From: Jerome Oufella <jerome.oufella@xxxxxxxxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/hwmon/sht15 | 9 ++-
drivers/hwmon/sht15.c | 192 ++++++++++++++++++++++++++++++++++++++++-----
include/linux/sht15.h | 2 +
3 files changed, 183 insertions(+), 20 deletions(-)
diff --git a/Documentation/hwmon/sht15 b/Documentation/hwmon/sht15
index a9e36e3..d0403f5 100644
--- a/Documentation/hwmon/sht15
+++ b/Documentation/hwmon/sht15
@@ -5,6 +5,7 @@ Authors:
* Wouter Horre
* Jonathan Cameron
* Vivien Didelot <vivien.didelot@xxxxxxxxxxxxxxxxxxxx>
+ * Jerome Oufella <jerome.oufella@xxxxxxxxxxxxxxxxxxxx>
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:
diff --git a/drivers/hwmon/sht15.c b/drivers/hwmon/sht15.c
index 77d25d3..1fb9588 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@xxxxxxxxxxxxxxxxxxxx>
* Vivien Didelot <vivien.didelot@xxxxxxxxxxxxxxxxxxxx>
*
* 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)
diff --git a/include/linux/sht15.h b/include/linux/sht15.h
index d836ca6..f85c7c5 100644
--- a/include/linux/sht15.h
+++ b/include/linux/sht15.h
@@ -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;
};
--
1.7.1
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