forked from luck/tmp_suning_uos_patched
gadget.rst: Enrich its ReST representation and add kernel-doc tag
The pandoc conversion is not perfect. Do handwork in order to: - add a title to this chapter; - use the proper warning and note markups; - use kernel-doc to include Kernel header and c files; - remove legacy notes with regards to DocBook; - some other minor adjustments to make it better to read in text mode and in html. Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com> Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This commit is contained in:
Mauro Carvalho Chehab
Jonathan Corbet
parent
9a3c8b3545
commit
e1cfb8cabe
|
|
@ -38,7 +38,7 @@ address a number of important problems, including:
|
|||
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
|
||||
|
|
@ -64,7 +64,7 @@ Structure of Gadget Drivers
|
|||
|
||||
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).
|
||||
|
||||
|
|
@ -143,13 +143,13 @@ In Linux, from the bottom up, these layers are:
|
|||
*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.
|
||||
|
|
@ -174,24 +174,20 @@ combined, to implement composite devices.
|
|||
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
|
||||
|
|
@ -199,10 +195,10 @@ and you will understand how this API works.
|
|||
|
||||
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
|
||||
|
|
@ -246,34 +242,34 @@ needs to handle some differences. Use the API like this:
|
|||
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
|
||||
|
|
@ -300,22 +296,18 @@ built by integrating reusable components.
|
|||
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
|
||||
------------------------
|
||||
|
||||
|
|
@ -347,10 +339,10 @@ multi-configuration devices (also more than one function, but not
|
|||
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".
|
||||
|
||||
|
|
@ -365,22 +357,7 @@ Composite Device Functions
|
|||
|
||||
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
|
||||
=============================
|
||||
|
|
@ -391,7 +368,7 @@ which supports USB 2.0 high speed and is based on PCI. This is the
|
|||
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
|
||||
|
|
@ -422,7 +399,7 @@ Gadget Drivers
|
|||
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
|
||||
|
|
@ -434,16 +411,16 @@ driver also implements a "good parts only" subset of CDC Ethernet. (That
|
|||
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
|
||||
|
|
@ -479,35 +456,35 @@ Systems need specialized hardware support to implement OTG, notably
|
|||
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
|
||||
|
|
@ -520,8 +497,8 @@ can also benefit non-OTG products.
|
|||
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
|
||||
|
|
|
|||
Loading…
Reference in New Issue
Block a user