I don't see any problem removing the
hard_reset wording from the PL_PM state machine. But I see no harm in leaving
it there either. If it is removed then it should be completely removed
because if PL_PM is in the idle state then there are no operations to terminate.
Of course all this assumes you are correct
in your assumption that a Phy Disabled confirmation always comes before
a Hard_Reset. I admit I did not dig down to that level.
The problem is that
the text specifying "operations are terminated" is described
in transitions from PL_PM2 or PL_PM3 to PL_PM1:IDLE, and are associated
with a condition that will never occur in those states (i.e., HARD RESET
Received confirmation). That's because of the constraint that a HARD RESET
primitive cannot be recognized until after DWS is lost COMINITs and COMSAS
have been exchanged, and speed negotiation has completed - long after the
PL_PM state machine made it's transition to PL_PM1. So, at a minimum, we
have state transition trigger conditions defined that are meaningless since
the PL_PM will never be in the PL_PM2 or PL_PM3 state when the HARD RESET
primitive is recognized. Because the text about "all operations are
terminated" is associated with state transition conditions that will
never occur, I'm concerned that if the state machine is implemented scritly
according to the text, the operations will not be terminated when they
need to.
Wouldn't it make more
sense to remove the transition conditions related to the HARD RESET Received
confirmation defined for the PL_PM2 and PL_PM3 states, and instead put
a statement in the PL_PM1:IDLE state general description along the lines
of:
If
a HARD RESET Received confirmation is received in this state, all operations
are terminated.
?
Bob
From: George Penokie [mailto:gop@us.ibm.com]
Sent: Friday, March 02, 2007 8:21 AM
To: Sheffield, Robert L
Cc: owner-t10@t10.org; T10 Reflector
Subject: Re: SAS-2: HARD RESET stalls at PL_PM
Bob,
Don't know if anyone responded to this. But here's my 2 cents.
I don't see any problem. The hard_reset goes to the PL_OC and those states
forward it up to the transport layer. The information in the PL_PM is only
there to get PL_PM back to idle. Remember, that the port layer is not just
the PL_PM but also includes the PL_OC. So there is no stalling of the hard_reset
at PL.
"Sheffield, Robert
L" <robert.l.sheffield@intel.com>
Sent by: owner-t10@t10.org
02/08/2007 02:09 PM
To
"T10 Reflector"
<t10@t10.org>
cc
Subject
SAS-2: HARD RESET stalls at PL_PM
One of our designers noticed an interesting conundrum in looking at the
details of the PL_PM state machine and how a HARD RESET arriving on the
wire is processed. It appears the intent is to "terminate all operations",
however when walking through the specific state sequences, this doesn't
appear to happen in most cases (except when there's an outstanding OPEN
address frame).
There are two other places where the PL_PM processing of a HARD_RESET Received
confirmation is specified:
8.2.3.3.6 Transition PL_PM2:Req_Wait to PL_PM1:Idle
This transition shall occur after:
a) a Retry Open message is sent to the PL_OC state machine;
b) an Unable To Connect message is sent to the PL_OC state machine;
c) all operations have been terminated after a HARD_RESET Received confirmation
is received; or
d) a Phy Disabled confirmation is received.
8.2.3.4.2 Transition PL_PM3:Connected to PL_PM1:Idle
This transition shall occur after:
a) a Connection Closed (Transition to Idle) message is sent to the PL_OC
state machine; or
b) all operations are terminated after a HARD_RESET Received confirmation
is received.
The trouble is, the PL_PM will never be in the PL_PM2 or PL_PM3 state when
the HARD_RESET Received confirmation is received. The PL_PM2 state machine
will take the transition to PL_PM1 based on condition (d) first, and the
PL_PM3 state will take the transition to PL_PM1 based on condition (a)
first.
The SP state machine takes a transition to SP0:OOB_COMINIT upon receiving
COMINIT/DWS Lost.
The SP0:OOB_COMINIT state sends a Phy Layer Not Ready confirmation to the
link layer.
Receiving a Phy Layer Not Ready confirmation causes the SL_IR_IRC state
machine to transition to the SL_IR_IRC1:Idle state.
The SL_IR_IRC1:Idle state sends a Phy Disabled confirmation to the port
layer, and an Enable Disable SAS Link (Disable) message to the SL state
machines.
Receiving a Phy Disabled confirmation (condition d) causes the transition
PL_PM2->PL_PM1.
Receiving an Enable Disable SAS Link (Disable) message causes the SL_CC
state machine to transition to SL_CC0:Idle.
The SL_CC0:Idle state sends a Connection Closed (Transition to Idle) confirmation
to the port layer
Receiving a Connection Closed (Transition to Idle) confirmation
(condition a) causes the transition PL_PM3->PL_PM1.
All of this happens before the HARD RESET part of the link reset sequence
can occur, and so the PL_PM state machine is in PL_PM1:Idle when the HARD
RESET Received confirmation is processed. PL_PM1:Idle specifies no processing
based on the HARD_RESET Received confirmation.
Perhaps I'm missing something - is there something that prevents the SP
state machine from transmitting Phy Layer Not Ready at the beginning of
a link reset sequence?