resources.
Most Linux developers will not be able to use this API, since they have
-USB "host" hardware in a PC, workstation, or server. Linux users with
+USB ``host`` hardware in a PC, workstation, or server. Linux users with
embedded systems are more likely to have USB peripheral hardware. To
distinguish drivers running inside such hardware from the more familiar
Linux "USB device drivers", which are host side proxies for the real USB
A system running inside a USB peripheral normally has at least three
layers inside the kernel to handle USB protocol processing, and may have
-additional layers in user space code. The "gadget" API is used by the
+additional layers in user space code. The ``gadget`` API is used by the
middle layer to interact with the lowest level (which directly handles
hardware).
*Additional Layers*
Other layers may exist. These could include kernel layers, such as
network protocol stacks, as well as user mode applications building
- on standard POSIX system call APIs such as *open()*, *close()*,
- *read()* and *write()*. On newer systems, POSIX Async I/O calls may
+ on standard POSIX system call APIs such as ``open()``, ``close()``,
+ ``read()`` and ``write()``. On newer systems, POSIX Async I/O calls may
be an option. Such user mode code will not necessarily be subject to
the GNU General Public License (GPL).
OTG-capable systems will also need to include a standard Linux-USB host
-side stack, with *usbcore*, one or more *Host Controller Drivers*
+side stack, with ``usbcore``, one or more *Host Controller Drivers*
(HCDs), *USB Device Drivers* to support the OTG "Targeted Peripheral
List", and so forth. There will also be an *OTG Controller Driver*,
which is visible to gadget and device driver developers only indirectly.
Kernel Mode Gadget API
======================
-Gadget drivers declare themselves through a *struct
-usb_gadget_driver*, which is responsible for most parts of enumeration
-for a *struct usb_gadget*. The response to a set_configuration usually
-involves enabling one or more of the *struct usb_ep* objects exposed by
-the gadget, and submitting one or more *struct usb_request* buffers to
+Gadget drivers declare themselves through a struct
+:c:type:`usb_gadget_driver`, which is responsible for most parts of enumeration
+for a struct :c:type:`usb_gadget`. The response to a set_configuration usually
+involves enabling one or more of the struct :c:type:`usb_ep` objects exposed by
+the gadget, and submitting one or more struct :c:type:`usb_request` buffers to
transfer data. Understand those four data types, and their operations,
and you will understand how this API works.
- **Note**
+.. Note::
- This documentation was prepared using the standard Linux kernel
- ``docproc`` tool, which turns text and in-code comments into SGML
- DocBook and then into usable formats such as HTML or PDF. Other than
- the "Chapter 9" data types, most of the significant data types and
- functions are described here.
+ Other than the "Chapter 9" data types, most of the significant data
+ types and functions are described here.
- However, docproc does not understand all the C constructs that are
- used, so some relevant information is likely omitted from what you
+ However, some relevant information is likely omitted from what you
are reading. One example of such information is endpoint
autoconfiguration. You'll have to read the header file, and use
example source code (such as that for "Gadget Zero"), to fully
The part of the API implementing some basic driver capabilities is
specific to the version of the Linux kernel that's in use. The 2.6
- kernel includes a *driver model* framework that has no analogue on
- earlier kernels; so those parts of the gadget API are not fully
- portable. (They are implemented on 2.4 kernels, but in a different
- way.) The driver model state is another part of this API that is
+ and upper kernel versions include a *driver model* framework that has
+ no analogue on earlier kernels; so those parts of the gadget API are
+ not fully portable. (They are implemented on 2.4 kernels, but in a
+ different way.) The driver model state is another part of this API that is
ignored by the kerneldoc tools.
The core API does not expose every possible hardware feature, only the
1. Register a driver for the particular device side usb controller
hardware, such as the net2280 on PCI (USB 2.0), sa11x0 or pxa25x as
found in Linux PDAs, and so on. At this point the device is logically
- in the USB ch9 initial state ("attached"), drawing no power and not
+ in the USB ch9 initial state (``attached``), drawing no power and not
usable (since it does not yet support enumeration). Any host should
not see the device, since it's not activated the data line pullup
used by the host to detect a device, even if VBUS power is available.
2. Register a gadget driver that implements some higher level device
- function. That will then bind() to a usb_gadget, which activates the
- data line pullup sometime after detecting VBUS.
+ function. That will then bind() to a :c:type:`usb_gadget`, which activates
+ the data line pullup sometime after detecting VBUS.
3. The hardware driver can now start enumerating. The steps it handles
- are to accept USB power and set_address requests. Other steps are
+ are to accept USB ``power`` and ``set_address`` requests. Other steps are
handled by the gadget driver. If the gadget driver module is unloaded
before the host starts to enumerate, steps before step 7 are skipped.
-4. The gadget driver's setup() call returns usb descriptors, based both
+4. The gadget driver's ``setup()`` call returns usb descriptors, based both
on what the bus interface hardware provides and on the functionality
being implemented. That can involve alternate settings or
configurations, unless the hardware prevents such operation. For OTG
devices, each configuration descriptor includes an OTG descriptor.
5. The gadget driver handles the last step of enumeration, when the USB
- host issues a set_configuration call. It enables all endpoints used
+ host issues a ``set_configuration`` call. It enables all endpoints used
in that configuration, with all interfaces in their default settings.
That involves using a list of the hardware's endpoints, enabling each
endpoint according to its descriptor. It may also involve using
- :c:func:`usb_gadget_vbus_draw()` to let more power be drawn
- from VBUS, as allowed by that configuration. For OTG devices, setting
- a configuration may also involve reporting HNP capabilities through a
+ ``usb_gadget_vbus_draw`` to let more power be drawn from VBUS, as
+ allowed by that configuration. For OTG devices, setting a
+ configuration may also involve reporting HNP capabilities through a
user interface.
6. Do real work and perform data transfers, possibly involving changes
Note that the lifecycle above can be slightly different for OTG devices.
Other than providing an additional OTG descriptor in each configuration,
only the HNP-related differences are particularly visible to driver
-code. They involve reporting requirements during the SET_CONFIGURATION
+code. They involve reporting requirements during the ``SET_CONFIGURATION``
request, and the option to invoke HNP during some suspend callbacks.
-Also, SRP changes the semantics of :c:func:`usb_gadget_wakeup()`
-slightly.
+Also, SRP changes the semantics of ``usb_gadget_wakeup`` slightly.
USB 2.0 Chapter 9 Types and Constants
-------------------------------------
Gadget drivers rely on common USB structures and constants defined in
-the ``<linux/usb/ch9.h>`` header file, which is standard in Linux 2.6
-kernels. These are the same types and constants used by host side
+the :ref:`linux/usb/ch9.h <usb_chapter9>` header file, which is standard in
+Linux 2.6+ kernels. These are the same types and constants used by host side
drivers (and usbcore).
-.. kernel-doc:: include/linux/usb/ch9.h
- :internal:
-
Core Objects and Methods
------------------------
necessarily sharing a given configuration). There is however an optional
framework which makes it easier to reuse and combine functions.
-Devices using this framework provide a *struct usb_composite_driver*,
-which in turn provides one or more *struct usb_configuration*
-instances. Each such configuration includes at least one *struct
-usb_function*, which packages a user visible role such as "network
+Devices using this framework provide a struct :c:type:`usb_composite_driver`,
+which in turn provides one or more struct :c:type:`usb_configuration`
+instances. Each such configuration includes at least one struct
+:c:type:`usb_function`, which packages a user visible role such as "network
link" or "mass storage device". Management functions may also exist,
such as "Device Firmware Upgrade".
At this writing, a few of the current gadget drivers have been converted
to this framework. Near-term plans include converting all of them,
-except for "gadgetfs".
-
-.. kernel-doc:: drivers/usb/gadget/function/f_acm.c
- :export:
-
-.. kernel-doc:: drivers/usb/gadget/function/f_ecm.c
- :export:
-
-.. kernel-doc:: drivers/usb/gadget/function/f_subset.c
- :export:
-
-.. kernel-doc:: drivers/usb/gadget/function/f_obex.c
- :export:
-
-.. kernel-doc:: drivers/usb/gadget/function/f_serial.c
- :export:
+except for ``gadgetfs``.
Peripheral Controller Drivers
=============================
and 2.6; contact NetChip Technologies for development boards and product
information.
-Other hardware working in the "gadget" framework includes: Intel's PXA
+Other hardware working in the ``gadget`` framework includes: Intel's PXA
25x and IXP42x series processors (``pxa2xx_udc``), Toshiba TC86c001
"Goku-S" (``goku_udc``), Renesas SH7705/7727 (``sh_udc``), MediaQ 11xx
(``mq11xx_udc``), Hynix HMS30C7202 (``h7202_udc``), National 9303/4
In addition to *Gadget Zero* (used primarily for testing and development
with drivers for usb controller hardware), other gadget drivers exist.
-There's an *ethernet* gadget driver, which implements one of the most
+There's an ``ethernet`` gadget driver, which implements one of the most
useful *Communications Device Class* (CDC) models. One of the standards
for cable modem interoperability even specifies the use of this ethernet
model as one of two mandatory options. Gadgets using this code look to a
subset doesn't advertise itself as CDC Ethernet, to avoid creating
problems.)
-Support for Microsoft's *RNDIS* protocol has been contributed by
+Support for Microsoft's ``RNDIS`` protocol has been contributed by
Pengutronix and Auerswald GmbH. This is like CDC Ethernet, but it runs
on more slightly USB hardware (but less than the CDC subset). However,
its main claim to fame is being able to connect directly to recent
versions of Windows, using drivers that Microsoft bundles and supports,
making it much simpler to network with Windows.
-There is also support for user mode gadget drivers, using *gadgetfs*.
+There is also support for user mode gadget drivers, using ``gadgetfs``.
This provides a *User Mode API* that presents each endpoint as a single
-file descriptor. I/O is done using normal *read()* and *read()* calls.
+file descriptor. I/O is done using normal ``read()`` and ``read()`` calls.
Familiar tools like GDB and pthreads can be used to develop and debug
user mode drivers, so that once a robust controller driver is available
many applications for it won't require new kernel mode software. Linux
including a special *Mini-AB* jack and associated transceiver to support
*Dual-Role* operation: they can act either as a host, using the standard
Linux-USB host side driver stack, or as a peripheral, using this
-"gadget" framework. To do that, the system software relies on small
+``gadget`` framework. To do that, the system software relies on small
additions to those programming interfaces, and on a new internal
component (here called an "OTG Controller") affecting which driver stack
connects to the OTG port. In each role, the system can re-use the
existing pool of hardware-neutral drivers, layered on top of the
-controller driver interfaces (*usb_bus* or *usb_gadget*). Such drivers
-need at most minor changes, and most of the calls added to support OTG
-can also benefit non-OTG products.
+controller driver interfaces (:c:type:`usb_bus` or :c:type:`usb_gadget`).
+Such drivers need at most minor changes, and most of the calls added to
+support OTG can also benefit non-OTG products.
-- Gadget drivers test the *is_otg* flag, and use it to determine
+- Gadget drivers test the ``is_otg`` flag, and use it to determine
whether or not to include an OTG descriptor in each of their
configurations.
- Gadget drivers may need changes to support the two new OTG protocols,
- exposed in new gadget attributes such as *b_hnp_enable* flag. HNP
+ exposed in new gadget attributes such as ``b_hnp_enable`` flag. HNP
support should be reported through a user interface (two LEDs could
suffice), and is triggered in some cases when the host suspends the
peripheral. SRP support can be user-initiated just like remote
wakeup, probably by pressing the same button.
- On the host side, USB device drivers need to be taught to trigger HNP
- at appropriate moments, using :c:func:`usb_suspend_device()`.
- That also conserves battery power, which is useful even for non-OTG
+ at appropriate moments, using ``usb_suspend_device()``. That also
+ conserves battery power, which is useful even for non-OTG
configurations.
- Also on the host side, a driver must support the OTG "Targeted
Peripheral List". That's just a whitelist, used to reject peripherals
not supported with a given Linux OTG host. *This whitelist is
- product-specific; each product must modify ``otg_whitelist.h`` to
+ product-specific; each product must modify* ``otg_whitelist.h`` *to
match its interoperability specification.*
Non-OTG Linux hosts, like PCs and workstations, normally have some
been distributed, so driver bugs can't normally be fixed if they're
found after shipment.
-Additional changes are needed below those hardware-neutral *usb_bus*
-and *usb_gadget* driver interfaces; those aren't discussed here in any
+Additional changes are needed below those hardware-neutral :c:type:`usb_bus`
+and :c:type:`usb_gadget` driver interfaces; those aren't discussed here in any
detail. Those affect the hardware-specific code for each USB Host or
Peripheral controller, and how the HCD initializes (since OTG can be
active only on a single port). They also involve what may be called an
projects / GitHub / moto-9609 / android_kernel_motorola_exynos9610.git / commitdiff