Skip to content

Commit

Permalink
hwmon: (sht15) add support for CRC validation
Browse files Browse the repository at this point in the history 
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>
  • Loading branch information
Jerome Oufella authored and Guenter Roeck committed May 19, 2011
1 parent cc15c7e commit 82c7465
Show file tree
Hide file tree
Showing 3 changed files with 183 additions and 20 deletions.
9 changes: 8 additions & 1 deletion Documentation/hwmon/sht15
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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
Expand Down Expand Up @@ -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:
Expand Down
192 changes: 173 additions & 19 deletions drivers/hwmon/sht15.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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
Expand Down Expand Up @@ -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).
Expand All @@ -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).
Expand All @@ -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;
Expand All @@ -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
Expand Down Expand Up @@ -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.
Expand Down Expand Up @@ -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);
Expand All @@ -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;
Expand All @@ -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)
Expand All @@ -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;
}

Expand Down Expand Up @@ -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);
Expand All @@ -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);

Expand Down Expand Up @@ -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)
Expand Down
2 changes: 2 additions & 0 deletions include/linux/sht15.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -19,13 +19,15 @@
* @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.
*/
struct sht15_platform_data {
int gpio_data;
int gpio_sck;
int supply_mv;
bool checksum;
bool no_otp_reload;
bool low_resolution;
};
Expand Down

0 comments on commit 82c7465

Please sign in to comment.