speed than what the participating link= s 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 acc= ess 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= =2E I'd have to turn away the requester and hope they try again. I'm fa= irly 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 t= he >> 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 sc= heduled something on a work queue. Please correct me if I'm wrong thoug= h, as that might be useful anyway. Hmm sorry I've thought about this overnight and clearly I was talking=20 rubbish. Yes, I need to reply in the fw_address_handler but all I tend=20 to do in there is schedule a task to the the main part of the work=20 anyway. As most of the operations require fetching an ORB from the=20 initiator I have to do this from user context. So it's possible I could do this by waiting in my scheduled work=20 function until the fw_node is available and get the speed from that -=20 but that seems like an inordinate amount of work when I can follow the=20 standard and do it really easily by pulling it out of the fw_request. Chris --=20 Chris Boot bootc@bootc.net Tel: 01271 414100