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From: Julian Calaby <julian.calaby@gmail.com>
Date: Tue, 7 Feb 2012 10:00:38 +1100
Message-ID: <CAGRGNgWf0epcam-jpCzMCSqefCKDSm892mw-X49FrcoRO0QYrQ@mail.gmail.com>
Subject: Re: FireWire/SBP2 Target mode
To: Chris Boot <bootc@bootc.net>
Cc: Stefan Richter <stefanr@s5r6.in-berlin.de>,
        Clemens Ladisch <clemens@ladisch.de>, target-devel@vger.kernel.org,
        linux1394-devel@lists.sourceforge.net,
        Boaz Harrosh <bharrosh@panasas.com>, Andy Grover <agrover@redhat.com>,
        linux-scsi@vger.kernel.org, lkml <linux-kernel@vger.kernel.org>
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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?

Thanks,

-- 
Julian Calaby

Email: julian.calaby@gmail.com
Profile: http://www.google.com/profiles/julian.calaby/
.Plan: http://sites.google.com/site/juliancalaby/
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