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usb/hotplug.txt: convert to ReST and add to driver-api book

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This document describe some USB core features. Add it to the
driver-api book.

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 2017-04-05 10:23:08 -03:00 committed by Jonathan Corbet
parent 360a7b5f57
commit 76f650f077
2 changed files with 37 additions and 30 deletions
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66
Documentation/usb/hotplug.txt → Documentation/driver-api/usb/hotplug.rst
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@ -1,4 +1,9 @@
LINUX HOTPLUGGING
USB hotplugging
~~~~~~~~~~~~~~~
Linux Hotplugging
=================
In hotpluggable busses like USB (and Cardbus PCI), end-users plug devices
into the bus with power on. In most cases, users expect the devices to become
@ -30,11 +35,11 @@ Because some of those actions rely on information about drivers (metadata)
that is currently available only when the drivers are dynamically linked,
you get the best hotplugging when you configure a highly modular system.
Kernel Hotplug Helper (``/sbin/hotplug``)
=========================================
KERNEL HOTPLUG HELPER (/sbin/hotplug)
There is a kernel parameter: /proc/sys/kernel/hotplug, which normally
holds the pathname "/sbin/hotplug". That parameter names a program
There is a kernel parameter: ``/proc/sys/kernel/hotplug``, which normally
holds the pathname ``/sbin/hotplug``. That parameter names a program
which the kernel may invoke at various times.
The /sbin/hotplug program can be invoked by any subsystem as part of its
@ -51,26 +56,26 @@ Hotplug software and other resources is available at:
Mailing list information is also available at that site.
--------------------------------------------------------------------------
USB Policy Agent
================
USB POLICY AGENT
The USB subsystem currently invokes /sbin/hotplug when USB devices
The USB subsystem currently invokes ``/sbin/hotplug`` when USB devices
are added or removed from system. The invocation is done by the kernel
hub workqueue [hub_wq], or else as part of root hub initialization
(done by init, modprobe, kapmd, etc). Its single command line parameter
is the string "usb", and it passes these environment variables:
ACTION ... "add", "remove"
PRODUCT ... USB vendor, product, and version codes (hex)
TYPE ... device class codes (decimal)
INTERFACE ... interface 0 class codes (decimal)
========== ============================================
ACTION ``add``, ``remove``
PRODUCT USB vendor, product, and version codes (hex)
TYPE device class codes (decimal)
INTERFACE interface 0 class codes (decimal)
========== ============================================
If "usbdevfs" is configured, DEVICE and DEVFS are also passed. DEVICE is
the pathname of the device, and is useful for devices with multiple and/or
alternate interfaces that complicate driver selection. By design, USB
hotplugging is independent of "usbdevfs": you can do most essential parts
hotplugging is independent of ``usbdevfs``: you can do most essential parts
of USB device setup without using that filesystem, and without running a
user mode daemon to detect changes in system configuration.
@ -79,19 +84,20 @@ modules, and can invoke driver-specific setup scripts. The newest ones
leverage USB module-init-tools support. Later agents might unload drivers.
USB MODUTILS SUPPORT
USB Modutils Support
====================
Current versions of module-init-tools will create a "modules.usbmap" file
which contains the entries from each driver's MODULE_DEVICE_TABLE. Such
Current versions of module-init-tools will create a ``modules.usbmap`` file
which contains the entries from each driver's ``MODULE_DEVICE_TABLE``. Such
files can be used by various user mode policy agents to make sure all the
right driver modules get loaded, either at boot time or later.
See <linux/usb.h> for full information about such table entries; or look
See ``linux/usb.h`` for full information about such table entries; or look
at existing drivers. Each table entry describes one or more criteria to
be used when matching a driver to a device or class of devices. The
specific criteria are identified by bits set in "match_flags", paired
with field values. You can construct the criteria directly, or with
macros such as these, and use driver_info to store more information.
macros such as these, and use driver_info to store more information::
USB_DEVICE (vendorId, productId)
... matching devices with specified vendor and product ids
@ -103,7 +109,7 @@ macros such as these, and use driver_info to store more information.
... matching specified device class info
A short example, for a driver that supports several specific USB devices
and their quirks, might have a MODULE_DEVICE_TABLE like this:
and their quirks, might have a MODULE_DEVICE_TABLE like this::
static const struct usb_device_id mydriver_id_table[] = {
{ USB_DEVICE (0x9999, 0xaaaa), driver_info: QUIRK_X },
@ -116,10 +122,10 @@ and their quirks, might have a MODULE_DEVICE_TABLE like this:
Most USB device drivers should pass these tables to the USB subsystem as
well as to the module management subsystem. Not all, though: some driver
frameworks connect using interfaces layered over USB, and so they won't
need such a "struct usb_driver".
need such a struct :c:type:`usb_driver`.
Drivers that connect directly to the USB subsystem should be declared
something like this:
something like this::
static struct usb_driver mydriver = {
.name = "mydriver",
@ -138,11 +144,11 @@ something like this:
When the USB subsystem knows about a driver's device ID table, it's used when
choosing drivers to probe(). The thread doing new device processing checks
drivers' device ID entries from the MODULE_DEVICE_TABLE against interface and
device descriptors for the device. It will only call probe() if there is a
match, and the third argument to probe() will be the entry that matched.
If you don't provide an id_table for your driver, then your driver may get
probed for each new device; the third parameter to probe() will be null.
drivers' device ID entries from the ``MODULE_DEVICE_TABLE`` against interface
and device descriptors for the device. It will only call ``probe()`` if there
is a match, and the third argument to ``probe()`` will be the entry that
matched.
If you don't provide an ``id_table`` for your driver, then your driver may get
probed for each new device; the third parameter to ``probe()`` will be
``NULL``.

1
Documentation/driver-api/usb/index.rst
View File

@ -11,6 +11,7 @@ Linux USB API
callbacks
dma
power-management
hotplug
error-codes
writing_usb_driver
writing_musb_glue_layer