NFC: Update pn544 documentation

Kernel driver for the NXP Semiconductors PN544 Near Field

Communication chip

Author: Jari Vanhala

Contact: Matti Aaltonen (matti.j.aaltonen at nokia.com)

General

-------

The PN544 is an integrated transmission module for contactless

communication. The driver goes under drives/nfc/ and is compiled as a

module named "pn544". It registers a misc device and creates a device

file named "/dev/pn544".

module named "pn544".

Host Interfaces: I2C, SPI and HSU, this driver supports currently only I2C.

The Interface

-------------

The driver offers a sysfs interface for a hardware test and an IOCTL

interface for selecting between two operating modes. There are read,

write and poll functions for transferring messages. The two operating

modes are the normal (HCI) mode and the firmware update mode.

PN544 is controlled by sending messages from the userspace to the

chip. The main function of the driver is just to pass those messages

without caring about the message content.

Protocols

---------

For the ETSI HCI specification see

http://www.etsi.org/WebSite/Technologies/ProtocolSpecification.aspx

The Hardware Test

-----------------

The idea of the test is that it can performed by reading from the

corresponding sysfs file. The test is implemented in the board file

and it should test that PN544 can be put into the firmware update

mode. If the test is not implemented the sysfs file does not get

created.

Example:

> cat /sys/module/pn544/drivers/i2c\:pn544/3-002b/nfc_test

1

Normal Operation

----------------

PN544 is powered up when the device file is opened, otherwise it's

turned off. Only one instance can use the device at a time.

Userspace applications control PN544 with HCI messages. The hardware

sends an interrupt when data is available for reading. Data is

physically read when the read function is called by a userspace

application. Poll() checks the read interrupt state. Configuration and

self testing are also done from the userspace using read and write.

Example platform data:

static int rx71_pn544_nfc_request_resources(struct i2c_client *client)

{

	/* Get and setup the HW resources for the device */

}

static void rx71_pn544_nfc_free_resources(void)

{

	/* Release the HW resources */

}

static void rx71_pn544_nfc_enable(int fw)

{

	/* Turn the device on */

}

static int rx71_pn544_nfc_test(void)

{

	/*

	 * Put the device into the FW update mode

	 * and then back to the normal mode.

	 * Check the behavior and return one on success,

	 * zero on failure.

	 */

}

static void rx71_pn544_nfc_disable(void)

{

	/* turn the power off */

}

static struct pn544_nfc_platform_data rx71_nfc_data = {

	.request_resources = rx71_pn544_nfc_request_resources,

	.free_resources = rx71_pn544_nfc_free_resources,

	.enable = rx71_pn544_nfc_enable,

	.test = rx71_pn544_nfc_test,

	.disable = rx71_pn544_nfc_disable,

};