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

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

Signed-off-by: Mauro Carvalho Chehab <[e-mail]>
Acked-by: Greg Kroah-Hartman <[e-mail]>
Signed-off-by: Jonathan Corbet <[e-mail]>

Documentation/driver-api/usb/index.rst

···
    callbacks
    dma
    power-management
+   hotplug
    error-codes
    writing_usb_driver
    writing_musb_glue_layer

Documentation/usb/hotplug.txt Documentation/driver-api/usb/hotplug.rst

···
-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
···
 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
···
 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.
 
···
 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
···
 	... 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 },
···
 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",
···
 
 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.
+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.
-
-
+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``.