Document the USB task API

OK mpi@

change post OK:
 - long lines in the source file wrapped
 - added note about USB_TASK_TYPE_ABORT from mpi@

2 files changed, 120 insertions, 3 deletions

diff --git a/share/man/man9/Makefile b/share/man/man9/Makefile
index a9a83b2f0e5..de8cf732dde 100644
--- a/share/man/man9/Makefile
+++ b/share/man/man9/Makefile
@@ -1,4 +1,4 @@
-#	$OpenBSD: Makefile,v 1.280 2016/09/05 07:22:29 dlg Exp $
+#	$OpenBSD: Makefile,v 1.281 2016/09/15 17:53:38 awolk Exp $
 #	$NetBSD: Makefile,v 1.4 1996/01/09 03:23:01 thorpej Exp $
 
 #	Makefile for section 9 (kernel function and variable) manual pages.
@@ -33,8 +33,8 @@ MAN=	aml_evalnode.9 atomic_add_int.9 atomic_cas_uint.9 \
 	spl.9 srp_enter.9 srpl_rc_init.9 startuphook_establish.9 \
 	socreate.9 sosplice.9 style.9 syscall.9 sysctl_int.9 \
 	task_add.9 tc_init.9 time_second.9 timeout.9 tsleep.9 tvtohz.9 \
-	uiomove.9 uvm.9 usbd_close_pipe.9 usbd_open_pipe.9 usbd_ref_wait.9 \
-	usbd_transfer.9 vfs.9 vfs_busy.9 \
+	uiomove.9 uvm.9 usb_add_task.9 usbd_close_pipe.9 usbd_open_pipe.9 \
+	usbd_ref_wait.9 usbd_transfer.9 vfs.9 vfs_busy.9 \
 	vfs_cache.9 vaccess.9 vclean.9 vcount.9 vdevgone.9 vfinddev.9 vflush.9 \
 	vflushbuf.9 vget.9 vgone.9 vhold.9 vinvalbuf.9 vnode.9 vnsubr.9 \
 	VOP_LOOKUP.9 vput.9 vrecycle.9 vref.9 vrele.9 \
diff --git a/share/man/man9/usb_add_task.9 b/share/man/man9/usb_add_task.9
new file mode 100644
index 00000000000..861651d79b0
--- /dev/null
+++ b/share/man/man9/usb_add_task.9
@@ -0,0 +1,117 @@
+.\"	$OpenBSD: usb_add_task.9,v 1.1 2016/09/15 17:53:38 awolk Exp $
+.\"
+.\" Copyright (c) 2016 Adam Wolk <awolk@openbsd.org>
+.\"
+.\" Permission to use, copy, modify, and distribute this software for any
+.\" purpose with or without fee is hereby granted, provided that the above
+.\" copyright notice and this permission notice appear in all copies.
+.\"
+.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+.\"
+.Dd $Mdocdate: September 15 2016 $
+.Dt USB_ADD_TASK 9
+.Os
+.Sh NAME
+.Nm usb_add_task ,
+.Nm usb_rem_task ,
+.Nm usb_wait_task ,
+.Nm usb_rem_wait_task ,
+.Nm usb_init_task
+.Nd USB task queues
+.Sh SYNOPSIS
+.In dev/usb/usbdi.h
+.Ft void
+.Fn usb_add_task "struct usbd_device *dev" "struct usb_task *task"
+.Ft void
+.Fn usb_rem_task "struct usbd_device *dev" "struct usb_task *task"
+.Ft void
+.Fn usb_wait_task "struct usbd_device *dev" "struct usb_task *task"
+.Ft void
+.Fn usb_rem_wait_task "struct usbd_device *dev" "struct usb_task *task"
+.Ft void
+.Fn usb_init_task "struct usbd_device *dev" "void (*fn)(void *)" "void *arg" "char type"
+.Sh DESCRIPTION
+The USB stack provides an API to manage task execution in a thread context at
+the soonest opportunity.  There are three different task queues that are
+executed on two separate threads.  All tasks executed via the USB task API are
+serialized with USB events such as device detachments.
+.Pp
+The
+.Fn usb_add_task
+function enqueues a task to be executed by the task thread.
+Subsequent calls to
+.Fn usb_add_task
+will not result in multiple executions being scheduled.
+The task structure must already be initialised by
+.Fn usb_init_task .
+.Pp
+The
+.Fn usb_rem_task
+function removes a scheduled task from its queue.
+If the work was already executed or has not been added to the task queue,
+the call will have no effect.
+Calling
+.Fn usb_rem_task
+while the task is executing will not abort it.
+.Pp
+The
+.Fn usb_wait_task
+function sleeps until the given task is neither queued for execution
+nor currently running.
+.Pp
+The
+.Fn usb_rem_wait_task
+function is the equivalent of calling
+.Fn usb_rem_task
+followed by
+.Fn usb_wait_task .
+.Pp
+The
+.Fn usb_init_task
+macro prepares the task structure
+.Fa task
+to be used in future calls to
+.Fn usb_add_task ,
+.Fn usb_rem_task ,
+.Fn usb_wait_task ,
+and
+.Fn usb_rem_wait_task .
+.Fa task
+will be prepared to call the function
+.Fa fn
+with the argument specified by
+.Fa arg .
+The
+.Fa type
+of the task determines the queue and thread that will be used for its execution:
+.Bl -tag -width "USB_TASK_TYPE_EXPLORE" -offset indent
+.It Dv USB_TASK_TYPE_GENERIC
+Tasks used for general work that needs to happen in a process context.
+.It Dv USB_TASK_TYPE_EXPLORE
+Device discovery tasks exploring the tree from the root.
+.It Dv USB_TASK_TYPE_ABORT
+Tasks of this type execute on a dedicated thread
+not shared with other USB task types.
+.El
+.Pp
+Most drivers will only define tasks of type
+.Dv USB_TASK_TYPE_GENERIC .
+Note that
+.Dv USB_TASK_TYPE_ABORT
+tasks are only used by Host Controller Drivers and should never be used by
+drivers.  Once initialised, the
+.Fa task
+can be used repeatedly in the API functions listed above and does not need to be
+reinitialised unless the function called and/or its argument must change.
+.Sh CONTEXT
+.Fn usb_task_add
+can be called from any context.
+.Sh SEE ALSO
+.Xr usb 4 ,
+.Xr task_add 9