basic domain validation patches- 3rd and final call

[Scott Long]

Go for it!

Matthew Jacob wrote:
> Please review, or these will be going in as the basis for ongoing
> work. They aren't perfect, but I believe that they are a sorely needed
> start. Speak now or forever hold your piece.
> 
> On 11/2/06, mjacob at freebsd.org <mjacob at freebsd.org> wrote:
>>
>> See http://people.freebsd.org/~mjacob/DV_PATCHES
>>
>> The ANSI document on Domain Validation gives an algorithm for doing
>> Basic Domain Validation as, in part:
>>
>>   Send an INQUIRY command to a SCSI device 3 times- twice with the
>>   default transfer agreement and once with the transfer agreement set
>>   to the fastest supported values. The Basic test fails when the first
>>   36 bytes of data returned at the negotiated synchronous speed does not
>>   match the data received at the asynchronous transfer speed. In
>>   addition, the Basic test fails if a CRC error (or parity error for
>>   non-DT clocking) or a timeout occurs. If data miscompare occurs, the
>>   test should be repeated (e.g., this could be due to the target changing
>>   INQUIRY data during SCSI device initialization). After a finite number
>>   of retries, if data miscompare recurs then fall-back should be
>>   attempted (see 5.5.2).
>>
>> and 5.5.2 has:
>>
>>   If Basic or Enhanced tests fail, a fall-back setting is set and the
>>   tests are performed again. The recommended fall-back order is:
>>
>>      1. fast-160
>>      2. fast-80
>>      3. fast-40 (with DT clocking enabled)
>>      4. fast-40 (with ST clocking enabled)
>>      5. fast-20
>>      6. fast-10; and
>>      7. asynchrnous transfer.
>>
>> I've done an implementation interwoven into the probe code in cam_xpt
>> such that the following occurs..
>>
>> The normal sequence is:
>>
>>      ...
>>      INQUIRY (short)
>>      INQUIRY (long)
>>      ...
>>      ('default' sync settings are enabled)
>>      ...
>>      PROBE_TUR_FOR_NEGOTIATION
>>      <END>
>>
>> I've changed <END> to be:
>>
>>      PROBE_TUR_FOR_NEGOTIATION
>>      PROBE_INQUIRY_BASIC_DV1
>>      ...
>>      PROBE_INQUIRY_BASIC_DV2
>>      ...
>>
>> The idea here is to leverage the two initial INQUIRY commands done at
>> async mode and compare with the last known one and to do *two*
>> additional INQUIRY commands (at speed) to see if they compare with the
>> last ASYNC long INQUIRY command. If they don't, we can do backoff and
>> just re-enter the state machine at PROBE_TUR_FOR_NEGOTIATION.
>>
>> The backoff doesn't do DT/ST settings, but just simply increments the
>> sync_period factor until we hit 0xf (5 MHz) and then drops to async.
>>
>> I don't mess with PPR settings on the theory that the SIM will do the
>> right thing with PPR settings depending on the values of sync period and
>> offset.
>>
>> By doing fault injection (e..g, failed compares) I've done some testing
>> and this *appears* to do what one would want.
>>
>> Any comments? I *know* there are people out there on this list who have
>> more experience with DV than I do so I'd appreciate some comments.
>>
>> -matt
>>
>>
>>
>>
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