mirror of
https://github.com/edk2-porting/linux-next.git
synced 2024-12-22 20:23:57 +08:00
720a8d369b
Signed-off-by: Frans Klaver <frans.klaver@xsens.com> Signed-off-by: Jiri Kosina <jkosina@suse.cz>
385 lines
10 KiB
Plaintext
385 lines
10 KiB
Plaintext
|
|
|
|
|
|
|
|
Linux USB gadget configured through configfs
|
|
|
|
|
|
25th April 2013
|
|
|
|
|
|
|
|
|
|
Overview
|
|
========
|
|
|
|
A USB Linux Gadget is a device which has a UDC (USB Device Controller) and can
|
|
be connected to a USB Host to extend it with additional functions like a serial
|
|
port or a mass storage capability.
|
|
|
|
A gadget is seen by its host as a set of configurations, each of which contains
|
|
a number of interfaces which, from the gadget's perspective, are known as
|
|
functions, each function representing e.g. a serial connection or a SCSI disk.
|
|
|
|
Linux provides a number of functions for gadgets to use.
|
|
|
|
Creating a gadget means deciding what configurations there will be
|
|
and which functions each configuration will provide.
|
|
|
|
Configfs (please see Documentation/filesystems/configfs/*) lends itself nicely
|
|
for the purpose of telling the kernel about the above mentioned decision.
|
|
This document is about how to do it.
|
|
|
|
It also describes how configfs integration into gadget is designed.
|
|
|
|
|
|
|
|
|
|
Requirements
|
|
============
|
|
|
|
In order for this to work configfs must be available, so CONFIGFS_FS must be
|
|
'y' or 'm' in .config. As of this writing USB_LIBCOMPOSITE selects CONFIGFS_FS.
|
|
|
|
|
|
|
|
|
|
Usage
|
|
=====
|
|
|
|
(The original post describing the first function
|
|
made available through configfs can be seen here:
|
|
http://www.spinics.net/lists/linux-usb/msg76388.html)
|
|
|
|
$ modprobe libcomposite
|
|
$ mount none $CONFIGFS_HOME -t configfs
|
|
|
|
where CONFIGFS_HOME is the mount point for configfs
|
|
|
|
1. Creating the gadgets
|
|
-----------------------
|
|
|
|
For each gadget to be created its corresponding directory must be created:
|
|
|
|
$ mkdir $CONFIGFS_HOME/usb_gadget/<gadget name>
|
|
|
|
e.g.:
|
|
|
|
$ mkdir $CONFIGFS_HOME/usb_gadget/g1
|
|
|
|
...
|
|
...
|
|
...
|
|
|
|
$ cd $CONFIGFS_HOME/usb_gadget/g1
|
|
|
|
Each gadget needs to have its vendor id <VID> and product id <PID> specified:
|
|
|
|
$ echo <VID> > idVendor
|
|
$ echo <PID> > idProduct
|
|
|
|
A gadget also needs its serial number, manufacturer and product strings.
|
|
In order to have a place to store them, a strings subdirectory must be created
|
|
for each language, e.g.:
|
|
|
|
$ mkdir strings/0x409
|
|
|
|
Then the strings can be specified:
|
|
|
|
$ echo <serial number> > strings/0x409/serialnumber
|
|
$ echo <manufacturer> > strings/0x409/manufacturer
|
|
$ echo <product> > strings/0x409/product
|
|
|
|
2. Creating the configurations
|
|
------------------------------
|
|
|
|
Each gadget will consist of a number of configurations, their corresponding
|
|
directories must be created:
|
|
|
|
$ mkdir configs/<name>.<number>
|
|
|
|
where <name> can be any string which is legal in a filesystem and the
|
|
<number> is the configuration's number, e.g.:
|
|
|
|
$ mkdir configs/c.1
|
|
|
|
...
|
|
...
|
|
...
|
|
|
|
Each configuration also needs its strings, so a subdirectory must be created
|
|
for each language, e.g.:
|
|
|
|
$ mkdir configs/c.1/strings/0x409
|
|
|
|
Then the configuration string can be specified:
|
|
|
|
$ echo <configuration> > configs/c.1/strings/0x409/configuration
|
|
|
|
Some attributes can also be set for a configuration, e.g.:
|
|
|
|
$ echo 120 > configs/c.1/MaxPower
|
|
|
|
3. Creating the functions
|
|
-------------------------
|
|
|
|
The gadget will provide some functions, for each function its corresponding
|
|
directory must be created:
|
|
|
|
$ mkdir functions/<name>.<instance name>
|
|
|
|
where <name> corresponds to one of allowed function names and instance name
|
|
is an arbitrary string allowed in a filesystem, e.g.:
|
|
|
|
$ mkdir functions/ncm.usb0 # usb_f_ncm.ko gets loaded with request_module()
|
|
|
|
...
|
|
...
|
|
...
|
|
|
|
Each function provides its specific set of attributes, with either read-only
|
|
or read-write access. Where applicable they need to be written to as
|
|
appropriate.
|
|
Please refer to Documentation/ABI/*/configfs-usb-gadget* for more information.
|
|
|
|
4. Associating the functions with their configurations
|
|
------------------------------------------------------
|
|
|
|
At this moment a number of gadgets is created, each of which has a number of
|
|
configurations specified and a number of functions available. What remains
|
|
is specifying which function is available in which configuration (the same
|
|
function can be used in multiple configurations). This is achieved with
|
|
creating symbolic links:
|
|
|
|
$ ln -s functions/<name>.<instance name> configs/<name>.<number>
|
|
|
|
e.g.:
|
|
|
|
$ ln -s functions/ncm.usb0 configs/c.1
|
|
|
|
...
|
|
...
|
|
...
|
|
|
|
5. Enabling the gadget
|
|
----------------------
|
|
|
|
All the above steps serve the purpose of composing the gadget of
|
|
configurations and functions.
|
|
|
|
An example directory structure might look like this:
|
|
|
|
.
|
|
./strings
|
|
./strings/0x409
|
|
./strings/0x409/serialnumber
|
|
./strings/0x409/product
|
|
./strings/0x409/manufacturer
|
|
./configs
|
|
./configs/c.1
|
|
./configs/c.1/ncm.usb0 -> ../../../../usb_gadget/g1/functions/ncm.usb0
|
|
./configs/c.1/strings
|
|
./configs/c.1/strings/0x409
|
|
./configs/c.1/strings/0x409/configuration
|
|
./configs/c.1/bmAttributes
|
|
./configs/c.1/MaxPower
|
|
./functions
|
|
./functions/ncm.usb0
|
|
./functions/ncm.usb0/ifname
|
|
./functions/ncm.usb0/qmult
|
|
./functions/ncm.usb0/host_addr
|
|
./functions/ncm.usb0/dev_addr
|
|
./UDC
|
|
./bcdUSB
|
|
./bcdDevice
|
|
./idProduct
|
|
./idVendor
|
|
./bMaxPacketSize0
|
|
./bDeviceProtocol
|
|
./bDeviceSubClass
|
|
./bDeviceClass
|
|
|
|
|
|
Such a gadget must be finally enabled so that the USB host can enumerate it.
|
|
In order to enable the gadget it must be bound to a UDC (USB Device Controller).
|
|
|
|
$ echo <udc name> > UDC
|
|
|
|
where <udc name> is one of those found in /sys/class/udc/*
|
|
e.g.:
|
|
|
|
$ echo s3c-hsotg > UDC
|
|
|
|
|
|
6. Disabling the gadget
|
|
-----------------------
|
|
|
|
$ echo "" > UDC
|
|
|
|
7. Cleaning up
|
|
--------------
|
|
|
|
Remove functions from configurations:
|
|
|
|
$ rm configs/<config name>.<number>/<function>
|
|
|
|
where <config name>.<number> specify the configuration and <function> is
|
|
a symlink to a function being removed from the configuration, e.g.:
|
|
|
|
$ rm configfs/c.1/ncm.usb0
|
|
|
|
...
|
|
...
|
|
...
|
|
|
|
Remove strings directories in configurations
|
|
|
|
$ rmdir configs/<config name>.<number>/strings/<lang>
|
|
|
|
e.g.:
|
|
|
|
$ rmdir configs/c.1/strings/0x409
|
|
|
|
...
|
|
...
|
|
...
|
|
|
|
and remove the configurations
|
|
|
|
$ rmdir configs/<config name>.<number>
|
|
|
|
e.g.:
|
|
|
|
rmdir configs/c.1
|
|
|
|
...
|
|
...
|
|
...
|
|
|
|
Remove functions (function modules are not unloaded, though)
|
|
|
|
$ rmdir functions/<name>.<instance name>
|
|
|
|
e.g.:
|
|
|
|
$ rmdir functions/ncm.usb0
|
|
|
|
...
|
|
...
|
|
...
|
|
|
|
Remove strings directories in the gadget
|
|
|
|
$ rmdir strings/<lang>
|
|
|
|
e.g.:
|
|
|
|
$ rmdir strings/0x409
|
|
|
|
and finally remove the gadget:
|
|
|
|
$ cd ..
|
|
$ rmdir <gadget name>
|
|
|
|
e.g.:
|
|
|
|
$ rmdir g1
|
|
|
|
|
|
|
|
|
|
Implementation design
|
|
=====================
|
|
|
|
Below the idea of how configfs works is presented.
|
|
In configfs there are items and groups, both represented as directories.
|
|
The difference between an item and a group is that a group can contain
|
|
other groups. In the picture below only an item is shown.
|
|
Both items and groups can have attributes, which are represented as files.
|
|
The user can create and remove directories, but cannot remove files,
|
|
which can be read-only or read-write, depending on what they represent.
|
|
|
|
The filesystem part of configfs operates on config_items/groups and
|
|
configfs_attributes which are generic and of the same type for all
|
|
configured elements. However, they are embedded in usage-specific
|
|
larger structures. In the picture below there is a "cs" which contains
|
|
a config_item and an "sa" which contains a configfs_attribute.
|
|
|
|
The filesystem view would be like this:
|
|
|
|
./
|
|
./cs (directory)
|
|
|
|
|
+--sa (file)
|
|
|
|
|
.
|
|
.
|
|
.
|
|
|
|
Whenever a user reads/writes the "sa" file, a function is called
|
|
which accepts a struct config_item and a struct configfs_attribute.
|
|
In the said function the "cs" and "sa" are retrieved using the well
|
|
known container_of technique and an appropriate sa's function (show or
|
|
store) is called and passed the "cs" and a character buffer. The "show"
|
|
is for displaying the file's contents (copy data from the cs to the
|
|
buffer), while the "store" is for modifying the file's contents (copy data
|
|
from the buffer to the cs), but it is up to the implementer of the
|
|
two functions to decide what they actually do.
|
|
|
|
typedef struct configured_structure cs;
|
|
typedef struct specific_attribute sa;
|
|
|
|
sa
|
|
+----------------------------------+
|
|
cs | (*show)(cs *, buffer); |
|
|
+-----------------+ | (*store)(cs *, buffer, length); |
|
|
| | | |
|
|
| +-------------+ | | +------------------+ |
|
|
| | struct |-|----|------>|struct | |
|
|
| | config_item | | | |configfs_attribute| |
|
|
| +-------------+ | | +------------------+ |
|
|
| | +----------------------------------+
|
|
| data to be set | .
|
|
| | .
|
|
+-----------------+ .
|
|
|
|
The file names are decided by the config item/group designer, while
|
|
the directories in general can be named at will. A group can have
|
|
a number of its default sub-groups created automatically.
|
|
|
|
For more information on configfs please see
|
|
Documentation/filesystems/configfs/*.
|
|
|
|
The concepts described above translate to USB gadgets like this:
|
|
|
|
1. A gadget has its config group, which has some attributes (idVendor,
|
|
idProduct etc) and default sub-groups (configs, functions, strings).
|
|
Writing to the attributes causes the information to be stored in
|
|
appropriate locations. In the configs, functions and strings sub-groups
|
|
a user can create their sub-groups to represent configurations, functions,
|
|
and groups of strings in a given language.
|
|
|
|
2. The user creates configurations and functions, in the configurations
|
|
creates symbolic links to functions. This information is used when the
|
|
gadget's UDC attribute is written to, which means binding the gadget
|
|
to the UDC. The code in drivers/usb/gadget/configfs.c iterates over
|
|
all configurations, and in each configuration it iterates over all
|
|
functions and binds them. This way the whole gadget is bound.
|
|
|
|
3. The file drivers/usb/gadget/configfs.c contains code for
|
|
|
|
- gadget's config_group
|
|
- gadget's default groups (configs, functions, strings)
|
|
- associating functions with configurations (symlinks)
|
|
|
|
4. Each USB function naturally has its own view of what it wants
|
|
configured, so config_groups for particular functions are defined
|
|
in the functions implementation files drivers/usb/gadget/f_*.c.
|
|
|
|
5. Function's code is written in such a way that it uses
|
|
|
|
usb_get_function_instance(), which, in turn, calls request_module.
|
|
So, provided that modprobe works, modules for particular functions
|
|
are loaded automatically. Please note that the converse is not true:
|
|
after a gadget is disabled and torn down, the modules remain loaded.
|