Documentation/scsi/libsas.txt

   1 SAS Layer
   2 ---------
   3
   4 The SAS Layer is a management infrastructure which manages
   5 SAS LLDDs.  It sits between SCSI Core and SAS LLDDs.  The
   6 layout is as follows: while SCSI Core is concerned with
   7 SAM/SPC issues, and a SAS LLDD+sequencer is concerned with
   8 phy/OOB/link management, the SAS layer is concerned with:
   9
  10       * SAS Phy/Port/HA event management (LLDD generates,
  11         SAS Layer processes),
  12       * SAS Port management (creation/destruction),
  13       * SAS Domain discovery and revalidation,
  14       * SAS Domain device management,
  15       * SCSI Host registration/unregistration,
  16       * Device registration with SCSI Core (SAS) or libata
  17         (SATA), and
  18       * Expander management and exporting expander control
  19         to user space.
  20
  21 A SAS LLDD is a PCI device driver.  It is concerned with
  22 phy/OOB management, and vendor specific tasks and generates
  23 events to the SAS layer.
  24
  25 The SAS Layer does most SAS tasks as outlined in the SAS 1.1
  26 spec.
  27
  28 The sas_ha_struct describes the SAS LLDD to the SAS layer.
  29 Most of it is used by the SAS Layer but a few fields need to
  30 be initialized by the LLDDs.
  31
  32 After initializing your hardware, from the probe() function
  33 you call sas_register_ha(). It will register your LLDD with
  34 the SCSI subsystem, creating a SCSI host and it will
  35 register your SAS driver with the sysfs SAS tree it creates.
  36 It will then return.  Then you enable your phys to actually
  37 start OOB (at which point your driver will start calling the
  38 notify_* event callbacks).
  39
  40 Structure descriptions:
  41
  42 struct sas_phy --------------------
  43 Normally this is statically embedded to your driver's
  44 phy structure:
  45         struct my_phy {
  46                blah;
  47                struct sas_phy sas_phy;
  48                bleh;
  49         };
  50 And then all the phys are an array of my_phy in your HA
  51 struct (shown below).
  52
  53 Then as you go along and initialize your phys you also
  54 initialize the sas_phy struct, along with your own
  55 phy structure.
  56
  57 In general, the phys are managed by the LLDD and the ports
  58 are managed by the SAS layer.  So the phys are initialized
  59 and updated by the LLDD and the ports are initialized and
  60 updated by the SAS layer.
  61
  62 There is a scheme where the LLDD can RW certain fields,
  63 and the SAS layer can only read such ones, and vice versa.
  64 The idea is to avoid unnecessary locking.
  65
  66 enabled -- must be set (0/1)
  67 id -- must be set [0,MAX_PHYS)
  68 class, proto, type, role, oob_mode, linkrate -- must be set
  69 oob_mode --  you set this when OOB has finished and then notify
  70 the SAS Layer.
  71
  72 sas_addr -- this normally points to an array holding the sas
  73 address of the phy, possibly somewhere in your my_phy
  74 struct.
  75
  76 attached_sas_addr -- set this when you (LLDD) receive an
  77 IDENTIFY frame or a FIS frame, _before_ notifying the SAS
  78 layer.  The idea is that sometimes the LLDD may want to fake
  79 or provide a different SAS address on that phy/port and this
  80 allows it to do this.  At best you should copy the sas
  81 address from the IDENTIFY frame or maybe generate a SAS
  82 address for SATA directly attached devices.  The Discover
  83 process may later change this.
  84
  85 frame_rcvd -- this is where you copy the IDENTIFY/FIS frame
  86 when you get it; you lock, copy, set frame_rcvd_size and
  87 unlock the lock, and then call the event.  It is a pointer
  88 since there's no way to know your hw frame size _exactly_,
  89 so you define the actual array in your phy struct and let
  90 this pointer point to it.  You copy the frame from your
  91 DMAable memory to that area holding the lock.
  92
  93 sas_prim -- this is where primitives go when they're
  94 received.  See sas.h. Grab the lock, set the primitive,
  95 release the lock, notify.
  96
  97 port -- this points to the sas_port if the phy belongs
  98 to a port -- the LLDD only reads this. It points to the
  99 sas_port this phy is part of.  Set by the SAS Layer.
 100
 101 ha -- may be set; the SAS layer sets it anyway.
 102
 103 lldd_phy -- you should set this to point to your phy so you
 104 can find your way around faster when the SAS layer calls one
 105 of your callbacks and passes you a phy.  If the sas_phy is
 106 embedded you can also use container_of -- whatever you
 107 prefer.
 108
 109
 110 struct sas_port --------------------
 111 The LLDD doesn't set any fields of this struct -- it only
 112 reads them.  They should be self explanatory.
 113
 114 phy_mask is 32 bit, this should be enough for now, as I
 115 haven't heard of a HA having more than 8 phys.
 116
 117 lldd_port -- I haven't found use for that -- maybe other
 118 LLDD who wish to have internal port representation can make
 119 use of this.
 120
 121
 122 struct sas_ha_struct --------------------
 123 It normally is statically declared in your own LLDD
 124 structure describing your adapter:
 125 struct my_sas_ha {
 126        blah;
 127        struct sas_ha_struct sas_ha;
 128        struct my_phy phys[MAX_PHYS];
 129        struct sas_port sas_ports[MAX_PHYS]; /* (1) */
 130        bleh;
 131 };
 132
 133 (1) If your LLDD doesn't have its own port representation.
 134
 135 What needs to be initialized (sample function given below).
 136
 137 pcidev
 138 sas_addr -- since the SAS layer doesn't want to mess with
 139          memory allocation, etc, this points to statically
 140          allocated array somewhere (say in your host adapter
 141          structure) and holds the SAS address of the host
 142          adapter as given by you or the manufacturer, etc.
 143 sas_port
 144 sas_phy -- an array of pointers to structures. (see
 145         note above on sas_addr).
 146         These must be set.  See more notes below.
 147 num_phys -- the number of phys present in the sas_phy array,
 148          and the number of ports present in the sas_port
 149          array.  There can be a maximum num_phys ports (one per
 150          port) so we drop the num_ports, and only use
 151          num_phys.
 152
 153 The event interface:
 154
 155         /* LLDD calls these to notify the class of an event. */
 156         void (*notify_ha_event)(struct sas_ha_struct *, enum ha_event);
 157         void (*notify_port_event)(struct sas_phy *, enum port_event);
 158         void (*notify_phy_event)(struct sas_phy *, enum phy_event);
 159
 160 When sas_register_ha() returns, those are set and can be
 161 called by the LLDD to notify the SAS layer of such events
 162 the SAS layer.
 163
 164 The port notification:
 165
 166         /* The class calls these to notify the LLDD of an event. */
 167         void (*lldd_port_formed)(struct sas_phy *);
 168         void (*lldd_port_deformed)(struct sas_phy *);
 169
 170 If the LLDD wants notification when a port has been formed
 171 or deformed it sets those to a function satisfying the type.
 172
 173 A SAS LLDD should also implement at least one of the Task
 174 Management Functions (TMFs) described in SAM:
 175
 176         /* Task Management Functions. Must be called from process context. */
 177         int (*lldd_abort_task)(struct sas_task *);
 178         int (*lldd_abort_task_set)(struct domain_device *, u8 *lun);
 179         int (*lldd_clear_aca)(struct domain_device *, u8 *lun);
 180         int (*lldd_clear_task_set)(struct domain_device *, u8 *lun);
 181         int (*lldd_I_T_nexus_reset)(struct domain_device *);
 182         int (*lldd_lu_reset)(struct domain_device *, u8 *lun);
 183         int (*lldd_query_task)(struct sas_task *);
 184
 185 For more information please read SAM from T10.org.
 186
 187 Port and Adapter management:
 188
 189         /* Port and Adapter management */
 190         int (*lldd_clear_nexus_port)(struct sas_port *);
 191         int (*lldd_clear_nexus_ha)(struct sas_ha_struct *);
 192
 193 A SAS LLDD should implement at least one of those.
 194
 195 Phy management:
 196
 197         /* Phy management */
 198         int (*lldd_control_phy)(struct sas_phy *, enum phy_func);
 199
 200 lldd_ha -- set this to point to your HA struct. You can also
 201 use container_of if you embedded it as shown above.
 202
 203 A sample initialization and registration function
 204 can look like this (called last thing from probe())
 205 *but* before you enable the phys to do OOB:
 206
 207 static int register_sas_ha(struct my_sas_ha *my_ha)
 208 {
 209         int i;
 210         static struct sas_phy   *sas_phys[MAX_PHYS];
 211         static struct sas_port  *sas_ports[MAX_PHYS];
 212
 213         my_ha->sas_ha.sas_addr = &my_ha->sas_addr[0];
 214
 215         for (i = 0; i < MAX_PHYS; i++) {
 216                 sas_phys[i] = &my_ha->phys[i].sas_phy;
 217                 sas_ports[i] = &my_ha->sas_ports[i];
 218         }
 219
 220         my_ha->sas_ha.sas_phy  = sas_phys;
 221         my_ha->sas_ha.sas_port = sas_ports;
 222         my_ha->sas_ha.num_phys = MAX_PHYS;
 223
 224         my_ha->sas_ha.lldd_port_formed = my_port_formed;
 225
 226         my_ha->sas_ha.lldd_dev_found = my_dev_found;
 227         my_ha->sas_ha.lldd_dev_gone = my_dev_gone;
 228
 229         my_ha->sas_ha.lldd_max_execute_num = lldd_max_execute_num; (1)
 230
 231         my_ha->sas_ha.lldd_queue_size = ha_can_queue;
 232         my_ha->sas_ha.lldd_execute_task = my_execute_task;
 233
 234         my_ha->sas_ha.lldd_abort_task     = my_abort_task;
 235         my_ha->sas_ha.lldd_abort_task_set = my_abort_task_set;
 236         my_ha->sas_ha.lldd_clear_aca      = my_clear_aca;
 237         my_ha->sas_ha.lldd_clear_task_set = my_clear_task_set;
 238         my_ha->sas_ha.lldd_I_T_nexus_reset= NULL; (2)
 239         my_ha->sas_ha.lldd_lu_reset       = my_lu_reset;
 240         my_ha->sas_ha.lldd_query_task     = my_query_task;
 241
 242         my_ha->sas_ha.lldd_clear_nexus_port = my_clear_nexus_port;
 243         my_ha->sas_ha.lldd_clear_nexus_ha = my_clear_nexus_ha;
 244
 245         my_ha->sas_ha.lldd_control_phy = my_control_phy;
 246
 247         return sas_register_ha(&my_ha->sas_ha);
 248 }
 249
 250 (1) This is normally a LLDD parameter, something of the
 251 lines of a task collector.  What it tells the SAS Layer is
 252 whether the SAS layer should run in Direct Mode (default:
 253 value 0 or 1) or Task Collector Mode (value greater than 1).
 254
 255 In Direct Mode, the SAS Layer calls Execute Task as soon as
 256 it has a command to send to the SDS, _and_ this is a single
 257 command, i.e. not linked.
 258
 259 Some hardware (e.g. aic94xx) has the capability to DMA more
 260 than one task at a time (interrupt) from host memory.  Task
 261 Collector Mode is an optional feature for HAs which support
 262 this in their hardware.  (Again, it is completely optional
 263 even if your hardware supports it.)
 264
 265 In Task Collector Mode, the SAS Layer would do _natural_
 266 coalescing of tasks and at the appropriate moment it would
 267 call your driver to DMA more than one task in a single HA
 268 interrupt. DMBS may want to use this by insmod/modprobe
 269 setting the lldd_max_execute_num to something greater than
 270 1.
 271
 272 (2) SAS 1.1 does not define I_T Nexus Reset TMF.
 273
 274 Events
 275 ------
 276
 277 Events are _the only way_ a SAS LLDD notifies the SAS layer
 278 of anything.  There is no other method or way a LLDD to tell
 279 the SAS layer of anything happening internally or in the SAS
 280 domain.
 281
 282 Phy events:
 283         PHYE_LOSS_OF_SIGNAL, (C)
 284         PHYE_OOB_DONE,
 285         PHYE_OOB_ERROR,      (C)
 286         PHYE_SPINUP_HOLD.
 287
 288 Port events, passed on a _phy_:
 289         PORTE_BYTES_DMAED,      (M)
 290         PORTE_BROADCAST_RCVD,   (E)
 291         PORTE_LINK_RESET_ERR,   (C)
 292         PORTE_TIMER_EVENT,      (C)
 293         PORTE_HARD_RESET.
 294
 295 Host Adapter event:
 296         HAE_RESET
 297
 298 A SAS LLDD should be able to generate
 299         - at least one event from group C (choice),
 300         - events marked M (mandatory) are mandatory (only one),
 301         - events marked E (expander) if it wants the SAS layer
 302           to handle domain revalidation (only one such).
 303         - Unmarked events are optional.
 304
 305 Meaning:
 306
 307 HAE_RESET -- when your HA got internal error and was reset.
 308
 309 PORTE_BYTES_DMAED -- on receiving an IDENTIFY/FIS frame
 310 PORTE_BROADCAST_RCVD -- on receiving a primitive
 311 PORTE_LINK_RESET_ERR -- timer expired, loss of signal, loss
 312 of DWS, etc. (*)
 313 PORTE_TIMER_EVENT -- DWS reset timeout timer expired (*)
 314 PORTE_HARD_RESET -- Hard Reset primitive received.
 315
 316 PHYE_LOSS_OF_SIGNAL -- the device is gone (*)
 317 PHYE_OOB_DONE -- OOB went fine and oob_mode is valid
 318 PHYE_OOB_ERROR -- Error while doing OOB, the device probably
 319 got disconnected. (*)
 320 PHYE_SPINUP_HOLD -- SATA is present, COMWAKE not sent.
 321
 322 (*) should set/clear the appropriate fields in the phy,
 323     or alternatively call the inlined sas_phy_disconnected()
 324     which is just a helper, from their tasklet.
 325
 326 The Execute Command SCSI RPC:
 327
 328         int (*lldd_execute_task)(struct sas_task *, int num,
 329                                  unsigned long gfp_flags);
 330
 331 Used to queue a task to the SAS LLDD.  @task is the tasks to
 332 be executed.  @num should be the number of tasks being
 333 queued at this function call (they are linked listed via
 334 task::list), @gfp_mask should be the gfp_mask defining the
 335 context of the caller.
 336
 337 This function should implement the Execute Command SCSI RPC,
 338 or if you're sending a SCSI Task as linked commands, you
 339 should also use this function.
 340
 341 That is, when lldd_execute_task() is called, the command(s)
 342 go out on the transport *immediately*.  There is *no*
 343 queuing of any sort and at any level in a SAS LLDD.
 344
 345 The use of task::list is two-fold, one for linked commands,
 346 the other discussed below.
 347
 348 It is possible to queue up more than one task at a time, by
 349 initializing the list element of struct sas_task, and
 350 passing the number of tasks enlisted in this manner in num.
 351
 352 Returns: -SAS_QUEUE_FULL, -ENOMEM, nothing was queued;
 353          0, the task(s) were queued.
 354
 355 If you want to pass num > 1, then either
 356 A) you're the only caller of this function and keep track
 357    of what you've queued to the LLDD, or
 358 B) you know what you're doing and have a strategy of
 359    retrying.
 360
 361 As opposed to queuing one task at a time (function call),
 362 batch queuing of tasks, by having num > 1, greatly
 363 simplifies LLDD code, sequencer code, and _hardware design_,
 364 and has some performance advantages in certain situations
 365 (DBMS).
 366
 367 The LLDD advertises if it can take more than one command at
 368 a time at lldd_execute_task(), by setting the
 369 lldd_max_execute_num parameter (controlled by "collector"
 370 module parameter in aic94xx SAS LLDD).
 371
 372 You should leave this to the default 1, unless you know what
 373 you're doing.
 374
 375 This is a function of the LLDD, to which the SAS layer can
 376 cater to.
 377
 378 int lldd_queue_size
 379         The host adapter's queue size.  This is the maximum
 380 number of commands the lldd can have pending to domain
 381 devices on behalf of all upper layers submitting through
 382 lldd_execute_task().
 383
 384 You really want to set this to something (much) larger than
 385 1.
 386
 387 This _really_ has absolutely nothing to do with queuing.
 388 There is no queuing in SAS LLDDs.
 389
 390 struct sas_task {
 391         dev -- the device this task is destined to
 392         list -- must be initialized (INIT_LIST_HEAD)
 393         task_proto -- _one_ of enum sas_proto
 394         scatter -- pointer to scatter gather list array
 395         num_scatter -- number of elements in scatter
 396         total_xfer_len -- total number of bytes expected to be transferred
 397         data_dir -- PCI_DMA_...
 398         task_done -- callback when the task has finished execution
 399 };
 400
 401 DISCOVERY
 402 ---------
 403
 404 The sysfs tree has the following purposes:
 405     a) It shows you the physical layout of the SAS domain at
 406        the current time, i.e. how the domain looks in the
 407        physical world right now.
 408     b) Shows some device parameters _at_discovery_time_.
 409
 410 This is a link to the tree(1) program, very useful in
 411 viewing the SAS domain:
 412 ftp://mama.indstate.edu/linux/tree/
 413 I expect user space applications to actually create a
 414 graphical interface of this.
 415
 416 That is, the sysfs domain tree doesn't show or keep state if
 417 you e.g., change the meaning of the READY LED MEANING
 418 setting, but it does show you the current connection status
 419 of the domain device.
 420
 421 Keeping internal device state changes is responsibility of
 422 upper layers (Command set drivers) and user space.
 423
 424 When a device or devices are unplugged from the domain, this
 425 is reflected in the sysfs tree immediately, and the device(s)
 426 removed from the system.
 427
 428 The structure domain_device describes any device in the SAS
 429 domain.  It is completely managed by the SAS layer.  A task
 430 points to a domain device, this is how the SAS LLDD knows
 431 where to send the task(s) to.  A SAS LLDD only reads the
 432 contents of the domain_device structure, but it never creates
 433 or destroys one.
 434
 435 Expander management from User Space
 436 -----------------------------------
 437
 438 In each expander directory in sysfs, there is a file called
 439 "smp_portal".  It is a binary sysfs attribute file, which
 440 implements an SMP portal (Note: this is *NOT* an SMP port),
 441 to which user space applications can send SMP requests and
 442 receive SMP responses.
 443
 444 Functionality is deceptively simple:
 445
 446 1. Build the SMP frame you want to send. The format and layout
 447    is described in the SAS spec.  Leave the CRC field equal 0.
 448 open(2)
 449 2. Open the expander's SMP portal sysfs file in RW mode.
 450 write(2)
 451 3. Write the frame you built in 1.
 452 read(2)
 453 4. Read the amount of data you expect to receive for the frame you built.
 454    If you receive different amount of data you expected to receive,
 455    then there was some kind of error.
 456 close(2)
 457 All this process is shown in detail in the function do_smp_func()
 458 and its callers, in the file "expander_conf.c".
 459
 460 The kernel functionality is implemented in the file
 461 "sas_expander.c".
 462
 463 The program "expander_conf.c" implements this. It takes one
 464 argument, the sysfs file name of the SMP portal to the
 465 expander, and gives expander information, including routing
 466 tables.
 467
 468 The SMP portal gives you complete control of the expander,
 469 so please be careful.