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AHCI(4)		       FreeBSD Kernel Interfaces Manual		       AHCI(4)

     ahci -- Serial ATA	Advanced Host Controller Interface driver

     To	compile	this driver into the kernel, place the following lines in your
     kernel configuration file:

	   device pci
	   device scbus
	   device ahci

     Alternatively, to load the	driver as a module at boot time, place the
     following line in loader.conf(5):


     The following tunables are	settable from the loader(8):

     controls Message Signaled Interrupts (MSI)	usage by the specified con-

	   0	 MSI disabled;
	   1	 single	MSI vector used, if supported;
	   2	 multiple MSI vectors used, if supported (default);

     controls Command Completion Coalescing (CCC) usage	by the specified con-
     troller.  Non-zero	value enables CCC and defines maximum time (in ms),
     request can wait for interrupt, if	there are some more requests present
     on	controller queue.  CCC reduces number of context switches on systems
     with many parallel	requests, but it can decrease disk performance on some
     workloads due to additional command latency.
     controls whether the driver should	use direct command completion from in-
     terrupt thread(s),	or queue them to CAM completion	threads.  Default
     value depends on number of	MSI interrupts supported and number of imple-
     mented SATA ports.

     controls whether the driver should	implement virtual enclosure management
     device on top of SGPIO or other interface.	 Default value depends on con-
     troller capabilities.

     controls SATA interface Power Management for the specified	channel, al-
     lowing some power to be saved at the cost of additional command latency.
     Possible values:

	   0	 interface Power Management is disabled	(default);
	   1	 device	is allowed to initiate PM state	change,	host is	pas-
	   2	 host initiates	PARTIAL	PM state transition every time port
		 becomes idle;
	   3	 host initiates	SLUMBER	PM state transition every time port
		 becomes idle.
	   4	 driver	initiates PARTIAL PM state transition 1ms after	port
		 becomes idle;
	   5	 driver	initiates SLUMBER PM state transition 125ms after port
		 becomes idle.

     Some controllers, such as ICH8, do	not implement modes 2 and 3 with NCQ
     used.  Because of artificial entering latency, performance	degradation in
     modes 4 and 5 is much smaller then	in modes 2 and 3.

     Note that interface Power Management complicates device presence detec-
     tion.  A manual bus reset/rescan may be needed after device hot-plug, un-
     less hardware implements Cold Presence Detection.

     setting to	nonzero	value limits maximum SATA revision (speed).  Values 1,
     2 and 3 are respectively 1.5, 3 and 6Gbps.

     setting to	nonzero	value forces driver attach to some known AHCI-capable
     chips even	if they	are configured for legacy IDE emulation.  Default is

     This driver provides the CAM(4) subsystem with native access to the SATA
     ports of AHCI-compatible controllers.  Each SATA port found is repre-
     sented to CAM as a	separate bus with one target, or, if HBA supports Port
     Multipliers, 16 targets.  Most of the bus-management details are handled
     by	the SATA-specific transport of CAM.  Connected ATA disks are handled
     by	the ATA	protocol disk peripheral driver	ada(4).	 ATAPI devices are
     handled by	the SCSI protocol peripheral drivers cd(4), da(4), sa(4), etc.

     Driver features include support for Serial	ATA and	ATAPI devices, Port
     Multipliers (including FIS-based switching, when supported), hardware
     command queues (up	to 32 commands per port), Native Command Queuing, SATA
     interface Power Management, device	hot-plug and Message Signaled Inter-

     Driver supports "LED" enclosure management	messages, defined by the AHCI.
     When supported by hardware, it allows to control per-port activity, lo-
     cate and fault LEDs via the led(4)	API or emulated	ses(4) device for lo-
     calization	and status reporting purposes.	Supporting AHCI	controllers
     may transmit that information to the backplane controllers	via SGPIO in-
     terface.  Backplane controllers interpret received	statuses in some way
     (IBPI standard) to	report them using present indicators.

     The ahci driver supports AHCI compatible controllers having PCI class 1
     (mass storage), subclass 6	(SATA) and programming interface 1 (AHCI).

     Also, in cooperation with atamarvell and atajmicron drivers of ata(4), it
     supports AHCI part	of legacy-PATA + AHCI-SATA combined controllers, such
     as	JMicron	JMB36x and Marvell 88SE61xx.

     The ahci driver also supports AHCI	devices	that act as PCI	bridges	for
     nvme(4) using Intel Rapid Storage Technology (RST).  To use the nvme(4)
     device, either one	must set the SATA mode in the BIOS to AHCI (from RST),
     or	one must accept	the performance	with RST enabled due to	interrupt
     sharing.  FreeBSD will automatically detect AHCI devices with this	exten-
     sion that are in RST mode.	 When that happens, ahci will attach nvme(4)
     children to the ahci(4) device.

     /dev/led/ahci*.*.act     activity LED device nodes

     /dev/led/ahci*.*.fault   fault LED	device nodes

     /dev/led/ahci*.*.locate  locate LED device	nodes

	     Set to 1 to disable the phy for the drive on channel X.  Set to 0
	     to	enable the phy.	 Useful	for turning off	troublemakers.	Also
	     useful for	debugging when you need	the ada	drive to come and go.

     ada(4), ata(4), cam(4), cd(4), da(4), sa(4), ses(4)

     The ahci driver first appeared in FreeBSD 8.0.

     Alexander Motin <>

FreeBSD	13.0		       December	17, 2021		  FreeBSD 13.0


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