diff options
Diffstat (limited to 'drivers/hwmon/sht15.c')
| -rw-r--r-- | drivers/hwmon/sht15.c | 192 |
1 files changed, 173 insertions, 19 deletions
diff --git a/drivers/hwmon/sht15.c b/drivers/hwmon/sht15.c index 49da089b5de9..cf4330b352ef 100644 --- a/drivers/hwmon/sht15.c +++ b/drivers/hwmon/sht15.c @@ -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; @@ -129,6 +170,40 @@ struct sht15_data { }; /** + * 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 * @@ -268,6 +343,26 @@ static int sht15_soft_reset(struct sht15_data *data) } /** + * 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) |