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.\" Copyright 2016 Joyent, Inc.
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.Dd November 18, 2016
.Dt USBA_HCDI 9E
.Os
.Sh NAME
.Nm usba_hcdi
.Nd USB Host Controller Driver Interface
.Sh SYNOPSIS
.In sys/usb/usba/hcdi.h
.Sh INTERFACE LEVEL
.Sy Volatile -
illumos USB HCD private function
.Pp
This describes private interfaces that are not part of the stable DDI.
This may be removed or changed at any time.
.Sh DESCRIPTION
.Sy hcdi
drivers are device drivers that support USB host controller hardware.
USB host controllers provide an interface between the operating system
and USB devices.
They abstract the interface to the devices, often provide ways of performing
DMA, and also act as the root hub.
.Pp
.Sy hcdi
drivers are part of the illumos USB Architecture (USBA).
The
.Xr usba 7D
driver provides support for many of the surrounding needs of an
.Sy hcdi
driver and requires that such drivers implement a specific operations
vector,
.Xr usba_hcdi_ops 9S .
These functions cover everything from initialization to performing I/O
to USB devices on behalf of client device drivers.
.Ss USB Speed and Version Background
USB devices are often referred to in two different ways.
The first way is the USB version that they conform to.
In the wild this looks like USB 1.1, USB 2.0, USB 3.0, etc..
However, devices are also referred to as
.Sq full- ,
.Sq low- ,
.Sq high- ,
.Sq super-
speed devices.
.Pp
The latter description describes the maximum theoretical speed of a
given device.
For example, a super-speed device theoretically caps out around 5 Gbit/s,
whereas a low-speed device caps out at 1.5 Mbit/s.
.Pp
In general, each speed usually corresponds to a specific USB protocol
generation.
For example, all USB 3.0 devices are super-speed devices.
All 'high-speed' devices are USB 2.x devices.
Full-speed devices are special in that they can either be USB 1.x or USB 2.x
devices.
Low-speed devices are only a USB 1.x thing, they did not jump the fire line to
USB 2.x.
.Pp
USB 3.0 devices and ports generally have the wiring for both USB 2.0 and
USB 3.0.
When a USB 3.0 device is plugged into a USB 2.0 port or hub, then it will report
its version as USB 2.1, to indicate that it is actually a USB 3.0 device.
.Ss USB Endpoint Background
To understand the organization of the functions that make up the hcdi
operations vector, it helps to understand how USB devices are organized
and work at a high level.
.Pp
A given USB device is made up of
.Em endpoints .
A request, or transfer, is made to a specific USB endpoint.
These endpoints can provide different services and have different expectations
around the size of the data that'll be used in a given request and the
periodicity of requests.
Endpoints themselves are either used to make one-shot requests, for example,
making requests to a mass storage device for a given sector, or for making
periodic requests where you end up polling on the endpoint, for example, polling
on a USB keyboard for keystrokes.
.Pp
Each endpoint encodes two different pieces of information: a direction
and a type.
There are two different directions: IN and OUT.
These refer to the general direction that data moves relative to the operating
system.
For example, an IN transfer transfers data in to the operating system, from the
device.
An OUT transfer transfers data from the operating system, out to the device.
.Pp
There are four different kinds of endpoints:
.Bl -tag -width Sy -offset indent
.It Sy BULK
These transfers are large transfers of data to or from a device.
The most common use for bulk transfers is for mass storage devices.
Though they are often also used by network devices and more.
Bulk endpoints do not have an explicit time component to them.
They are always used for one-shot transfers.
.It Sy CONTROL
These transfers are used to manipulate devices themselves and are used
for USB protocol level operations (whether device-specific,
class-specific, or generic across all of USB).
Unlike other transfers, control transfers are always bi-directional and use
different kinds of transfers.
.It Sy INTERRUPT
Interrupt transfers are used for small transfers that happen
infrequently, but need reasonable latency.
A good example of interrupt transfers is to receive input from a USB keyboard.
Interrupt-IN transfers are generally polled.
Meaning that a client (device driver) opens up an interrupt-IN endpoint to poll
on it, and receives periodic updates whenever there is information available.
However, Interrupt transfers can be used as one-shot transfers both going IN and
OUT.
.It Sy ISOCHRONOUS
These transfers are things that happen once per time-interval at a very
regular rate.
A good example of these transfers are for audio and video.
A device may describe an interval as 10ms at which point it will read or
write the next batch of data every 10ms and transform it for the user.
There are no one-shot Isochronous-IN transfers.
There are one-shot Isochronous-OUT transfers, but these are used by device
drivers to always provide the system with sufficient data.
.El
.Pp
To find out information about the endpoints, USB devices have a series
of descriptors that cover different aspects of the device.
For example, there are endpoint descriptors which cover the properties of
endpoints such as the maximum packet size or polling interval.
.Pp
Descriptors exist at all levels of USB.
For example, there are general descriptors for every device.
The USB device descriptor is described in
.Xr usb_dev_descr 9S .
Host controllers will look at these descriptors to ensure that they
program the device correctly; however, they are more often used by
client device drivers.
There are also descriptors that exist at a class level.
For example, the hub class has a class-specific descriptor which describes
properties of the hub.
That information is requested for and used by the hub driver.
.Pp
All of the different descriptors are gathered by the system and placed
into a tree, with device descriptors, configurations, endpoints, and
more.
Client device drivers gain access to this tree and then use them to then open
endpoints, which are called pipes in USBA (and some revisions of the USB
specification).
.Pp
Each pipe gives access to a specific endpoint on the device which can be
used to perform transfers of a specific type and direction.
For example, a mass storage device often has three different endpoints, the
default control endpoint (which every device has), a Bulk-IN endpoint, and a
Bulk-OUT endpoint.
The device driver ends up with three open pipes.
One to the default control endpoint to configure the device, and then the
other two are used to perform I/O.
.Pp
These routines translate more or less directly into calls to a host
controller driver.
A request to open a pipe takes an endpoint descriptor that describes the
properties of the pipe, and the host controller driver goes through and does any
work necessary to allow the client device driver to access it.
Once the pipe is open, it either makes one-shot transfers specific to the
transfer type or it starts performing a periodic poll of an endpoint.
.Pp
All of these different actions translate into requests to the host
controller.
The host controller driver itself is in charge of making sure that all of the
required resources for polling are allocated with a request and then proceed to
give the driver's periodic callbacks.
.Pp
For each of the different operations described above, there is a corresponding
entry in
.Xr usba_hcdi_ops 9S .
For example, open an endpoint, the host controller has to implement
.Xr usba_hcdi_pipe_open 9E
and for each transfer type, there is a different transfer function.
One example is
.Xr usba_hcdi_pipe_bulk_xfer 9E .
See
.Xr usba_hcdi_ops 9S
for a full list of the different function endpoints.
.Ss HCDI Initialization
hcdi drivers are traditional character device drivers.
To start with, an hcdi driver should define traditional
.Xr dev_ops 9S
and
.Xr cb_ops 9S
structures.
To get started, the device driver should perform normal device initialization in
an
.Xr attach 9E
entry point.
For example, PCI devices should setup the device's registers and program them.
In addition, all devices should configure interrupts, before getting ready to
call into the USBA.
Each instance of a device must be initialized and registered with the USBA.
.Pp
To initialize a device driver with the USBA, it must first call
.Xr usba_alloc_hcdi_ops 9F .
This provides a device driver with the
.Xr usba_hcdi_ops 9S
structure that it must fill out.
Please see
.Xr usba_hcdi_ops 9S
for instructions on how it should be filled out.
Once filled out, the driver should call
.Xr usba_hcdi_register 9F .
.Pp
If the call to register fails for whatever reason, the device driver
should fail its
.Xr attach 9E
entry point.
After this call successfully completes, the driver should assume that any of the
functions it registered with the call to
.Xr usba_hcdi_register 9F
will be called at this point.
.Ss Binding the Root Hub
Once this is set up, the hcdi driver must initialize its root hub by
calling
.Xr usba_hubdi_bind_root_hub 9F .
To bind the root hub, the device driver is responsible for providing a
device descriptor that represents the hardware.
Depending on the hardware, this descriptor may be either static or dynamic.
.Pp
This device descriptor should be a packed descriptor that is the same
that would be read off of the device.
The device descriptor should match a hub of a USB generation equivalent to the
maximum speed of the device.
For example, a USB 3.0 host controller would use a USB 3.0 hub's device
descriptor.
Similarly, a USB 2.0 host controller would use a USB 2.0 hub's device
descriptor.
.Pp
The descriptor first starts with a USB configuration descriptor, as
defined in
.Xr usb_cfg_descr 9S .
It is then followed by an interface descriptor.
The definition for it can be found in
.Xr usb_if_descr 9S .
Next is the endpoint descriptor for the single Interrupt-IN endpoint
that all hubs have as defined in
.Xr usb_ep_descr 9S .
Finally, any required companion descriptors should be used.
For example, a USB 3.x hub will have a
.Xr usb_ep_ss_comp_descr 9S
appended to the structure.
.Pp
Note, that the structure needs to be packed, as though it were read from
a device.
The structures types referenced in
.Xr usb_cfg_descr 9S ,
.Xr usb_if_descr 9S ,
.Xr usb_ep_descr 9S ,
and
.Xr usb_ep_ss_comp_descr 9S
are not packed for this purpose.
They should not be used as they have gaps added by the compiler for alignment.
.Pp
Once assembled, the device driver should call
.Xr usba_hubdi_bind_root_hub 9F .
This will cause an instance of the
.Xr hubd 7D
driver to be attached and associated with the root controller.
As such, driver writers need to ensure that all initialization is done prior to
loading the root hub.
Once successfully loaded, driver writers should assume that they'll get other
calls into the driver's operation vector before the call to
.Xr usba_hubdi_bind_root_hub 9F .
.Pp
If the call to
.Xr usba_hubdi_bind_root_hub 9F
failed for whatever reason, the driver should unregister from USBA (see
the next section), unwind all of the resources it has allocated, and
return
.Dv DDI_FAILURE .
.Pp
Otherwise, at this point it's safe to assume that the instance of the
device has initialized successfully and the driver should return
.Dv DDI_SUCCESS .
.Ss Driver Teardown
When a driver's
.Xr detach 9E
entry point has been called, before anything else is done, the device
driver should unbind its instance of the root hub and then unregister
from the USBA.
.Pp
To unbind the root hub, the instance of the driver should call
.Xr usba_hubdi_unbind_root_hub 9F .
If for some reason that function does not return
.Sy USB_SUCCESS ,
then the device driver should fail the call to
.Xr detach 9E
and return
.Dv DDI_FAILURE .
.Pp
Once the root hub has been unbound, the device driver can continue by
removing its hcdi registration with USBA.
To do this, the driver should call
.Xr usba_hcdi_unregister 9F .
As this call always succeeds, at this point, it is safe for the driver
to tear down all the rest of its resources and successfully detach.
.Ss State Tracking and Minor Numbers
Because a host controller driver is also a root hub, there are a few
constraints around how the device must store its per-instance state and
how its minor numbers are used.
.Pp
hcdi drivers
.Em must not
store any data with
.Xr ddi_get_driver_private 9F .
This private data is used by USBA.
If it has been called before the device registers, then it will fail to register
successfully with the USBA.
However, setting it after that point will corrupt the state of the USBA and
likely lead to data corruption and crashes.
.Pp
Similarly, part of the minor number space is utilized to represent
various devices like the root hub.
Whenever a device driver is presented with a
.Ft dev_t
and it's trying to extract the minor number, it must take into account
the constant
.Dv HUBD_IS_ROOT_HUB .
The following shows how to perform this, given a
.Ft dev_t
called
.Ft dev :
.Bd -literal -offset indent
minor_t minor = getminor(dev) & ~HUBD_IS_ROOT_HUB;
.Ed
.Ss Required Character and Device Operations
The USBA handles many character and device operations entry points for a
device driver or has strict rules on what a device driver must do in
them.
This section summarizes those constraints.
.Pp
In the
.Xr dev_ops 9S
structure, the following members have special significance:
.Bl -tag -offset indent -width Sy
.It Sy devo_bus_ops
The
.Sy devo_bus_ops
member should be set to the symbol
.Sy usba_hubdi_busops .
See
.Xr usba_hubdi_dev_ops 9F
for more information.
.It Sy devo_power
The
.Sy devo_power
member should be set to the symbol
.Sy usba_hubdi_root_hub_power .
See
.Xr usba_hubdi_dev_ops 9F
for more information.
.El
.Pp
The other standard entry points for character devices,
.Sy devo_getinfo ,
.Sy devo_attach ,
and
.Sy devo_detach
should be implemented normally as per
.Xr getinfo 9E ,
.Xr attach 9E ,
and
.Xr detach 9E
respectively.
.Pp
The following members of the
.Xr cb_ops 9S
operations vector must be implemented and set:
.Bl -tag -offset indent -width Sy
.It Sy cb_open
The device driver should implement an
.Xr open 9E
entry point that obtains access to its
.Sy dev_info_t
and then calls
.Xr usba_hubdi_open 9F .
See
.Xr usba_hcdi_cb_open 9E
for more information.
.It Sy cb_close
The device driver should implement a
.Xr close 9E
entry point that obtains access to its
.Sy dev_info_t
and then calls
.Xr usba_hubdi_close 9F .
 See
.Xr usba_hcdi_cb_close 9E
for more information.
.It Sy cb_ioctl
The device driver should implement a
.Xr ioctl 9E
entry point that obtains access to its
.Sy dev_info_t
and then calls
.Xr usba_hubdi_ioctl 9F .
.Pp
If the device driver wishes to have private ioctls, it may check the
ioctl command before calling
.Xr usba_hubdi_ioctl 9F .
Because the
.Xr usba_hubdi_ioctl 9F
function normally takes care of checking for the proper privileges,
device drivers must verify that a caller has appropriate privileges
before processing any private ioctls.
.Pp
See
.Xr usba_hcdi_cb_ioctl 9E
for more information.
.It Sy cb_prop_op
The
.Sy cb_prop_op
member should be set to
.Xr ddi_prop_op 9F .
.It Sy cb_flag
The
.Sy cb_flag
member should be set to the bitwise-inclusive-OR of the
.Sy D_MP
flag
and the
.Sy D_HOTPLUG
flag.
.El
.Pp
All other members of the
.Xr cb_ops 9S
structure should not be implemented and set to the appropriate value,
such as
.Xr nodev 9F
or
.Xr nochpoll 9F .
.Ss Locking
In general, the USBA calls into a device driver through one of the
functions that it has register in the
.Xr usba_hcdi_ops 9S
structure.
However, in response to a data transfer, the device driver will need to call
back into the USBA by calling
.Xr usba_hcdi_cb 9F .
.Pp
A device driver must hold
.Em no locks
across the call to
.Xr usba_hcdi_cb 9F .
Returning an I/O to the USBA, particularly an error, may result in
another call back to one of the
.Xr usba_hcdi_cb 9F
vectors.
.Pp
Outside of that constraint, the device driver should perform locking of
its data structures.
It should assume that many of its entry points will be called in parallel across
the many devices that exist.
.Pp
There are certain occasions where a device driver may have to enter the
.Sy p_mutex
member of the
.Xr usba_pipe_handle_data 9S
structure when duplicating isochronous or interrupt requests.
The USBA should in general, not hold this lock across calls to the HCD driver,
and in turn, the HCD driver should not hold this lock across any calls back to
the USBA.
As such, the HCD driver should make sure to incorporate the lock ordering of
this mutex into its broader lock ordering and operational theory.
Generally, the
.Sy p_mutex
mutex will be entered after any HCD-specific locks.
.Pp
The final recommendation is that due to the fact that the host
controller driver provides services to a multitude of USB devices at
once, it should strive not to hold its own internal locks while waiting
for I/O to complete, such as an issued command.
This is particularly true if the device driver uses coarse grained locking.
If the device driver does not pay attention to these conditions, it can easily
lead to service stalls.
.Ss Synchronous and Asynchronous Entry Points
The majority of the entry points that a host controller driver has to
implement are
.Em synchronous .
All actions that the entry point implies must be completed before the
entry point returns.
However, the various transfer routines:
.Xr usba_hcdi_pipe_bulk_xfer 9E ,
.Xr usba_hcdi_pipe_ctrl_xfer 9E ,
.Xr usba_hcdi_pipe_intr_xfer 9E ,
and
.Xr usba_hcdi_pipe_isoc_xfer 9E ,
are ultimately
.Em asynchronous
entry points.
.Pp
Each of the above entry points begins one-shot or periodic I/O.
When the driver returns
.Sy USB_SUCCESS
from one of those functions, it is expected that it will later call
.Xr usba_hcdi_cb 9F
when the I/O completes, whether successful or not.
It is the driver's responsibility to keep track of these outstanding transfers
and time them out.
For more information on timeouts, see the section
.Sx Endpoint Timeouts .
.Pp
If for some reason, the driver fails to initialize the I/O transfer and
indicates this by returning a value other than
.Sy USB_SUCCESS
from its entry point, then it must not call
.Xr usba_hcdi_cb 9F
for that transfer.
.Ss Short Transfers
Not all USB transfers will always return the full amount of data
requested in the transfer.
Host controller drivers need to be ready for this and report it.
Each request structure has an attribute to indicate whether or not short
transfers are OK.
If a short transfer is OK, then the driver should update the transfer length.
Otherwise, it should instead return an error.
See the individual entry point pages for more information.
.Ss Root Hub Management
As was mentioned earlier, every host controller is also a root hub.
The USBA interfaces with the root hub no differently than any other hub.
The USBA will open pipes and issue both control and periodic interrupt-IN
transfers to the root hub.
.Pp
In the host controller driver's
.Xr usba_hcdi_pipe_open 9E
entry point, it already has to look at the pipe handle it's been given
to determine the attributes of the endpoint it's looking at.
However, before it does that it needs to look at the USB address of the device
the handle corresponds to.
If the device address matches the macro
.Sy ROOT_HUB_ADDR ,
then this is a time where the USBA is opening one of the root hub's
endpoints.
.Pp
Because the root hub is generally not a real device, the driver will
likely need to handle this in a different manner from traditional pipes.
.Pp
The device driver will want to check for the presence of the device's
address with the following major entry points and change its behavior as
described:
.Bl -tag -width Fn
.It Fn usba_hcdi_pipe_ctrl_xfer
The device driver needs to intercept control transfers to the root hub
and translate them into the appropriate form for the device.
For example, the device driver may be asked to get a port's status.
It should determine the appropriate way to perform this, such as reading a
PCI memory-mapped register, and then create the appropriate response.
.Pp
The device driver needs to implement all of the major hub specific
request types.
It is recommended that driver writers see what existing host controller drivers
implement and what the hub driver currently requires to implement this.
.Pp
Aside from the fact that the request is not being issued to a specific
USB device, a request to the root hub follows the normal rules for a
transfer and the device driver will need to call
.Xr usba_hcdi_cb 9F
to indicate that it has finished.
.It Fn usba_hcdi_pipe_bulk_xfer
The root hub does not support bulk transfers.
If for some reason one is requested on the root hub, the driver should return
.Sy USB_NOT_SUPPORTED .
.It Fn usba_hcdi_pipe_intr_xfer
The root hub only supports periodic interrupt-IN transfers.
If an interrupt-OUT transfer or an interrupt-IN transfer with the
.Sy USB_ATTRS_ONE_XFER
attribute is set, then the driver should return
.Sy USB_NOT_SUPPORTED .
.Pp
Otherwise, this represents a request to begin polling on the status
endpoint for a hub.
This is a periodic request, see the section
.Sx Device Addressing
Every USB device has an address assigned to it.
The addresses assigned to each controller are independent.
The root hub of a given controller always has an address of
.Dv ROOT_HUB_ADDR .
.Pp
In general, addresses are assigned by the USBA and stored in the
.Sy usb_addr
member of a
.Xr usba_device_t 9S .
However, some controllers, such as xHCI, require that they control the
device addressing themselves to facilitate their functionality.
In such a case, the USBA still assigns every device an address; however, the
actual address on the bus will be different and assigned by the HCD
driver.
An HCD driver that needs to address devices itself must implement the
.Xr usba_hcdi_device_address 9E
entry point.
.Sx Endpoint Polling
more on the semantics of polling and periodic requests.
.Pp
Here, the device driver will need to provide data and perform a callback
whenever the state of one of the ports changes on its virtual hub.
Different drivers have different ways to perform this.
For example, some hardware will provide an interrupt to indicate that a change
has occurred.
Other hardware does not, so this must be simulated.
.Pp
The way that the status data responses must be laid out is based in the
USB specification.
Generally, there is one bit per port and the driver sets the bit for the
corresponding port that has had a change.
.It Fn usba_hcdi_pipe_isoc_xfer
The root hub does not support isochronous transfers.
If for some reason one is requested on the root hub, the driver should return
.It Fn usba_hcdi_pipe_close
When a pipe to the root hub is closed, the device driver should tear
down whatever it created as part of opening the pipe.
In addition, if the pipe was an interrupt-IN pipe, if it has not already had
polling stop, it should stop the polling as part of closing the pipe.
.It Fn usba_hcdi_pipe_stop_intr_polling
When a request to stop interrupt polling comes in and it is directed
towards the root hub, the device driver should cease delivering
callbacks upon changes in port status being detected.
However, it should continue keeping track of what changes have occurred for the
next time that polling starts.
.Pp
The primary request that was used to start polling should be returned,
as with any other request to stop interrupt polling.
.It Fn usba_hcdi_pipe_stop_isoc_polling
The root hub does not support isochronous transfers.
If for some reason it calls asking to stop polling on an isochronous transfer,
the device driver should log an error and return
.Sy USB_NOT_SUPPORTED .
.El
.Ss Endpoint Polling
Both interrupt-IN and isochronous-IN endpoints are generally periodic or
polled endpoints.
interrupt-IN polling is indicated by the lack of the
.Sy USB_ATTRS_ONE_XFER
flag being set.
All isochronous-IN transfer requests are requests for polling.
.Pp
Polling operates in a different fashion from traditional transfers.
With a traditional transfer, a single request is made and a single callback
is made for it, no more and no less.
With a polling request, things are different.
A single transfer request comes in; however, the driver needs to keep ensuring
that transfers are being made within the polling bounds until a request to stop
polling comes in or a fatal error is encountered.
.Pp
In many cases, as part of initializing the request, the driver will
prepare several transfers such that there is always an active transfer,
even if there is some additional latency in the system.
This ensures that even if there is a momentary delay in the device driver
processing a given transfer, I/O data will not be lost.
.Pp
The driver must not use the original request structure until it is ready
to return due to a request to stop polling or an error.
To obtain new interrupt and isochronous request structures, the driver should
use the
.Xr usba_hcdi_dup_intr_req 9F
and
.Xr usba_hcdi_dup_isoc_req 9F
functions.
These functions also allocate the resulting message blocks that data should be
copied into.
Note, it is possible that memory will not be available to duplicate such a
request.
In this case, the driver should use the original request to return an error and
stop polling.
.Ss Request Memory and DMA
Each of the four transfer operations,
.Xr usba_hcdi_pipe_ctrl_xfer 9E ,
.Xr usba_hcdi_pipe_bulk_xfer 9E ,
.Xr usba_hcdi_pipe_intr_xfer 9E ,
and
.Xr usba_hcdi_pipe_isoc_xfer 9E
give data to hcdi drivers in the form of
.Xr mblk 9S
structures.
To perform the individual transfers, most systems devices will leverage DMA.
Drivers should allocate memory suitable for DMA for each transfer that they need
to perform and copy the data to and from the message blocks.
.Pp
Device drivers should not use
.Xr desballoc 9F
to try and bind the memory used for DMA transfers to a message block nor
should they bind the message block's read pointer to a DMA handle using
.Xr ddi_dma_addr_bind_handle 9F .
.Pp
While this isn't a strict rule, the general framework does not assume
that there are going to be outstanding message blocks that may be in use
by the controller or belong to the controller outside of the boundaries
of a given call to one of the transfer functions and its corresponding
callback.
.Ss Endpoint Timeouts
The host controller is in charge of watching I/Os for timeouts.
For any request that's not periodic (an interrupt-IN or isochronous-IN)
transfer, the host controller must set up a timeout handler.
If that timeout expires, it needs to stop the endpoint, remove that request, and
return to the caller.
.Pp
The timeouts are specified in seconds in the request structures.
For bulk timeouts, the request is in the
.Sy bulk_timeout
member of the
.Xr usb_bulk_req 9S
structure.
The interrupt and control transfers also have a similar member in their request
structures, see
.Xr usb_intr_req 9S
and
.Xr usb_ctrl_req 9S .
If any of the times is set to zero, the default USBA timeout should be
used.
In that case, drivers should set the value to the macro
.Sy HCDI_DEFAULT_TIMEOUT ,
which is a time in seconds.
.Pp
Isochronous-OUT transfers do not have a timeout defined on their request
structure, the
.Xr usb_isoc_req 9S .
Due to the periodic nature of even outbound requests, it is less likely
that a timeout will occur; however, driver writers are encouraged to
still set up the default timeout,
.Sy HCDI_DEFAULT_TIMEOUT ,
on those transfers.
.Pp
The exact means of performing the timeout is best left to the driver
writer as the way that hardware exposes scheduling of different
endpoints will vary.
One strategy to consider is to use the
.Xr timeout 9F
function at a one second period while I/O is ongoing on a per-endpoint
basis.
Because the time is measured in seconds, a driver writer can decrement a counter
for a given outstanding transfer once a second and then if it reaches zero,
interject and stop the endpoint and clean up.
.Pp
This has the added benefit that when no I/O is scheduled, then there
will be no timer activity, reducing overall system load.
.Ss Notable Types and Structures
The following are data structures and types that are used throughout
host controller drivers:
.Bl -tag -width Vt
.It Sy usb_cfg_descr
The configuration descriptor.
A device may have one or more configurations that it supports that can be
switched between.
The descriptor is documented in
.Xr usb_cfg_descr 9S .
.It Sy usb_dev_descr
The device descriptor.
A device descriptor contains basic properties of the device such as the USB
version, device and vendor information, and the maximum packet size.
This will often be used when setting up a device for the first time.
It is documented in
.Xr usb_dev_descr 9S .
.It Sy usb_ep_descr
The endpoint descriptor.
An endpoint descriptor contains the basic properties of an endpoints such as its
type and packet size.
Every endpoint on a given USB device has an endpoint descriptor.
It is documented in
.Xr usb_ep_descr 9S .
.It Sy usb_xep_descr
The extended endpoint descriptor.
This structure is used to contain the endpoint descriptor, but also additional
endpoint companion descriptors which are a part of newer USB standards.
It is documented in
.Xr usb_ep_xdescr 9S .
.It Sy usb_bulk_req
This structure is filled out by client device drivers that want to make
a bulk transfer request.
Host controllers use this and act on it to perform bulk transfers to USB
devices.
The structure is documented in
.Xr usb_bulk_req 9S .
.It Sy usb_ctrl_req
This structure is filled out by client device drivers that want to make
a control transfer request.
Host controllers use this and act on it to perform bulk transfers to USB
devices.
The structure is documented in
.Xr usb_ctrl_req 9S .
.It Sy usb_intr_req
This structure is filled out by client device drivers that want to make
an interrupt transfer request.
Host controllers use this and act on it to perform bulk transfers to USB
devices.
The structure is documented in
.Xr usb_intr_req 9S .
.It Sy usb_isoc_req
This structure is filled out by client device drivers that want to make
an isochronous transfer request.
Host controllers use this and act on it to perform bulk transfers to USB
devices.
The structure is documented in
.Xr usb_isoc_req 9S .
.It Vt usb_flags_t
These define a set of flags that are used on certain entry points.
These generally determine whether or not the entry points should block for
memory allocation.
Individual manual pages indicate the flags that drivers should consult.
.It Vt usb_port_status_t
The
.Sy usb_port_status_t
determines the current negotiated speed of the device.
The following are valid values that this may be:
.Bl -tag -width Sy
.It Sy USBA_LOW_SPEED_DEV
The device is running as a low speed device.
This may be a USB 1.x or USB 2.0 device.
.It Sy USBA_FULL_SPEED_DEV
The device is running as a full speed device.
This may be a USB 1.x or USB 2.0 device.
.It Sy USBA_HIGH_SPEED_DEV
The device is running as a high speed device.
This is a USB 2.x device.
.It Sy USBA_SUPER_SPEED_DEV
The device is running as a super speed device.
This is a USB 3.0 device.
.It Vt usb_cr_t
This is a set of codes that may be returned as a part of the call to
.Xr usba_hcdi_cb 9F .
The best place for the full set of these is currently in the source
control headers.
.El
.El
.Ss Interrupts
While some hardware supports more than one interrupt queue, a single
interrupt is generally sufficient for most host controllers.
If the controller supports interrupt coalescing, then the driver should
generally enable it and set it to a moderate rate.
.Ss driver.conf considerations
Due to the way host controller drivers need to interact with hotplug,
drivers should generally set the
.Sy ddi-forceattach
property to one in their
.Xr driver.conf 4
file.
.Sh SEE ALSO
.Xr driver.conf 4 ,
.Xr hubd 7D ,
.Xr usba 7D ,
.Xr attach 9E ,
.Xr close 9E ,
.Xr detach 9E ,
.Xr getinfo 9E ,
.Xr ioctl 9E ,
.Xr open 9E ,
.Xr usba_hcdi_cb_close 9E ,
.Xr usba_hcdi_cb_ioctl 9E ,
.Xr usba_hcdi_cb_open 9E ,
.Xr usba_hcdi_pipe_bulk_xfer 9E ,
.Xr usba_hcdi_pipe_ctrl_xfer 9E ,
.Xr usba_hcdi_pipe_intr_xfer 9E ,
.Xr usba_hcdi_pipe_isoc_xfer 9E ,
.Xr usba_hcdi_pipe_open 9E ,
.Xr ddi_dma_addr_bind_handle 9F ,
.Xr ddi_get_driver_private 9F ,
.Xr ddi_prop_op 9F ,
.Xr desballoc 9F ,
.Xr nochpoll 9F ,
.Xr nodev 9F ,
.Xr timeout 9F ,
.Xr usba_alloc_hcdi_ops 9F ,
.Xr usba_hcdi_cb 9F ,
.Xr usba_hcdi_dup_intr_req 9F ,
.Xr usba_hcdi_dup_isoc_req 9F ,
.Xr usba_hcdi_register 9F ,
.Xr usba_hcdi_unregister 9F ,
.Xr usba_hubdi_bind_root_hub 9F ,
.Xr usba_hubdi_close 9F ,
.Xr usba_hubdi_dev_ops 9F ,
.Xr usba_hubdi_ioctl 9F ,
.Xr usba_hubdi_open 9F ,
.Xr usba_hubdi_unbind_root_hub 9F ,
.Xr cb_ops 9S ,
.Xr dev_ops 9S ,
.Xr mblk 9S ,
.Xr usb_bulk_req 9S ,
.Xr usb_cfg_descr 9S ,
.Xr usb_ctrl_req 9S ,
.Xr usb_dev_descr 9S ,
.Xr usb_ep_descr 9S ,
.Xr usb_ep_ss_comp_descr 9S ,
.Xr usb_if_descr 9S ,
.Xr usb_intr_req 9S ,
.Xr usb_isoc_req 9S ,
.Xr usba_hcdi_ops 9S