hwmon: (pcf8591) Don't attempt to detect devices

Supported chips:

  * Philips/NXP PCF8591

    Prefix: 'pcf8591'

    Addresses scanned: I2C 0x48 - 0x4f

    Addresses scanned: none

    Datasheet: Publicly available at the NXP website

               http://www.nxp.com/pip/PCF8591_6.html

Accessing PCF8591 via /sys interface

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

! Be careful !

The PCF8591 is plainly impossible to detect! Stupid chip.

So every chip with address in the interval [0x48..0x4f] is

detected as PCF8591. If you have other chips in this address

range, the workaround is to load this module after the one

for your others chips.

The PCF8591 is plainly impossible to detect! Thus the driver won't even

try. You have to explicitly instantiate the device at the relevant

address (in the interval [0x48..0x4f]) either through platform data, or

using the sysfs interface. See Documentation/i2c/instantiating-devices

for details.

On detection (i.e. insmod, modprobe et al.), directories are being

created for each detected PCF8591:

Directories are being created for each instantiated PCF8591:

/sys/bus/i2c/devices/<0>-<1>/

where <0> is the bus the chip was detected on (e. g. i2c-0)

where <0> is the bus the chip is connected to (e. g. i2c-0)

and <1> the chip address ([48..4f])

Inside these directories, there are such files:

#include <linux/err.h>

#include <linux/hwmon.h>

/* Addresses to scan */

static const unsigned short normal_i2c[] = { 0x48, 0x49, 0x4a, 0x4b, 0x4c,

					0x4d, 0x4e, 0x4f, I2C_CLIENT_END };

/* Insmod parameters */

static int input_mode;

 * Real code

 */

/* Return 0 if detection is successful, -ENODEV otherwise */

static int pcf8591_detect(struct i2c_client *client,

			  struct i2c_board_info *info)

{

	struct i2c_adapter *adapter = client->adapter;

	if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_BYTE

				     | I2C_FUNC_SMBUS_WRITE_BYTE_DATA))

		return -ENODEV;

	/* Now, we would do the remaining detection. But the PCF8591 is plainly

	   impossible to detect! Stupid chip. */

	strlcpy(info->type, "pcf8591", I2C_NAME_SIZE);

	return 0;

}

static int pcf8591_probe(struct i2c_client *client,

			 const struct i2c_device_id *id)

{

	.probe		= pcf8591_probe,

	.remove		= pcf8591_remove,

	.id_table	= pcf8591_id,

	.class		= I2C_CLASS_HWMON,	/* Nearest choice */

	.detect		= pcf8591_detect,

	.address_list	= normal_i2c,

};

static int __init pcf8591_init(void)