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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: Jerome Oufella <jerome.oufella@savoirfairelinux.com> Acked-by: Jonathan Cameron <jic23@cam.ac.uk> Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.com>
This commit is contained in:
Jerome Oufella
Guenter Roeck
parent
cc15c7ebb4
commit
82c7465b4d
@ -5,6 +5,7 @@ Authors:
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* Wouter Horre
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* Jonathan Cameron
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* Vivien Didelot <vivien.didelot@savoirfairelinux.com>
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* Jerome Oufella <jerome.oufella@savoirfairelinux.com>
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Supported chips:
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* Sensirion SHT10
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@ -44,11 +45,17 @@ measurement and decrease power consumption, while loosing on precision.
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Some options may be set directly in the sht15_platform_data structure
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or via sysfs attributes.
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Note: The regulator supply name is set to "vcc".
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Notes:
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* The regulator supply name is set to "vcc".
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* If a CRC validation fails, a soft reset command is sent, which resets
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status register to its hardware default value, but the driver will try to
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restore the previous device configuration.
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Platform data
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-------------
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* checksum:
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set it to true to enable CRC validation of the readings (default to false).
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* no_otp_reload:
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flag to indicate not to reload from OTP (default to false).
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* low_resolution:
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@ -2,6 +2,7 @@
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* sht15.c - support for the SHT15 Temperature and Humidity Sensor
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*
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* Portions Copyright (c) 2010-2011 Savoir-faire Linux Inc.
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* Jerome Oufella <jerome.oufella@savoirfairelinux.com>
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* Vivien Didelot <vivien.didelot@savoirfairelinux.com>
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*
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* Copyright (c) 2009 Jonathan Cameron
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@ -78,6 +79,42 @@ static const struct sht15_temppair temppoints[] = {
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{ 5000000, -40100 },
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};
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/* Table from CRC datasheet, section 2.4 */
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static const u8 sht15_crc8_table[] = {
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0, 49, 98, 83, 196, 245, 166, 151,
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185, 136, 219, 234, 125, 76, 31, 46,
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67, 114, 33, 16, 135, 182, 229, 212,
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250, 203, 152, 169, 62, 15, 92, 109,
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134, 183, 228, 213, 66, 115, 32, 17,
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63, 14, 93, 108, 251, 202, 153, 168,
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197, 244, 167, 150, 1, 48, 99, 82,
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124, 77, 30, 47, 184, 137, 218, 235,
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61, 12, 95, 110, 249, 200, 155, 170,
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132, 181, 230, 215, 64, 113, 34, 19,
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126, 79, 28, 45, 186, 139, 216, 233,
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199, 246, 165, 148, 3, 50, 97, 80,
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187, 138, 217, 232, 127, 78, 29, 44,
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2, 51, 96, 81, 198, 247, 164, 149,
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248, 201, 154, 171, 60, 13, 94, 111,
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65, 112, 35, 18, 133, 180, 231, 214,
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122, 75, 24, 41, 190, 143, 220, 237,
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195, 242, 161, 144, 7, 54, 101, 84,
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57, 8, 91, 106, 253, 204, 159, 174,
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128, 177, 226, 211, 68, 117, 38, 23,
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252, 205, 158, 175, 56, 9, 90, 107,
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69, 116, 39, 22, 129, 176, 227, 210,
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191, 142, 221, 236, 123, 74, 25, 40,
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6, 55, 100, 85, 194, 243, 160, 145,
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71, 118, 37, 20, 131, 178, 225, 208,
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254, 207, 156, 173, 58, 11, 88, 105,
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4, 53, 102, 87, 192, 241, 162, 147,
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189, 140, 223, 238, 121, 72, 27, 42,
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193, 240, 163, 146, 5, 52, 103, 86,
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120, 73, 26, 43, 188, 141, 222, 239,
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130, 179, 224, 209, 70, 119, 36, 21,
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59, 10, 89, 104, 255, 206, 157, 172
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};
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/**
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* struct sht15_data - device instance specific data
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* @pdata: platform data (gpio's etc).
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@ -86,6 +123,8 @@ static const struct sht15_temppair temppoints[] = {
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* @val_temp: last temperature value read from device.
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* @val_humid: last humidity value read from device.
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* @val_status: last status register value read from device.
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* @checksum_ok: last value read from the device passed CRC validation.
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* @checksumming: flag used to enable the data validation with CRC.
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* @state: state identifying the action the driver is doing.
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* @measurements_valid: are the current stored measures valid (start condition).
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* @status_valid: is the current stored status valid (start condition).
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@ -112,6 +151,8 @@ struct sht15_data {
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uint16_t val_temp;
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uint16_t val_humid;
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u8 val_status;
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bool checksum_ok;
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bool checksumming;
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enum sht15_state state;
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bool measurements_valid;
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bool status_valid;
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@ -128,6 +169,40 @@ struct sht15_data {
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atomic_t interrupt_handled;
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};
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/**
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* sht15_reverse() - reverse a byte
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* @byte: byte to reverse.
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*/
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static u8 sht15_reverse(u8 byte)
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{
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u8 i, c;
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for (c = 0, i = 0; i < 8; i++)
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c |= (!!(byte & (1 << i))) << (7 - i);
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return c;
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}
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/**
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* sht15_crc8() - compute crc8
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* @data: sht15 specific data.
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* @value: sht15 retrieved data.
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*
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* This implements section 2 of the CRC datasheet.
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*/
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static u8 sht15_crc8(struct sht15_data *data,
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const u8 *value,
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int len)
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{
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u8 crc = sht15_reverse(data->val_status & 0x0F);
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while (len--) {
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crc = sht15_crc8_table[*value ^ crc];
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value++;
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}
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return crc;
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}
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/**
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* sht15_connection_reset() - reset the comms interface
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* @data: sht15 specific data
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@ -267,6 +342,26 @@ static int sht15_soft_reset(struct sht15_data *data)
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return ret;
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}
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/**
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* sht15_ack() - send a ack
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* @data: sht15 specific data.
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*
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* Each byte of data is acknowledged by pulling the data line
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* low for one clock pulse.
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*/
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static void sht15_ack(struct sht15_data *data)
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{
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gpio_direction_output(data->pdata->gpio_data, 0);
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ndelay(SHT15_TSU);
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gpio_set_value(data->pdata->gpio_sck, 1);
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ndelay(SHT15_TSU);
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gpio_set_value(data->pdata->gpio_sck, 0);
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ndelay(SHT15_TSU);
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gpio_set_value(data->pdata->gpio_data, 1);
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gpio_direction_input(data->pdata->gpio_data);
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}
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/**
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* sht15_end_transmission() - notify device of end of transmission
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* @data: device state.
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@ -338,6 +433,9 @@ static int sht15_update_status(struct sht15_data *data)
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{
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int ret = 0;
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u8 status;
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u8 previous_config;
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u8 dev_checksum = 0;
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u8 checksum_vals[2];
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int timeout = HZ;
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mutex_lock(&data->read_lock);
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@ -348,8 +446,40 @@ static int sht15_update_status(struct sht15_data *data)
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goto error_ret;
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status = sht15_read_byte(data);
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if (data->checksumming) {
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sht15_ack(data);
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dev_checksum = sht15_reverse(sht15_read_byte(data));
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checksum_vals[0] = SHT15_READ_STATUS;
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checksum_vals[1] = status;
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data->checksum_ok = (sht15_crc8(data, checksum_vals, 2)
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== dev_checksum);
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}
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sht15_end_transmission(data);
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/*
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* Perform checksum validation on the received data.
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* Specification mentions that in case a checksum verification
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* fails, a soft reset command must be sent to the device.
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*/
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if (data->checksumming && !data->checksum_ok) {
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previous_config = data->val_status & 0x07;
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ret = sht15_soft_reset(data);
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if (ret)
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goto error_ret;
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if (previous_config) {
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ret = sht15_send_status(data, previous_config);
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if (ret) {
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dev_err(data->dev,
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"CRC validation failed, unable "
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"to restore device settings\n");
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goto error_ret;
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}
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}
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ret = -EAGAIN;
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goto error_ret;
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}
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data->val_status = status;
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data->status_valid = true;
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data->last_status = jiffies;
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@ -372,6 +502,7 @@ static int sht15_measurement(struct sht15_data *data,
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int timeout_msecs)
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{
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int ret;
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u8 previous_config;
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ret = sht15_send_cmd(data, command);
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if (ret)
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@ -395,6 +526,29 @@ static int sht15_measurement(struct sht15_data *data,
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sht15_connection_reset(data);
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return -ETIME;
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}
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/*
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* Perform checksum validation on the received data.
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* Specification mentions that in case a checksum verification fails,
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* a soft reset command must be sent to the device.
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*/
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if (data->checksumming && !data->checksum_ok) {
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previous_config = data->val_status & 0x07;
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ret = sht15_soft_reset(data);
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if (ret)
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return ret;
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if (previous_config) {
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ret = sht15_send_status(data, previous_config);
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if (ret) {
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dev_err(data->dev,
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"CRC validation failed, unable "
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"to restore device settings\n");
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return ret;
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}
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}
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return -EAGAIN;
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}
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return 0;
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}
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@ -635,28 +789,11 @@ static irqreturn_t sht15_interrupt_fired(int irq, void *d)
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return IRQ_HANDLED;
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}
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/**
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* sht15_ack() - Send an ack to the device
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*
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* Each byte of data is acknowledged by pulling the data line
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* low for one clock pulse.
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*/
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static void sht15_ack(struct sht15_data *data)
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{
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gpio_direction_output(data->pdata->gpio_data, 0);
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ndelay(SHT15_TSU);
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gpio_set_value(data->pdata->gpio_sck, 1);
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ndelay(SHT15_TSU);
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gpio_set_value(data->pdata->gpio_sck, 0);
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ndelay(SHT15_TSU);
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gpio_set_value(data->pdata->gpio_data, 1);
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gpio_direction_input(data->pdata->gpio_data);
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}
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static void sht15_bh_read_data(struct work_struct *work_s)
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{
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uint16_t val = 0;
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u8 dev_checksum = 0;
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u8 checksum_vals[3];
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struct sht15_data *data
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= container_of(work_s, struct sht15_data,
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read_work);
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@ -681,6 +818,21 @@ static void sht15_bh_read_data(struct work_struct *work_s)
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sht15_ack(data);
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val |= sht15_read_byte(data);
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if (data->checksumming) {
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/*
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* Ask the device for a checksum and read it back.
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* Note: the device sends the checksum byte reversed.
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*/
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sht15_ack(data);
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dev_checksum = sht15_reverse(sht15_read_byte(data));
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checksum_vals[0] = (data->state == SHT15_READING_TEMP) ?
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SHT15_MEASURE_TEMP : SHT15_MEASURE_RH;
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checksum_vals[1] = (u8) (val >> 8);
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checksum_vals[2] = (u8) val;
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data->checksum_ok
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= (sht15_crc8(data, checksum_vals, 3) == dev_checksum);
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}
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/* Tell the device we are done */
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sht15_end_transmission(data);
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@ -754,6 +906,8 @@ static int __devinit sht15_probe(struct platform_device *pdev)
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}
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data->pdata = pdev->dev.platform_data;
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data->supply_uV = data->pdata->supply_mv * 1000;
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if (data->pdata->checksum)
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data->checksumming = true;
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if (data->pdata->no_otp_reload)
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status |= SHT15_STATUS_NO_OTP_RELOAD;
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if (data->pdata->low_resolution)
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@ -19,6 +19,7 @@
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* @gpio_sck: no. of gpio to which the data clock is connected.
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* @supply_mv: supply voltage in mv. Overridden by regulator if
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* available.
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* @checksum: flag to indicate the checksum should be validated.
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* @no_otp_reload: flag to indicate no reload from OTP.
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* @low_resolution: flag to indicate the temp/humidity resolution to use.
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*/
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@ -26,6 +27,7 @@ struct sht15_platform_data {
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int gpio_data;
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int gpio_sck;
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int supply_mv;
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bool checksum;
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bool no_otp_reload;
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bool low_resolution;
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};
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