linux_dsm_epyc7002/Documentation/scsi/libsas.txt

SAS Layer
---------

The SAS Layer is a management infrastructure which manages
SAS LLDDs.  It sits between SCSI Core and SAS LLDDs.  The
layout is as follows: while SCSI Core is concerned with
SAM/SPC issues, and a SAS LLDD+sequencer is concerned with
phy/OOB/link management, the SAS layer is concerned with:

      * SAS Phy/Port/HA event management (LLDD generates,
        SAS Layer processes),
      * SAS Port management (creation/destruction),
      * SAS Domain discovery and revalidation,
      * SAS Domain device management,
      * SCSI Host registration/unregistration,
      * Device registration with SCSI Core (SAS) or libata
        (SATA), and
      * Expander management and exporting expander control
        to user space.

A SAS LLDD is a PCI device driver.  It is concerned with
phy/OOB management, and vendor specific tasks and generates
events to the SAS layer.

The SAS Layer does most SAS tasks as outlined in the SAS 1.1
spec.

The sas_ha_struct describes the SAS LLDD to the SAS layer.
Most of it is used by the SAS Layer but a few fields need to
be initialized by the LLDDs.

After initializing your hardware, from the probe() function
you call sas_register_ha(). It will register your LLDD with
the SCSI subsystem, creating a SCSI host and it will
register your SAS driver with the sysfs SAS tree it creates.
It will then return.  Then you enable your phys to actually
start OOB (at which point your driver will start calling the
notify_* event callbacks).

Structure descriptions:

struct sas_phy --------------------
Normally this is statically embedded to your driver's
phy structure:
	struct my_phy {
	       blah;
	       struct sas_phy sas_phy;
	       bleh;
	};
And then all the phys are an array of my_phy in your HA
struct (shown below).

Then as you go along and initialize your phys you also
initialize the sas_phy struct, along with your own
phy structure.

In general, the phys are managed by the LLDD and the ports
are managed by the SAS layer.  So the phys are initialized
and updated by the LLDD and the ports are initialized and
updated by the SAS layer.

There is a scheme where the LLDD can RW certain fields,
and the SAS layer can only read such ones, and vice versa.
The idea is to avoid unnecessary locking.

enabled -- must be set (0/1)
id -- must be set [0,MAX_PHYS)
class, proto, type, role, oob_mode, linkrate -- must be set
oob_mode --  you set this when OOB has finished and then notify
the SAS Layer.

sas_addr -- this normally points to an array holding the sas
address of the phy, possibly somewhere in your my_phy
struct.

attached_sas_addr -- set this when you (LLDD) receive an
IDENTIFY frame or a FIS frame, _before_ notifying the SAS
layer.  The idea is that sometimes the LLDD may want to fake
or provide a different SAS address on that phy/port and this
allows it to do this.  At best you should copy the sas
address from the IDENTIFY frame or maybe generate a SAS
address for SATA directly attached devices.  The Discover
process may later change this.

frame_rcvd -- this is where you copy the IDENTIFY/FIS frame
when you get it; you lock, copy, set frame_rcvd_size and
unlock the lock, and then call the event.  It is a pointer
since there's no way to know your hw frame size _exactly_,
so you define the actual array in your phy struct and let
this pointer point to it.  You copy the frame from your
DMAable memory to that area holding the lock.

sas_prim -- this is where primitives go when they're
received.  See sas.h. Grab the lock, set the primitive,
release the lock, notify.

port -- this points to the sas_port if the phy belongs
to a port -- the LLDD only reads this. It points to the
sas_port this phy is part of.  Set by the SAS Layer.

ha -- may be set; the SAS layer sets it anyway.

lldd_phy -- you should set this to point to your phy so you
can find your way around faster when the SAS layer calls one
of your callbacks and passes you a phy.  If the sas_phy is
embedded you can also use container_of -- whatever you
prefer.


struct sas_port --------------------
The LLDD doesn't set any fields of this struct -- it only
reads them.  They should be self explanatory.

phy_mask is 32 bit, this should be enough for now, as I
haven't heard of a HA having more than 8 phys.

lldd_port -- I haven't found use for that -- maybe other
LLDD who wish to have internal port representation can make
use of this.


struct sas_ha_struct --------------------
It normally is statically declared in your own LLDD
structure describing your adapter:
struct my_sas_ha {
       blah;
       struct sas_ha_struct sas_ha;
       struct my_phy phys[MAX_PHYS];
       struct sas_port sas_ports[MAX_PHYS]; /* (1) */
       bleh;
};

(1) If your LLDD doesn't have its own port representation.

What needs to be initialized (sample function given below).

pcidev
sas_addr -- since the SAS layer doesn't want to mess with
	 memory allocation, etc, this points to statically
	 allocated array somewhere (say in your host adapter
	 structure) and holds the SAS address of the host
	 adapter as given by you or the manufacturer, etc.
sas_port
sas_phy -- an array of pointers to structures. (see
	note above on sas_addr).
	These must be set.  See more notes below.
num_phys -- the number of phys present in the sas_phy array,
	 and the number of ports present in the sas_port
	 array.  There can be a maximum num_phys ports (one per
	 port) so we drop the num_ports, and only use
	 num_phys.

The event interface:

	/* LLDD calls these to notify the class of an event. */
	void (*notify_ha_event)(struct sas_ha_struct *, enum ha_event);
	void (*notify_port_event)(struct sas_phy *, enum port_event);
	void (*notify_phy_event)(struct sas_phy *, enum phy_event);

When sas_register_ha() returns, those are set and can be
called by the LLDD to notify the SAS layer of such events
the SAS layer.

The port notification:

	/* The class calls these to notify the LLDD of an event. */
	void (*lldd_port_formed)(struct sas_phy *);
	void (*lldd_port_deformed)(struct sas_phy *);

If the LLDD wants notification when a port has been formed
or deformed it sets those to a function satisfying the type.

A SAS LLDD should also implement at least one of the Task
Management Functions (TMFs) described in SAM:

	/* Task Management Functions. Must be called from process context. */
	int (*lldd_abort_task)(struct sas_task *);
	int (*lldd_abort_task_set)(struct domain_device *, u8 *lun);
	int (*lldd_clear_aca)(struct domain_device *, u8 *lun);
	int (*lldd_clear_task_set)(struct domain_device *, u8 *lun);
	int (*lldd_I_T_nexus_reset)(struct domain_device *);
	int (*lldd_lu_reset)(struct domain_device *, u8 *lun);
	int (*lldd_query_task)(struct sas_task *);

For more information please read SAM from T10.org.

Port and Adapter management:

	/* Port and Adapter management */
	int (*lldd_clear_nexus_port)(struct sas_port *);
	int (*lldd_clear_nexus_ha)(struct sas_ha_struct *);

A SAS LLDD should implement at least one of those.

Phy management:

	/* Phy management */
	int (*lldd_control_phy)(struct sas_phy *, enum phy_func);

lldd_ha -- set this to point to your HA struct. You can also
use container_of if you embedded it as shown above.

A sample initialization and registration function
can look like this (called last thing from probe())
*but* before you enable the phys to do OOB:

static int register_sas_ha(struct my_sas_ha *my_ha)
{
	int i;
	static struct sas_phy   *sas_phys[MAX_PHYS];
	static struct sas_port  *sas_ports[MAX_PHYS];

	my_ha->sas_ha.sas_addr = &my_ha->sas_addr[0];

	for (i = 0; i < MAX_PHYS; i++) {
		sas_phys[i] = &my_ha->phys[i].sas_phy;
		sas_ports[i] = &my_ha->sas_ports[i];
	}

	my_ha->sas_ha.sas_phy  = sas_phys;
	my_ha->sas_ha.sas_port = sas_ports;
	my_ha->sas_ha.num_phys = MAX_PHYS;

	my_ha->sas_ha.lldd_port_formed = my_port_formed;

	my_ha->sas_ha.lldd_dev_found = my_dev_found;
	my_ha->sas_ha.lldd_dev_gone = my_dev_gone;

	my_ha->sas_ha.lldd_max_execute_num = lldd_max_execute_num; (1)

	my_ha->sas_ha.lldd_queue_size = ha_can_queue;
	my_ha->sas_ha.lldd_execute_task = my_execute_task;

	my_ha->sas_ha.lldd_abort_task     = my_abort_task;
	my_ha->sas_ha.lldd_abort_task_set = my_abort_task_set;
	my_ha->sas_ha.lldd_clear_aca      = my_clear_aca;
	my_ha->sas_ha.lldd_clear_task_set = my_clear_task_set;
	my_ha->sas_ha.lldd_I_T_nexus_reset= NULL; (2)
	my_ha->sas_ha.lldd_lu_reset       = my_lu_reset;
	my_ha->sas_ha.lldd_query_task     = my_query_task;

	my_ha->sas_ha.lldd_clear_nexus_port = my_clear_nexus_port;
	my_ha->sas_ha.lldd_clear_nexus_ha = my_clear_nexus_ha;

	my_ha->sas_ha.lldd_control_phy = my_control_phy;

	return sas_register_ha(&my_ha->sas_ha);
}

(1) This is normally a LLDD parameter, something of the
lines of a task collector.  What it tells the SAS Layer is
whether the SAS layer should run in Direct Mode (default:
value 0 or 1) or Task Collector Mode (value greater than 1).

In Direct Mode, the SAS Layer calls Execute Task as soon as
it has a command to send to the SDS, _and_ this is a single
command, i.e. not linked.

Some hardware (e.g. aic94xx) has the capability to DMA more
than one task at a time (interrupt) from host memory.  Task
Collector Mode is an optional feature for HAs which support
this in their hardware.  (Again, it is completely optional
even if your hardware supports it.)

In Task Collector Mode, the SAS Layer would do _natural_
coalescing of tasks and at the appropriate moment it would
call your driver to DMA more than one task in a single HA
interrupt. DMBS may want to use this by insmod/modprobe
setting the lldd_max_execute_num to something greater than
1.

(2) SAS 1.1 does not define I_T Nexus Reset TMF.

Events
------

Events are _the only way_ a SAS LLDD notifies the SAS layer
of anything.  There is no other method or way a LLDD to tell
the SAS layer of anything happening internally or in the SAS
domain.

Phy events:
	PHYE_LOSS_OF_SIGNAL, (C)
	PHYE_OOB_DONE,
	PHYE_OOB_ERROR,      (C)
	PHYE_SPINUP_HOLD.

Port events, passed on a _phy_:
	PORTE_BYTES_DMAED,      (M)
	PORTE_BROADCAST_RCVD,   (E)
	PORTE_LINK_RESET_ERR,   (C)
	PORTE_TIMER_EVENT,      (C)
	PORTE_HARD_RESET.

Host Adapter event:
	HAE_RESET

A SAS LLDD should be able to generate
	- at least one event from group C (choice),
	- events marked M (mandatory) are mandatory (only one),
	- events marked E (expander) if it wants the SAS layer
	  to handle domain revalidation (only one such).
	- Unmarked events are optional.

Meaning:

HAE_RESET -- when your HA got internal error and was reset.

PORTE_BYTES_DMAED -- on receiving an IDENTIFY/FIS frame
PORTE_BROADCAST_RCVD -- on receiving a primitive
PORTE_LINK_RESET_ERR -- timer expired, loss of signal, loss
of DWS, etc. (*)
PORTE_TIMER_EVENT -- DWS reset timeout timer expired (*)
PORTE_HARD_RESET -- Hard Reset primitive received.

PHYE_LOSS_OF_SIGNAL -- the device is gone (*)
PHYE_OOB_DONE -- OOB went fine and oob_mode is valid
PHYE_OOB_ERROR -- Error while doing OOB, the device probably
got disconnected. (*)
PHYE_SPINUP_HOLD -- SATA is present, COMWAKE not sent.

(*) should set/clear the appropriate fields in the phy,
    or alternatively call the inlined sas_phy_disconnected()
    which is just a helper, from their tasklet.

The Execute Command SCSI RPC:

	int (*lldd_execute_task)(struct sas_task *, int num,
				 unsigned long gfp_flags);

Used to queue a task to the SAS LLDD.  @task is the tasks to
be executed.  @num should be the number of tasks being
queued at this function call (they are linked listed via
task::list), @gfp_mask should be the gfp_mask defining the
context of the caller.

This function should implement the Execute Command SCSI RPC,
or if you're sending a SCSI Task as linked commands, you
should also use this function.

That is, when lldd_execute_task() is called, the command(s)
go out on the transport *immediately*.  There is *no*
queuing of any sort and at any level in a SAS LLDD.

The use of task::list is two-fold, one for linked commands,
the other discussed below.

It is possible to queue up more than one task at a time, by
initializing the list element of struct sas_task, and
passing the number of tasks enlisted in this manner in num.

Returns: -SAS_QUEUE_FULL, -ENOMEM, nothing was queued;
	 0, the task(s) were queued.

If you want to pass num > 1, then either
A) you're the only caller of this function and keep track
   of what you've queued to the LLDD, or
B) you know what you're doing and have a strategy of
   retrying.

As opposed to queuing one task at a time (function call),
batch queuing of tasks, by having num > 1, greatly
simplifies LLDD code, sequencer code, and _hardware design_,
and has some performance advantages in certain situations
(DBMS).

The LLDD advertises if it can take more than one command at
a time at lldd_execute_task(), by setting the
lldd_max_execute_num parameter (controlled by "collector"
module parameter in aic94xx SAS LLDD).

You should leave this to the default 1, unless you know what
you're doing.

This is a function of the LLDD, to which the SAS layer can
cater to.

int lldd_queue_size
	The host adapter's queue size.  This is the maximum
number of commands the lldd can have pending to domain
devices on behalf of all upper layers submitting through
lldd_execute_task().

You really want to set this to something (much) larger than
1.

This _really_ has absolutely nothing to do with queuing.
There is no queuing in SAS LLDDs.

struct sas_task {
	dev -- the device this task is destined to
	list -- must be initialized (INIT_LIST_HEAD)
	task_proto -- _one_ of enum sas_proto
	scatter -- pointer to scatter gather list array
	num_scatter -- number of elements in scatter
	total_xfer_len -- total number of bytes expected to be transferred
	data_dir -- PCI_DMA_...
	task_done -- callback when the task has finished execution
};

DISCOVERY
---------

The sysfs tree has the following purposes:
    a) It shows you the physical layout of the SAS domain at
       the current time, i.e. how the domain looks in the
       physical world right now.
    b) Shows some device parameters _at_discovery_time_.

This is a link to the tree(1) program, very useful in
viewing the SAS domain:
ftp://mama.indstate.edu/linux/tree/
I expect user space applications to actually create a
graphical interface of this.

That is, the sysfs domain tree doesn't show or keep state if
you e.g., change the meaning of the READY LED MEANING
setting, but it does show you the current connection status
of the domain device.

Keeping internal device state changes is responsibility of
upper layers (Command set drivers) and user space.

When a device or devices are unplugged from the domain, this
is reflected in the sysfs tree immediately, and the device(s)
removed from the system.

The structure domain_device describes any device in the SAS
domain.  It is completely managed by the SAS layer.  A task
points to a domain device, this is how the SAS LLDD knows
where to send the task(s) to.  A SAS LLDD only reads the
contents of the domain_device structure, but it never creates
or destroys one.

Expander management from User Space
-----------------------------------

In each expander directory in sysfs, there is a file called
"smp_portal".  It is a binary sysfs attribute file, which
implements an SMP portal (Note: this is *NOT* an SMP port),
to which user space applications can send SMP requests and
receive SMP responses.

Functionality is deceptively simple:

1. Build the SMP frame you want to send. The format and layout
   is described in the SAS spec.  Leave the CRC field equal 0.
open(2)
2. Open the expander's SMP portal sysfs file in RW mode.
write(2)
3. Write the frame you built in 1.
read(2)
4. Read the amount of data you expect to receive for the frame you built.
   If you receive different amount of data you expected to receive,
   then there was some kind of error.
close(2)
All this process is shown in detail in the function do_smp_func()
and its callers, in the file "expander_conf.c".

The kernel functionality is implemented in the file
"sas_expander.c".

The program "expander_conf.c" implements this. It takes one
argument, the sysfs file name of the SMP portal to the
expander, and gives expander information, including routing
tables.

The SMP portal gives you complete control of the expander,
so please be careful.