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 January 15, 2017 28.Dt CAM 4 29.Os 30.Sh NAME 31.Nm CAM 32.Nd Common Access Method SCSI/ATA 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 58and 59.Tn ATA 60devices, and to utilize different 61.Tn SCSI 62and 63.Tn ATA 64host adapters through host adapter drivers. 65When the system probes buses, it attaches any devices it finds to the 66appropriate drivers. 67The 68.Xr pass 4 69driver, if it is configured in the kernel, will attach to all devices. 70.Sh KERNEL CONFIGURATION 71There are a number of generic kernel configuration options for the 72.Nm 73subsystem: 74.Bl -tag -width SCSI_NO_SENSE_STRINGS 75.It Dv CAMDEBUG 76This option compiles in all the 77.Nm 78debugging printf code. 79This will not actually 80cause any debugging information to be printed out when included by itself. 81See below for details. 82.It Dv "CAM_MAX_HIGHPOWER=4" 83This sets the maximum allowable number of concurrent "high power" commands. 84A "high power" command is a command that takes more electrical power than 85most to complete. 86An example of this is the 87.Tn SCSI 88START UNIT command. 89Starting a disk often takes significantly more electrical power than normal 90operation. 91This option allows the 92user to specify how many concurrent high power commands may be outstanding 93without overloading the power supply on his computer. 94.It Dv SCSI_NO_SENSE_STRINGS 95This eliminates text descriptions of each 96.Tn SCSI 97Additional Sense Code and Additional Sense Code Qualifier pair. 98Since this 99is a fairly large text database, eliminating it reduces the size of the 100kernel somewhat. 101This is primarily necessary for boot floppies and other 102low disk space or low memory space environments. 103In most cases, though, 104this should be enabled, since it speeds the interpretation of 105.Tn SCSI 106error messages. 107Do not let the "kernel bloat" zealots get to you -- leave 108the sense descriptions in your kernel! 109.It Dv SCSI_NO_OP_STRINGS 110This disables text descriptions of each 111.Tn SCSI 112opcode. 113This option, like the sense string option above, is primarily 114useful for environments like a boot floppy where kernel size is critical. 115Enabling this option for normal use is not recommended, since it slows 116debugging of 117.Tn SCSI 118problems. 119.It Dv SCSI_DELAY=8000 120This is the 121.Tn SCSI 122"bus settle delay." 123In 124.Nm , 125it is specified in 126.Em milliseconds , 127not seconds like the old 128.Tn SCSI 129layer used to do. 130When the kernel boots, it sends a bus reset to each 131.Tn SCSI 132bus to tell each device to reset itself to a default set of transfer 133negotiations and other settings. 134Most 135.Tn SCSI 136devices need some amount of time to recover from a bus reset. 137Newer disks 138may need as little as 100ms, while old, slow devices may need much longer. 139If the 140.Dv SCSI_DELAY 141is not specified, it defaults to 2 seconds. 142The minimum allowable value for 143.Dv SCSI_DELAY 144is "100", or 100ms. 145One special case is that if the 146.Dv SCSI_DELAY 147is set to 0, that will be taken to mean the "lowest possible value." 148In that case, the 149.Dv SCSI_DELAY 150will be reset to 100ms. 151.El 152.Pp 153All devices and buses support dynamic allocation so that 154an upper number of devices and controllers does not need to be configured; 155.Cd "device da" 156will suffice for any number of disk drivers. 157.Pp 158The devices are either 159.Em wired 160so they appear as a particular device unit or 161.Em counted 162so that they appear as the next available unused unit. 163.Pp 164Units are wired down by setting kernel environment hints. 165This is usually done either interactively from the 166.Xr loader 8 , 167or automatically via the 168.Pa /boot/device.hints 169file. 170The basic syntax is: 171.Bd -literal -offset indent 172hint.device.unit.property="value" 173.Ed 174.Pp 175Individual 176.Nm 177bus numbers can be wired down to specific controllers with 178a config line similar to the following: 179.Bd -literal -offset indent 180hint.scbus.0.at="ahd1" 181.Ed 182.Pp 183This assigns 184.Nm 185bus number 0 to the 186.Em ahd1 187driver instance. 188For controllers supporting more than one bus, a particular bus can be assigned 189as follows: 190.Bd -literal -offset indent 191hint.scbus.0.at="ahc1" 192hint.scbus.0.bus="1" 193.Ed 194.Pp 195This assigns 196.Nm 197bus 0 to the bus 1 instance on 198.Em ahc1 . 199Peripheral drivers can be wired to a specific bus, target, and lun as so: 200.Bd -literal -offset indent 201hint.da.0.at="scbus0" 202hint.da.0.target="0" 203hint.da.0.unit="0" 204.Ed 205.Pp 206This assigns 207.Em da0 208to target 0, unit (lun) 0 of scbus 0. 209Omitting the target or unit hints will instruct 210.Nm 211to treat them as wildcards 212and use the first respective counted instances. 213These examples can be combined together to allow a peripheral device to be 214wired to any particular controller, bus, target, and/or unit instance. 215.Pp 216When you have a mixture of wired down and counted devices then the 217counting begins with the first non-wired down unit for a particular 218type. 219That is, if you have a disk wired down as 220.Em "device da1" , 221then the first non-wired disk shall come on line as 222.Em da2 . 223.Sh ADAPTERS 224The system allows common device drivers to work through many different 225types of adapters. 226The adapters take requests from the upper layers and do 227all IO between the 228.Tn SCSI 229or 230.Tn ATA 231bus and the system. 232The maximum size of a transfer is governed by the 233adapter. 234Most adapters can transfer 64KB in a single operation, however 235many can transfer larger amounts. 236.Sh TARGET MODE 237Some adapters support 238.Em target mode 239in which the system is capable of operating as a device, responding to 240operations initiated by another system. 241Target mode is supported for 242some adapters, but is not yet complete for this version of the 243.Nm 244.Tn SCSI 245subsystem. 246.Sh FILES 247see other 248.Nm 249device entries. 250.Sh DIAGNOSTICS 251An XPT_DEBUG CCB can be used to enable various amounts of tracing information 252on any specific bus/device from the list of options compiled into the kernel. 253There are currently seven debugging flags that may be compiled in and used: 254.Bl -tag -width CAM_DEBUG_SUBTRACE 255.It Dv CAM_DEBUG_INFO 256This flag enables general informational printfs for the device 257or devices in question. 258.It Dv CAM_DEBUG_TRACE 259This flag enables function-level command flow tracing i.e., 260kernel printfs will happen at the entrance and exit of various functions. 261.It Dv CAM_DEBUG_SUBTRACE 262This flag enables debugging output internal to various functions. 263.It Dv CAM_DEBUG_CDB 264This flag will cause the kernel to print out all 265.Tn ATA 266and 267.Tn SCSI 268commands sent to a particular device or devices. 269.It Dv CAM_DEBUG_XPT 270This flag will enable command scheduler tracing. 271.It Dv CAM_DEBUG_PERIPH 272This flag will enable peripheral drivers messages. 273.It Dv CAM_DEBUG_PROBE 274This flag will enable devices probe process tracing. 275.El 276.Pp 277Some of these flags, most notably 278.Dv CAM_DEBUG_TRACE 279and 280.Dv CAM_DEBUG_SUBTRACE , 281will produce kernel printfs in EXTREME numbers. 282.Pp 283Users can enable debugging from their kernel config file, by using 284the following kernel config options: 285.Bl -tag -width CAM_DEBUG_COMPILE 286.It Dv CAMDEBUG 287This builds into the kernel all possible 288.Nm 289debugging. 290.It Dv CAM_DEBUG_COMPILE 291This allows to specify support for which debugging flags described above 292should be built into the kernel. 293Flags may be ORed together if the user wishes to 294see printfs for multiple debugging levels. 295.It Dv CAM_DEBUG_FLAGS 296This allows to set the various debugging flags from a kernel config file. 297.It Dv CAM_DEBUG_BUS 298Specify a bus to debug. 299To debug all buses, set this to -1. 300.It Dv CAM_DEBUG_TARGET 301Specify a target to debug. 302To debug all targets, set this to -1. 303.It Dv CAM_DEBUG_LUN 304Specify a lun to debug. 305To debug all luns, set this to -1. 306.El 307.Pp 308Users may also enable debugging on the fly by using the 309.Xr camcontrol 8 310utility, if wanted options built into the kernel. 311See 312.Xr camcontrol 8 313for details. 314.Sh SEE ALSO 315.Xr ada 4 , 316.Xr aha 4 , 317.Xr ahc 4 , 318.Xr ahci 4 , 319.Xr ahd 4 , 320.Xr ata 4 , 321.Xr bt 4 , 322.Xr cd 4 , 323.Xr ch 4 , 324.Xr da 4 , 325.Xr pass 4 , 326.Xr pt 4 , 327.Xr sa 4 , 328.Xr xpt 4 , 329.Xr camcontrol 8 330.Sh HISTORY 331The 332.Nm 333.Tn SCSI 334subsystem first appeared in 335.Fx 3.0 . 336The 337.Nm 338ATA support was added in 339.Fx 8.0 . 340.Sh AUTHORS 341.An -nosplit 342The 343.Nm 344.Tn SCSI 345subsystem was written by 346.An Justin Gibbs 347and 348.An Kenneth Merry . 349The 350.Nm 351.Tn ATA 352support was added by 353.An Alexander Motin Aq Mt mav@FreeBSD.org . 354