Hi,
I have a few documentation comments below...
On 05/26/2018 02:19 PM, Marcus Folkesson wrote:
> 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@xxxxxxxxx>
> ---
> 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..5ac806b14604
> --- /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@xxxxxxxxx>
> +
> +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 is exposed to userspace via /dev/ccidg*.
are exposed
> +
> +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 bytes header followed by an optional
with a 10-byte header
(or maybe that's a locale difference)
> +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 specifies which slot that is the receiver in the `bSlot` field
specify which slot is the receiver
> +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 filedescriptor is allowed to be open to the device at a time.
file descriptor
> +
> +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 is described below followed by an example.
are
> +
> +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 defines in ccid.h [2]_.
as defined
> +The default value is 0x00000000.
[snip]
HTH.
--
~Randy
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