hwmon: (tmp421) support specifying n-factor via DT

Previous patches added a way to specify some channel specific parameters
in DT and n-factor is definitely one of them. This calibration mechanism
is board specific as its value depends on the diodes/transistors being
connected to the sensor and thus the DT seems like a right fit for that
information. It is very similar to the value of shunt resistor that some
drivers allows specifying in DT.

This patch adds a possibility to set n-factor for each channel via
"n-factor" DT property in each channel subnode.

Signed-off-by: Krzysztof Adamski <krzysztof.adamski@nokia.com>
Link: https://lore.kernel.org/r/69d0bfcc5ba27c67f21d3eabfb100656a14c75b9.1634206677.git.krzysztof.adamski@nokia.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

diff --git a/drivers/hwmon/tmp421.c b/drivers/hwmon/tmp421.c
index af08bc985a130ff7bef26ad4805b68f1206d316a..4f3737d14ade5cadbca9ac07c5974522e17a17c5 100644 (file)
--- a/drivers/hwmon/tmp421.c
+++ b/drivers/hwmon/tmp421.c
@@ -34,6 +34,7 @@ enum chips { tmp421, tmp422, tmp423, tmp441, tmp442 };
 #define TMP421_STATUS_REG                      0x08
 #define TMP421_CONFIG_REG_1                    0x09
 #define TMP421_CONVERSION_RATE_REG             0x0B
+#define TMP421_N_FACTOR_REG_1                  0x21
 #define TMP421_MANUFACTURER_ID_REG             0xFE
 #define TMP421_DEVICE_ID_REG                   0xFF
 
@@ -310,6 +311,7 @@ static int tmp421_probe_child_from_dt(struct i2c_client *client,
 {
        struct device *dev = &client->dev;
        u32 i;
+       s32 val;
        int err;
 
        err = of_property_read_u32(child, "reg", &i);
@@ -329,6 +331,22 @@ static int tmp421_probe_child_from_dt(struct i2c_client *client,
 
        data->channel[i].enabled = of_device_is_available(child);
 
+       err = of_property_read_s32(child, "ti,n-factor", &val);
+       if (!err) {
+               if (i == 0) {
+                       dev_err(dev, "n-factor can't be set for internal channel\n");
+                       return -EINVAL;
+               }
+
+               if (val > 127 || val < -128) {
+                       dev_err(dev, "n-factor for channel %d invalid (%d)\n",
+                               i, val);
+                       return -EINVAL;
+               }
+               i2c_smbus_write_byte_data(client, TMP421_N_FACTOR_REG_1 + i - 1,
+                                         val);
+       }
+
        return 0;
 }