[PATCH v3 2/3] Documentation: usb: add documentation for USB CCID Gadget Device

[Marcus Folkesson <marcus.folkesson@gmail.com>]

Add documentation to give a brief description on how to use the
CCID Gadget Device.
This includes a description for all attributes followed by an example on
how to setup the device with ConfigFS.

Signed-off-by: Marcus Folkesson <marcus.folkesson@gmail.com>
---

Notes:
    v3:
    	- correct the grammer (thanks Randy)
    v2:
    	- add the missing changelog text

 Documentation/usb/gadget_ccid.rst | 267 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 267 insertions(+)
 create mode 100644 Documentation/usb/gadget_ccid.rst

diff --git a/Documentation/usb/gadget_ccid.rst b/Documentation/usb/gadget_ccid.rst
new file mode 100644
index 000000000000..524fe9e6ac19
--- /dev/null
+++ b/Documentation/usb/gadget_ccid.rst
@@ -0,0 +1,267 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+============
+CCID Gadget
+============
+
+:Author: Marcus Folkesson <marcus.folkesson@gmail.com>
+
+Introduction
+============
+
+The CCID Gadget will present itself as a CCID device to the host system.
+The device supports two endpoints for now; BULK IN and BULK OUT.
+These endpoints are exposed to userspace via /dev/ccidg*.
+
+All CCID commands are sent on the BULK-OUT endpoint. Each command sent to the CCID
+has an associated ending response. Some commands can also have intermediate
+responses. The response is sent on the BULK-IN endpoint.
+See Figure 3-3 in the CCID Specification [1]_ for more details.
+
+The CCID commands must be handled in userspace since the driver is only working
+as a transport layer for the TPDUs.
+
+
+CCID Commands
+--------------
+
+All CCID commands begins with a 10-byte header followed by an optional
+data field depending on message type.
+
++--------+--------------+-------+----------------------------------+
+| Offset | Field        | Size  | Description                      |
++========+==============+=======+==================================+
+| 0      | bMessageType | 1     | Type of message                  |
++--------+--------------+-------+----------------------------------+
+| 1      | dwLength     | 4     | Message specific data length     |
+|        |              |       |                                  |
++--------+--------------+-------+----------------------------------+
+| 5      | bSlot        | 1     | Identifies the slot number       |
+|        |              |       | for this command                 |
++--------+--------------+-------+----------------------------------+
+| 6      | bSeq         | 1     | Sequence number for command      |
++--------+--------------+-------+----------------------------------+
+| 7      | ...          | 3     | Fields depends on message type   |
++--------+--------------+-------+----------------------------------+
+| 10     | abData       | array | Message specific data (OPTIONAL) |
++--------+--------------+-------+----------------------------------+
+
+
+Multiple CCID gadgets
+----------------------
+
+It is possible to create multiple instances of the CCID gadget, however,
+a much more flexible way is to create one gadget and set the `nslots` attribute
+to the number of desired CCID devices.
+
+All CCID commands specify which slot is the receiver in the `bSlot` field
+of the CCID header.
+
+Usage
+=====
+
+Access from userspace
+----------------------
+All communication is by read(2) and write(2) to the corresponding /dev/ccidg* device.
+Only one file descriptor is allowed to be open to the device at a time.
+
+The buffer size provided to read(2) **must be at least** 522 (10 bytes header + 512 bytes payload)
+bytes as we are working with whole commands.
+
+The buffer size provided to write(2) **may not exceed** 522 (10 bytes header + 512 bytes payload)
+bytes as we are working with whole commands.
+
+
+Configuration with configfs
+----------------------------
+
+ConfigFS is used to create and configure the CCID gadget.
+In order to get a device to work as intended, a few attributes must
+be considered.
+
+The attributes are described below followed by an example.
+
+features
+~~~~~~~~~
+
+The `feature` attribute writes to the dwFeatures field in the class descriptor.
+See Table 5.1-1 Smart Card Device Descriptors in the CCID Specification [1]_.
+
+The value indicates what intelligent features the CCID has.
+These values are available to user application as defined in ccid.h [2]_.
+The default value is 0x00000000.
+
+The value is a bitwise OR operation performed on the following values:
+
++------------+----------------------------------------------------------------+
+| Value      | Description                                                    |
++============+================================================================+
+| 0x00000000 | No special characteristics                                     |
++------------+----------------------------------------------------------------+
+| 0x00000002 | Automatic parameter configuration based on ATR data            |
++------------+----------------------------------------------------------------+
+| 0x00000004 | Automatic activation of ICC on inserting                       |
++------------+----------------------------------------------------------------+
+| 0x00000008 | Automatic ICC voltage selection                                |
++------------+----------------------------------------------------------------+
+| 0x00000010 | Automatic ICC clock frequency change according to active       |
+|            | parameters provided by the Host or self determined             |
++------------+----------------------------------------------------------------+
+| 0x00000020 | Automatic baud rate change according to active                 |
+|            | parameters provided by the Host or self determined             |
++------------+----------------------------------------------------------------+
+| 0x00000040 | Automatic parameters negotiation made by the CCID              |
++------------+----------------------------------------------------------------+
+| 0x00000080 | Automatic PPS made by the CCID according to the                |
+|            | active parameters                                              |
++------------+----------------------------------------------------------------+
+| 0x00000100 | CCID can set ICC in clock stop mode                            |
++------------+----------------------------------------------------------------+
+| 0x00000200 | NAD value other than 00 accepted (T=1 protocol in use)         |
++------------+----------------------------------------------------------------+
+| 0x00000400 | Automatic IFSD exchange as first exchange                      |
++------------+----------------------------------------------------------------+
+
+
+Only one of the following values may be present to select a level of exchange:
+
++------------+--------------------------------------------------+
+| Value      | Description                                      |
++============+==================================================+
+| 0x00010000 | TPDU level exchanges with CCID                   |
++------------+--------------------------------------------------+
+| 0x00020000 | Short APDU level exchange with CCID              |
++------------+--------------------------------------------------+
+| 0x00040000 | Short and Extended APDU level exchange with CCID |
++------------+--------------------------------------------------+
+
+If none of those values is indicated the level of exchange is
+character.
+
+
+protocols
+~~~~~~~~~~
+The `protocols` attribute writes to the dwProtocols field in the class descriptor.
+See Table 5.1-1 Smart Card Device Descriptors in the CCID Specification [1]_.
+
+The value is a bitwise OR operation performed on the following values:
+
++--------+--------------+
+| Value  | Description  |
++========+==============+
+| 0x0001 | Protocol T=0 |
++--------+--------------+
+| 0x0002 | Protocol T=1 |
++--------+--------------+
+
+If no protocol is selected both T=0 and T=1 will be supported (`protocols` = 0x0003).
+
+nslots
+~~~~~~
+
+The `nslots` attribute writes to the bMaxSlotIndex field in the class descriptor.
+See Table 5.1-1 Smart Card Device Descriptors in the CCID Specification [1]_.
+
+This is the index of the highest available slot on this device. All slots are consecutive starting at 00h.
+i.e. 0Fh = 16 slots on this device numbered 00h to 0Fh.
+
+The default value is 0, which means one slot.
+
+
+pinsupport
+~~~~~~~~~~~~
+
+This value indicates what PIN support features the CCID has.
+
+The `pinsupport` attribute writes to the dwPINSupport field in the class descriptor.
+See Table 5.1-1 Smart Card Device Descriptors in the CCID Specification [1]_.
+
+
+The value is a bitwise OR operation performed on the following values:
+
++--------+----------------------------+
+| Value  | Description                |
++========+============================+
+| 0x00   | No PIN support             |
++--------+----------------------------+
+| 0x01   | PIN Verification supported |
++--------+----------------------------+
+| 0x02   | PIN Modification supported |
++--------+----------------------------+
+
+The default value is set to 0x00.
+
+
+lcdlayout
+~~~~~~~~~~
+
+Number of lines and characters for the LCD display used to send messages for PIN entry.
+
+The `lcdLayout` attribute writes to the wLcdLayout field in the class descriptor.
+See Table 5.1-1 Smart Card Device Descriptors in the CCID Specification [1]_.
+
+
+The value is set as follows:
+
++--------+------------------------------------+
+| Value  | Description                        |
++========+====================================+
+| 0x0000 | No LCD                             |
++--------+------------------------------------+
+| 0xXXYY | XX: number of lines                |
+|        | YY: number of characters per line. |
++--------+------------------------------------+
+
+The default value is set to 0x0000.
+
+
+Example
+-------
+
+Here is an example on how to setup a CCID gadget with configfs ::
+
+    #!/bin/sh
+
+    CONFIGDIR=/sys/kernel/config
+    GADGET=$CONFIGDIR/usb_gadget/g0
+    FUNCTION=$GADGET/functions/ccid.sc0
+
+    VID=YOUR_VENDOR_ID_HERE
+    PID=YOUR_PRODUCT_ID_HERE
+    UDC=YOUR_UDC_HERE
+
+    #Mount filesystem
+    mount none -t configfs $CONFIGDIR
+
+    #Populate ID:s
+    echo $VID > $GADGET/idVendor
+    echo $PID > $GADGET/idProduct
+
+    #Create and configure the gadget
+    mkdir $FUNCTION
+    echo 0x000407B8 > $FUNCTION/features
+    echo 0x02 > $FUNCTION/protocols
+
+    #Create our english strings
+    mkdir  $GADGET/strings/0x409
+    echo 556677 > $GADGET/strings/0x409/serialnumber
+    echo "Hungry Penguins" > $GADGET/strings/0x409/manufacturer
+    echo "Harpoon With SmartCard"  > $GADGET/strings/0x409/product
+
+    #Create configuration
+    mkdir  $GADGET/configs/c.1
+    mkdir  $GADGET/configs/c.1/strings/0x409
+    echo Config1 > $GADGET/configs/c.1/strings/0x409/configuration
+
+    #Use `Config1` for our CCID gadget
+    ln -s $FUNCTION $GADGET/configs/c.1
+
+    #Execute
+    echo $UDC > $GADGET/UDC
+
+
+References
+==========
+
+.. [1] http://www.usb.org/developers/docs/devclass_docs/DWG_Smart-Card_CCID_Rev110.pdf
+.. [2] include/uapi/linux/usb/ccid.h
-- 
2.16.2

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