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Commit 82c7465b authored by Jerome Oufella's avatar Jerome Oufella Committed by Guenter Roeck
Browse files

hwmon: (sht15) add support for CRC validation 



The sht15 sensor allows validating exchanges to and from the device
using a crc8 function. An utility function to reverse a byte has also
been added.

Signed-off-by: default avatarJerome Oufella <jerome.oufella@savoirfairelinux.com>
Acked-by: default avatarJonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: default avatarGuenter Roeck <guenter.roeck@ericsson.com>
parent cc15c7eb

Documentation/hwmon/sht15

+8 −1
Original line number Diff line number Diff line
@@ -5,6 +5,7 @@ Authors: 
  * Wouter Horre

  * Jonathan Cameron

  * Vivien Didelot <vivien.didelot@savoirfairelinux.com>

  * Jerome Oufella <jerome.oufella@savoirfairelinux.com>



Supported chips:

  * Sensirion SHT10
@@ -44,11 +45,17 @@ measurement and decrease power consumption, while loosing on precision. 
Some options may be set directly in the sht15_platform_data structure

or via sysfs attributes.



Note: The regulator supply name is set to "vcc".

Notes:

  * The regulator supply name is set to "vcc".

  * If a CRC validation fails, a soft reset command is sent, which resets

    status register to its hardware default value, but the driver will try to

    restore the previous device configuration.



Platform data

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



* checksum:

  set it to true to enable CRC validation of the readings (default to false).

* no_otp_reload:

  flag to indicate not to reload from OTP (default to false).

* low_resolution:

drivers/hwmon/sht15.c

+173 −19
Original line number Diff line number Diff line
@@ -2,6 +2,7 @@ 
 * sht15.c - support for the SHT15 Temperature and Humidity Sensor

 *

 * Portions Copyright (c) 2010-2011 Savoir-faire Linux Inc.

 *          Jerome Oufella <jerome.oufella@savoirfairelinux.com>

 *          Vivien Didelot <vivien.didelot@savoirfairelinux.com>

 *

 * Copyright (c) 2009 Jonathan Cameron
@@ -78,6 +79,42 @@ static const struct sht15_temppair temppoints[] = { 
	{ 5000000, -40100 },

};



/* Table from CRC datasheet, section 2.4 */

static const u8 sht15_crc8_table[] = {

	0,	49,	98,	83,	196,	245,	166,	151,

	185,	136,	219,	234,	125,	76,	31,	46,

	67,	114,	33,	16,	135,	182,	229,	212,

	250,	203,	152,	169,	62,	15,	92,	109,

	134,	183,	228,	213,	66,	115,	32,	17,

	63,	14,	93,	108,	251,	202,	153,	168,

	197,	244,	167,	150,	1,	48,	99,	82,

	124,	77,	30,	47,	184,	137,	218,	235,

	61,	12,	95,	110,	249,	200,	155,	170,

	132,	181,	230,	215,	64,	113,	34,	19,

	126,	79,	28,	45,	186,	139,	216,	233,

	199,	246,	165,	148,	3,	50,	97,	80,

	187,	138,	217,	232,	127,	78,	29,	44,

	2,	51,	96,	81,	198,	247,	164,	149,

	248,	201,	154,	171,	60,	13,	94,	111,

	65,	112,	35,	18,	133,	180,	231,	214,

	122,	75,	24,	41,	190,	143,	220,	237,

	195,	242,	161,	144,	7,	54,	101,	84,

	57,	8,	91,	106,	253,	204,	159,	174,

	128,	177,	226,	211,	68,	117,	38,	23,

	252,	205,	158,	175,	56,	9,	90,	107,

	69,	116,	39,	22,	129,	176,	227,	210,

	191,	142,	221,	236,	123,	74,	25,	40,

	6,	55,	100,	85,	194,	243,	160,	145,

	71,	118,	37,	20,	131,	178,	225,	208,

	254,	207,	156,	173,	58,	11,	88,	105,

	4,	53,	102,	87,	192,	241,	162,	147,

	189,	140,	223,	238,	121,	72,	27,	42,

	193,	240,	163,	146,	5,	52,	103,	86,

	120,	73,	26,	43,	188,	141,	222,	239,

	130,	179,	224,	209,	70,	119,	36,	21,

	59,	10,	89,	104,	255,	206,	157,	172

};



/**

 * struct sht15_data - device instance specific data

 * @pdata:		platform data (gpio's etc).
@@ -86,6 +123,8 @@ static const struct sht15_temppair temppoints[] = { 
 * @val_temp:		last temperature value read from device.

 * @val_humid:		last humidity value read from device.

 * @val_status:		last status register value read from device.

 * @checksum_ok:	last value read from the device passed CRC validation.

 * @checksumming:	flag used to enable the data validation with CRC.

 * @state:		state identifying the action the driver is doing.

 * @measurements_valid:	are the current stored measures valid (start condition).

 * @status_valid:	is the current stored status valid (start condition).
@@ -112,6 +151,8 @@ struct sht15_data { 
	uint16_t			val_temp;

	uint16_t			val_humid;

	u8				val_status;

	bool				checksum_ok;

	bool				checksumming;

	enum sht15_state		state;

	bool				measurements_valid;

	bool				status_valid;
@@ -128,6 +169,40 @@ struct sht15_data { 
	atomic_t			interrupt_handled;

};



/**

 * sht15_reverse() - reverse a byte

 * @byte:    byte to reverse.

 */

static u8 sht15_reverse(u8 byte)

{

	u8 i, c;



	for (c = 0, i = 0; i < 8; i++)

		c |= (!!(byte & (1 << i))) << (7 - i);

	return c;

}



/**

 * sht15_crc8() - compute crc8

 * @data:	sht15 specific data.

 * @value:	sht15 retrieved data.

 *

 * This implements section 2 of the CRC datasheet.

 */

static u8 sht15_crc8(struct sht15_data *data,

		const u8 *value,

		int len)

{

	u8 crc = sht15_reverse(data->val_status & 0x0F);



	while (len--) {

		crc = sht15_crc8_table[*value ^ crc];

		value++;

	}



	return crc;

}



/**

 * sht15_connection_reset() - reset the comms interface

 * @data:	sht15 specific data
@@ -267,6 +342,26 @@ static int sht15_soft_reset(struct sht15_data *data) 
	return ret;

}



/**

 * sht15_ack() - send a ack

 * @data:	sht15 specific data.

 *

 * Each byte of data is acknowledged by pulling the data line

 * low for one clock pulse.

 */

static void sht15_ack(struct sht15_data *data)

{

	gpio_direction_output(data->pdata->gpio_data, 0);

	ndelay(SHT15_TSU);

	gpio_set_value(data->pdata->gpio_sck, 1);

	ndelay(SHT15_TSU);

	gpio_set_value(data->pdata->gpio_sck, 0);

	ndelay(SHT15_TSU);

	gpio_set_value(data->pdata->gpio_data, 1);



	gpio_direction_input(data->pdata->gpio_data);

}



/**

 * sht15_end_transmission() - notify device of end of transmission

 * @data:	device state.
@@ -338,6 +433,9 @@ static int sht15_update_status(struct sht15_data *data) 
{

	int ret = 0;

	u8 status;

	u8 previous_config;

	u8 dev_checksum = 0;

	u8 checksum_vals[2];

	int timeout = HZ;



	mutex_lock(&data->read_lock);
@@ -348,8 +446,40 @@ static int sht15_update_status(struct sht15_data *data) 
			goto error_ret;

		status = sht15_read_byte(data);



		if (data->checksumming) {

			sht15_ack(data);

			dev_checksum = sht15_reverse(sht15_read_byte(data));

			checksum_vals[0] = SHT15_READ_STATUS;

			checksum_vals[1] = status;

			data->checksum_ok = (sht15_crc8(data, checksum_vals, 2)

					== dev_checksum);

		}



		sht15_end_transmission(data);



		/*

		 * Perform checksum validation on the received data.

		 * Specification mentions that in case a checksum verification

		 * fails, a soft reset command must be sent to the device.

		 */

		if (data->checksumming && !data->checksum_ok) {

			previous_config = data->val_status & 0x07;

			ret = sht15_soft_reset(data);

			if (ret)

				goto error_ret;

			if (previous_config) {

				ret = sht15_send_status(data, previous_config);

				if (ret) {

					dev_err(data->dev,

						"CRC validation failed, unable "

						"to restore device settings\n");

					goto error_ret;

				}

			}

			ret = -EAGAIN;

			goto error_ret;

		}



		data->val_status = status;

		data->status_valid = true;

		data->last_status = jiffies;
@@ -372,6 +502,7 @@ static int sht15_measurement(struct sht15_data *data, 
			     int timeout_msecs)

{

	int ret;

	u8 previous_config;



	ret = sht15_send_cmd(data, command);

	if (ret)
@@ -395,6 +526,29 @@ static int sht15_measurement(struct sht15_data *data, 
		sht15_connection_reset(data);

		return -ETIME;

	}



	/*

	 *  Perform checksum validation on the received data.

	 *  Specification mentions that in case a checksum verification fails,

	 *  a soft reset command must be sent to the device.

	 */

	if (data->checksumming && !data->checksum_ok) {

		previous_config = data->val_status & 0x07;

		ret = sht15_soft_reset(data);

		if (ret)

			return ret;

		if (previous_config) {

			ret = sht15_send_status(data, previous_config);

			if (ret) {

				dev_err(data->dev,

					"CRC validation failed, unable "

					"to restore device settings\n");

				return ret;

			}

		}

		return -EAGAIN;

	}



	return 0;

}
@@ -635,28 +789,11 @@ static irqreturn_t sht15_interrupt_fired(int irq, void *d) 
	return IRQ_HANDLED;

}



/**

 * sht15_ack() - Send an ack to the device

 *

 * Each byte of data is acknowledged by pulling the data line

 * low for one clock pulse.

 */

static void sht15_ack(struct sht15_data *data)

{

	gpio_direction_output(data->pdata->gpio_data, 0);

	ndelay(SHT15_TSU);

	gpio_set_value(data->pdata->gpio_sck, 1);

	ndelay(SHT15_TSU);

	gpio_set_value(data->pdata->gpio_sck, 0);

	ndelay(SHT15_TSU);

	gpio_set_value(data->pdata->gpio_data, 1);



	gpio_direction_input(data->pdata->gpio_data);

}



static void sht15_bh_read_data(struct work_struct *work_s)

{

	uint16_t val = 0;

	u8 dev_checksum = 0;

	u8 checksum_vals[3];

	struct sht15_data *data

		= container_of(work_s, struct sht15_data,

			       read_work);
@@ -681,6 +818,21 @@ static void sht15_bh_read_data(struct work_struct *work_s) 
	sht15_ack(data);

	val |= sht15_read_byte(data);



	if (data->checksumming) {

		/*

		 * Ask the device for a checksum and read it back.

		 * Note: the device sends the checksum byte reversed.

		 */

		sht15_ack(data);

		dev_checksum = sht15_reverse(sht15_read_byte(data));

		checksum_vals[0] = (data->state == SHT15_READING_TEMP) ?

			SHT15_MEASURE_TEMP : SHT15_MEASURE_RH;

		checksum_vals[1] = (u8) (val >> 8);

		checksum_vals[2] = (u8) val;

		data->checksum_ok

			= (sht15_crc8(data, checksum_vals, 3) == dev_checksum);

	}



	/* Tell the device we are done */

	sht15_end_transmission(data);
@@ -754,6 +906,8 @@ static int __devinit sht15_probe(struct platform_device *pdev) 
	}

	data->pdata = pdev->dev.platform_data;

	data->supply_uV = data->pdata->supply_mv * 1000;

	if (data->pdata->checksum)

		data->checksumming = true;

	if (data->pdata->no_otp_reload)

		status |= SHT15_STATUS_NO_OTP_RELOAD;

	if (data->pdata->low_resolution)

include/linux/sht15.h

+2 −0
Original line number Diff line number Diff line
@@ -19,6 +19,7 @@ 
 * @gpio_sck:		no. of gpio to which the data clock is connected.

 * @supply_mv:		supply voltage in mv. Overridden by regulator if

 *			available.

 * @checksum:		flag to indicate the checksum should be validated.

 * @no_otp_reload:	flag to indicate no reload from OTP.

 * @low_resolution:	flag to indicate the temp/humidity resolution to use.

 */
@@ -26,6 +27,7 @@ struct sht15_platform_data { 
	int gpio_data;

	int gpio_sck;

	int supply_mv;

	bool checksum;

	bool no_otp_reload;

	bool low_resolution;

};