w1: w1_therm: Add support for Maxim MAX31850 thermoelement IF.

MAX31850 shares family number 0x3B with DS1825. The device is generally
compatible with DS1825 but needs a different temperature readout.
It operates always in 14 bit mode and has all 4 higher bits of the
Config register set to 1. Conversion time is 100ms.

Signed-off-by: Markus Reichl <m.reichl@fivetechno.de>
Link: https://lore.kernel.org/r/20220306145817.8753-1-m.reichl@fivetechno.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/w1/slaves/w1_therm.c b/drivers/w1/slaves/w1_therm.c
index c7b8a8e787e237e01a3e8b20326c3fbdf1873422..067692626cf072acfa533975f242331626e6573f 100644 (file)
--- a/drivers/w1/slaves/w1_therm.c
+++ b/drivers/w1/slaves/w1_therm.c
@@ -574,6 +574,41 @@ static inline int w1_DS18S20_convert_time(struct w1_slave *sl)
                return SLAVE_CONV_TIME_OVERRIDE(sl);
 }
 
+static inline int w1_DS1825_convert_time(struct w1_slave *sl)
+{
+       int ret;
+
+       if (!sl->family_data)
+               return -ENODEV; /* device unknown */
+
+       if (SLAVE_CONV_TIME_OVERRIDE(sl) != CONV_TIME_DEFAULT)
+               return SLAVE_CONV_TIME_OVERRIDE(sl);
+
+       /* Return the conversion time, depending on resolution,
+        * select maximum conversion time among all compatible devices
+        */
+       switch (SLAVE_RESOLUTION(sl)) {
+       case 9:
+               ret = 95;
+               break;
+       case 10:
+               ret = 190;
+               break;
+       case 11:
+               ret = 375;
+               break;
+       case 12:
+               ret = 750;
+               break;
+       case 14:
+               ret = 100; /* MAX31850 only. Datasheet says 100ms  */
+               break;
+       default:
+               ret = 750;
+       }
+       return ret;
+}
+
 static inline int w1_DS18B20_write_data(struct w1_slave *sl,
                                const u8 *data)
 {
@@ -594,6 +629,7 @@ static inline int w1_DS18B20_set_resolution(struct w1_slave *sl, int val)
 
        /* DS18B20 resolution is 9 to 12 bits */
        /* GX20MH01 resolution is 9 to 14 bits */
+       /* MAX31850 resolution is fixed 14 bits */
        if (val < W1_THERM_RESOLUTION_MIN || val > W1_THERM_RESOLUTION_MAX)
                return -EINVAL;
 
@@ -649,6 +685,7 @@ static inline int w1_DS18B20_get_resolution(struct w1_slave *sl)
                + W1_THERM_RESOLUTION_MIN;
        /* GX20MH01 has one special case:
         *   >=14 means 14 bits when getting resolution from bit value.
+        * MAX31850 delivers fixed 15 and has 14 bits.
         * Other devices have no more then 12 bits.
         */
        if (resolution > W1_THERM_RESOLUTION_MAX)
@@ -715,6 +752,34 @@ static inline int w1_DS18S20_convert_temp(u8 rom[9])
        return t;
 }
 
+/**
+ * w1_DS1825_convert_temp() - temperature computation for DS1825
+ * @rom: data read from device RAM (8 data bytes + 1 CRC byte)
+ *
+ * Can be called for any DS1825 compliant device.
+ * Is used by MAX31850, too
+ *
+ * Return: value in millidegrees Celsius.
+ */
+
+static inline int w1_DS1825_convert_temp(u8 rom[9])
+{
+       u16 bv;
+       s16 t;
+
+       /* Signed 16-bit value to unsigned, cpu order */
+       bv = le16_to_cpup((__le16 *)rom);
+
+       /* Config register bit 7 = 1 - MA31850 found, 14 bit resolution */
+       if (rom[4] & 0x80) {
+               /* Mask out bits 0 (Fault) and 1 (Reserved) */
+               /* Avoid arithmetic shift of signed value */
+               bv = (bv & 0xFFFC); /* Degrees, lowest 4 bits are 2^-1, 2^-2 and 2 zero bits */
+       }
+       t = (s16)bv;    /* Degrees, lowest bit is 2^-4 */
+       return (int)t * 1000 / 16;      /* Sign-extend to int; millidegrees */
+}
+
 /* Device capability description */
 /* GX20MH01 device shares family number and structure with DS18B20 */
 
@@ -757,9 +822,10 @@ static struct w1_therm_family_converter w1_therm_families[] = {
                .bulk_read                      = false
        },
        {
+               /* Also used for MAX31850 */
                .f                              = &w1_therm_family_DS1825,
-               .convert                        = w1_DS18B20_convert_temp,
-               .get_conversion_time    = w1_DS18B20_convert_time,
+               .convert                        = w1_DS1825_convert_temp,
+               .get_conversion_time    = w1_DS1825_convert_time,
                .set_resolution         = w1_DS18B20_set_resolution,
                .get_resolution         = w1_DS18B20_get_resolution,
                .write_data                     = w1_DS18B20_write_data,