1.\" Copyright (c) 1996 2.\" Julian Elischer <julian@FreeBSD.org>. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 10.\" 2. Redistributions in binary form must reproduce the above copyright 11.\" notice, this list of conditions and the following disclaimer in the 12.\" documentation and/or other materials provided with the distribution. 13.\" 14.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 15.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 16.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 17.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 18.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 19.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 20.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 21.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 22.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 23.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 24.\" SUCH DAMAGE. 25.\" 26.\" $FreeBSD$ 27.Dd December 20, 2017 28.Dt CAM 4 29.Os 30.Sh NAME 31.Nm CAM 32.Nd Common Access Method Storage subsystem 33.Sh SYNOPSIS 34.Cd "device scbus" 35.Cd "device ada" 36.Cd "device cd" 37.Cd "device ch" 38.Cd "device da" 39.Cd "device pass" 40.Cd "device pt" 41.Cd "device sa" 42.Cd "options CAMDEBUG" 43.Cd "options CAM_DEBUG_BUS=-1" 44.Cd "options CAM_DEBUG_TARGET=-1" 45.Cd "options CAM_DEBUG_LUN=-1" 46.Cd "options CAM_DEBUG_COMPILE=CAM_DEBUG_INFO|CAM_DEBUG_CDB|CAM_DEBUG_PROBE" 47.Cd "options CAM_DEBUG_FLAGS=CAM_DEBUG_INFO|CAM_DEBUG_CDB" 48.Cd "options CAM_MAX_HIGHPOWER=4" 49.Cd "options SCSI_NO_SENSE_STRINGS" 50.Cd "options SCSI_NO_OP_STRINGS" 51.Cd "options SCSI_DELAY=8000" 52.Sh DESCRIPTION 53The 54.Nm 55subsystem provides a uniform and modular system for the implementation 56of drivers to control various 57.Tn SCSI , 58.Tn ATA , 59.Tn NMVe , 60and 61.Tn MMC / SD 62devices, and to utilize different 63.Tn SCSI , 64.Tn ATA , 65.Tn NVMe , 66and 67.Tn MMC / SD 68host adapters through host adapter drivers. 69When the system probes buses, it attaches any devices it finds to the 70appropriate drivers. 71The 72.Xr pass 4 73driver, if it is configured in the kernel, will attach to all devices. 74.Sh KERNEL CONFIGURATION 75There are a number of generic kernel configuration options for the 76.Nm 77subsystem: 78.Bl -tag -width SCSI_NO_SENSE_STRINGS 79.It Dv CAMDEBUG 80This option compiles in all the 81.Nm 82debugging printf code. 83This will not actually 84cause any debugging information to be printed out when included by itself. 85See below for details. 86.It Dv "CAM_MAX_HIGHPOWER=4" 87This sets the maximum allowable number of concurrent "high power" commands. 88A "high power" command is a command that takes more electrical power than 89most to complete. 90An example of this is the 91.Tn SCSI 92START UNIT command. 93Starting a disk often takes significantly more electrical power than normal 94operation. 95This option allows the 96user to specify how many concurrent high power commands may be outstanding 97without overloading the power supply on his computer. 98.It Dv SCSI_NO_SENSE_STRINGS 99This eliminates text descriptions of each 100.Tn SCSI 101Additional Sense Code and Additional Sense Code Qualifier pair. 102Since this 103is a fairly large text database, eliminating it reduces the size of the 104kernel somewhat. 105This is primarily necessary for boot floppies and other 106low disk space or low memory space environments. 107In most cases, though, 108this should be enabled, since it speeds the interpretation of 109.Tn SCSI 110error messages. 111Do not let the "kernel bloat" zealots get to you -- leave 112the sense descriptions in your kernel! 113.It Dv SCSI_NO_OP_STRINGS 114This disables text descriptions of each 115.Tn SCSI 116opcode. 117This option, like the sense string option above, is primarily 118useful for environments like a boot floppy where kernel size is critical. 119Enabling this option for normal use is not recommended, since it slows 120debugging of 121.Tn SCSI 122problems. 123.It Dv SCSI_DELAY=8000 124This is the 125.Tn SCSI 126"bus settle delay." 127In 128.Nm , 129it is specified in 130.Em milliseconds , 131not seconds like the old 132.Tn SCSI 133layer used to do. 134When the kernel boots, it sends a bus reset to each 135.Tn SCSI 136bus to tell each device to reset itself to a default set of transfer 137negotiations and other settings. 138Most 139.Tn SCSI 140devices need some amount of time to recover from a bus reset. 141Newer disks 142may need as little as 100ms, while old, slow devices may need much longer. 143If the 144.Dv SCSI_DELAY 145is not specified, it defaults to 2 seconds. 146The minimum allowable value for 147.Dv SCSI_DELAY 148is "100", or 100ms. 149One special case is that if the 150.Dv SCSI_DELAY 151is set to 0, that will be taken to mean the "lowest possible value." 152In that case, the 153.Dv SCSI_DELAY 154will be reset to 100ms. 155.El 156.Pp 157All devices and buses support dynamic allocation so that 158an upper number of devices and controllers does not need to be configured; 159.Cd "device da" 160will suffice for any number of disk drivers. 161.Pp 162The devices are either 163.Em wired 164so they appear as a particular device unit or 165.Em counted 166so that they appear as the next available unused unit. 167.Pp 168Units are wired down by setting kernel environment hints. 169This is usually done either interactively from the 170.Xr loader 8 , 171or automatically via the 172.Pa /boot/device.hints 173file. 174The basic syntax is: 175.Bd -literal -offset indent 176hint.device.unit.property="value" 177.Ed 178.Pp 179Individual 180.Nm 181bus numbers can be wired down to specific controllers with 182a config line similar to the following: 183.Bd -literal -offset indent 184hint.scbus.0.at="ahd1" 185.Ed 186.Pp 187This assigns 188.Nm 189bus number 0 to the 190.Em ahd1 191driver instance. 192For controllers supporting more than one bus, a particular bus can be assigned 193as follows: 194.Bd -literal -offset indent 195hint.scbus.0.at="ahc1" 196hint.scbus.0.bus="1" 197.Ed 198.Pp 199This assigns 200.Nm 201bus 0 to the bus 1 instance on 202.Em ahc1 . 203Peripheral drivers can be wired to a specific bus, target, and lun as so: 204.Bd -literal -offset indent 205hint.da.0.at="scbus0" 206hint.da.0.target="0" 207hint.da.0.unit="0" 208.Ed 209.Pp 210This assigns 211.Em da0 212to target 0, unit (lun) 0 of scbus 0. 213Omitting the target or unit hints will instruct 214.Nm 215to treat them as wildcards 216and use the first respective counted instances. 217These examples can be combined together to allow a peripheral device to be 218wired to any particular controller, bus, target, and/or unit instance. 219.Pp 220This also works with 221.Xr nvme 4 222drives as well. 223.Bd -literal -offset indent 224hint.nvme.4.at="pci7:0:0" 225hint.scbus.10.at="nvme4" 226hint.nda.10.at="scbus10" 227hint.nda.10.target="1" 228hint.nda.10.unit="12" 229hint.nda.11.at="scbus10" 230hint.nda.11.target="1" 231hint.nda.11.unit="2" 232.Ed 233.Pp 234This assigns the NVMe card living at PCI bus 7 to scbus 10 (in PCIe, 235slot and function are rarely used and usually 0). 236The target for 237.Xr nda 4 238devices is always 1. 239The unit is the namespace identifier from the drive. 240The namespace id 1 is exported as 241.Tn nda10 242and namespace id 2 is exported as 243.Tn nda11 . 244.Pp 245When you have a mixture of wired down and counted devices then the 246counting begins with the first non-wired down unit for a particular 247type. 248That is, if you have a disk wired down as 249.Em "device da1" , 250then the first non-wired disk shall come on line as 251.Em da2 . 252.Sh ADAPTERS 253The system allows common device drivers to work through many different 254types of adapters. 255The adapters take requests from the upper layers and do 256all IO between the 257.Tn SCSI , 258.Tn ATA , 259.Tn NVMe , 260or 261.Tn MMC / SD 262bus and the system. 263The maximum size of a transfer is governed by the 264adapter. 265Most adapters can transfer 64KB in a single operation, however 266many can transfer larger amounts. 267.Sh TARGET MODE 268Some adapters support 269.Em target mode 270in which the system is capable of operating as a device, responding to 271operations initiated by another system. 272Target mode is supported for 273some adapters, but is not yet complete for this version of the 274.Nm 275.Tn SCSI 276subsystem. 277.Sh FILES 278see other 279.Nm 280device entries. 281.Sh DIAGNOSTICS 282An XPT_DEBUG CCB can be used to enable various amounts of tracing information 283on any specific bus/device from the list of options compiled into the kernel. 284There are currently seven debugging flags that may be compiled in and used: 285.Bl -tag -width CAM_DEBUG_SUBTRACE 286.It Dv CAM_DEBUG_INFO 287This flag enables general informational printfs for the device 288or devices in question. 289.It Dv CAM_DEBUG_TRACE 290This flag enables function-level command flow tracing i.e., 291kernel printfs will happen at the entrance and exit of various functions. 292.It Dv CAM_DEBUG_SUBTRACE 293This flag enables debugging output internal to various functions. 294.It Dv CAM_DEBUG_CDB 295This flag will cause the kernel to print out all 296.Tn ATA 297and 298.Tn SCSI 299commands sent to a particular device or devices. 300.It Dv CAM_DEBUG_XPT 301This flag will enable command scheduler tracing. 302.It Dv CAM_DEBUG_PERIPH 303This flag will enable peripheral drivers messages. 304.It Dv CAM_DEBUG_PROBE 305This flag will enable devices probe process tracing. 306.El 307.Pp 308Some of these flags, most notably 309.Dv CAM_DEBUG_TRACE 310and 311.Dv CAM_DEBUG_SUBTRACE , 312will produce kernel printfs in EXTREME numbers. 313.Pp 314Users can enable debugging from their kernel config file, by using 315the following kernel config options: 316.Bl -tag -width CAM_DEBUG_COMPILE 317.It Dv CAMDEBUG 318This builds into the kernel all possible 319.Nm 320debugging. 321.It Dv CAM_DEBUG_COMPILE 322This allows to specify support for which debugging flags described above 323should be built into the kernel. 324Flags may be ORed together if the user wishes to 325see printfs for multiple debugging levels. 326.It Dv CAM_DEBUG_FLAGS 327This allows to set the various debugging flags from a kernel config file. 328.It Dv CAM_DEBUG_BUS 329Specify a bus to debug. 330To debug all buses, set this to -1. 331.It Dv CAM_DEBUG_TARGET 332Specify a target to debug. 333To debug all targets, set this to -1. 334.It Dv CAM_DEBUG_LUN 335Specify a lun to debug. 336To debug all luns, set this to -1. 337.El 338.Pp 339Users may also enable debugging on the fly by using the 340.Xr camcontrol 8 341utility, if wanted options built into the kernel. 342See 343.Xr camcontrol 8 344for details. 345.Sh SEE ALSO 346.Xr ada 4 , 347.Xr aha 4 , 348.Xr ahc 4 , 349.Xr ahci 4 , 350.Xr ahd 4 , 351.Xr ata 4 , 352.Xr bt 4 , 353.Xr cd 4 , 354.Xr ch 4 , 355.Xr da 4 , 356.Xr nda 4 , 357.Xr nvme 4 , 358.Xr pass 4 , 359.Xr pt 4 , 360.Xr sa 4 , 361.Xr xpt 4 , 362.Xr camcontrol 8 363.Sh HISTORY 364The 365.Nm 366.Tn SCSI 367subsystem first appeared in 368.Fx 3.0 . 369The 370.Nm 371ATA support was added in 372.Fx 8.0 . 373.Sh AUTHORS 374.An -nosplit 375The 376.Nm 377.Tn SCSI 378subsystem was written by 379.An Justin Gibbs 380and 381.An Kenneth Merry . 382The 383.Nm 384.Tn ATA 385support was added by 386.An Alexander Motin Aq Mt mav@FreeBSD.org . 387The 388.Nm 389.Tn NVMe 390support was added by 391.An Warner Losh Aq Mt imp@FreeBSD.org . 392