[PATCH 5/6] iio:common:ms_sensors:ms_sensors_i2c: add support for alternative PROM layout

[Alexandre Belloni <alexandre.belloni@xxxxxxxxxxx>]

Currently, only the 112bit PROM on 7 words is supported. However the ms58xx
family also have devices with a 128bit PROM on 8 words. See AN520:
C-CODE EXAMPLE FOR MS56XX, MS57XX (EXCEPT ANALOG SENSOR), AND MS58XX SERIES
PRESSURE SENSORS and the various device datasheets.

The difference is that the CRC is the 4 LSBs of word7 instead of being the
4 MSBs of word0.

Signed-off-by: Alexandre Belloni <alexandre.belloni@xxxxxxxxxxx>
---
 .../iio/common/ms_sensors/ms_sensors_i2c.c    | 70 ++++++++++++++++---
 1 file changed, 59 insertions(+), 11 deletions(-)

diff --git a/drivers/iio/common/ms_sensors/ms_sensors_i2c.c b/drivers/iio/common/ms_sensors/ms_sensors_i2c.c
index 872f90459e2e..d97ca3e1b1d7 100644
--- a/drivers/iio/common/ms_sensors/ms_sensors_i2c.c
+++ b/drivers/iio/common/ms_sensors/ms_sensors_i2c.c
@@ -488,21 +488,18 @@ int ms_sensors_ht_read_humidity(struct ms_ht_dev *dev_data,
 EXPORT_SYMBOL(ms_sensors_ht_read_humidity);
 
 /**
- * ms_sensors_tp_crc_valid() - CRC check function for
+ * ms_sensors_tp_crc4() - Calculate PROM CRC for
  *     Temperature and pressure devices.
  *     This function is only used when reading PROM coefficients
  *
  * @prom:	pointer to PROM coefficients array
  *
- * Return: True if CRC is ok.
+ * Return: CRC.
  */
-static bool ms_sensors_tp_crc_valid(u16 *prom)
+static u8 ms_sensors_tp_crc4(u16 *prom)
 {
 	unsigned int cnt, n_bit;
-	u16 n_rem = 0x0000, crc_read = prom[0], crc = (*prom & 0xF000) >> 12;
-
-	prom[MS_SENSORS_TP_PROM_WORDS_NB - 1] = 0;
-	prom[0] &= 0x0FFF;      /* Clear the CRC computation part */
+	u16 n_rem = 0x0000;
 
 	for (cnt = 0; cnt < MS_SENSORS_TP_PROM_WORDS_NB * 2; cnt++) {
 		if (cnt % 2 == 1)
@@ -517,10 +514,55 @@ static bool ms_sensors_tp_crc_valid(u16 *prom)
 				n_rem <<= 1;
 		}
 	}
-	n_rem >>= 12;
-	prom[0] = crc_read;
 
-	return n_rem == crc;
+	return n_rem >> 12;
+}
+
+/**
+ * ms_sensors_tp_crc_valid_112() - CRC check function for
+ *     Temperature and pressure devices for 112bit PROM.
+ *     This function is only used when reading PROM coefficients
+ *
+ * @prom:	pointer to PROM coefficients array
+ *
+ * Return: CRC.
+ */
+static bool ms_sensors_tp_crc_valid_112(u16 *prom)
+{
+	u16 w0 = prom[0], crc_read = (w0 & 0xF000) >> 12;
+	u8 crc;
+
+	prom[0] &= 0x0FFF;      /* Clear the CRC computation part */
+	prom[MS_SENSORS_TP_PROM_WORDS_NB - 1] = 0;
+
+	crc = ms_sensors_tp_crc4(prom);
+
+	prom[0] = w0;
+
+	return crc == crc_read;
+}
+
+/**
+ * ms_sensors_tp_crc_valid_128() - CRC check function for
+ *     Temperature and pressure devices for 128bit PROM.
+ *     This function is only used when reading PROM coefficients
+ *
+ * @prom:	pointer to PROM coefficients array
+ *
+ * Return: CRC.
+ */
+static bool ms_sensors_tp_crc_valid_128(u16 *prom)
+{
+	u16 w7 = prom[7], crc_read = w7 & 0x000F;
+	u8 crc;
+
+	prom[7] &= 0xFF00;      /* Clear the CRC and LSB part */
+
+	crc = ms_sensors_tp_crc4(prom);
+
+	prom[7] = w7;
+
+	return crc == crc_read;
 }
 
 /**
@@ -535,6 +577,7 @@ static bool ms_sensors_tp_crc_valid(u16 *prom)
 int ms_sensors_tp_read_prom(struct ms_tp_dev *dev_data)
 {
 	int i, ret;
+	bool valid;
 
 	for (i = 0; i < dev_data->hw->prom_len; i++) {
 		ret = ms_sensors_read_prom_word(
@@ -546,7 +589,12 @@ int ms_sensors_tp_read_prom(struct ms_tp_dev *dev_data)
 			return ret;
 	}
 
-	if (!ms_sensors_tp_crc_valid(dev_data->prom)) {
+	if (dev_data->hw->prom_len == 8)
+		valid = ms_sensors_tp_crc_valid_128(dev_data->prom);
+	else
+		valid = ms_sensors_tp_crc_valid_112(dev_data->prom);
+
+	if (!valid) {
 		dev_err(&dev_data->client->dev,
 			"Calibration coefficients crc check error\n");
 		return -ENODEV;
-- 
2.28.0