Messages in this thread |  | | | Date | Tue, 07 Feb 2012 07:38:30 +0000 | | From | Chris Boot <> | | Subject | Re: FireWire/SBP2 Target mode |
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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<bootc@bootc.net> 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.
Chris
-- Chris Boot bootc@bootc.net Tel: 01271 414100 -- 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/
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