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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

};

When an external entity, entity other than the LLDD or the

SAS Layer, wants to work with a struct domain_device, it

_must_ call kobject_get() when getting a handle on the

device and kobject_put() when it is done with the device.

This does two things:

     A) implements proper kfree() for the device;

     B) increments/decrements the kref for all players:

     domain_device

        all domain_device's ... (if past an expander)

            port

                host adapter

                     pci device

                         and up the ladder, etc.

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.