[PATCH v3 1/2] hwmon: (adt7475) Added attenuator bypass support

[Logan Shaw <logan.shaw@alliedtelesis.co.nz>]

Added support for reading DTS properties to set attenuators on
device probe for the ADT7473, ADT7475, ADT7476, and ADT7490.

Signed-off-by: Logan Shaw <logan.shaw@alliedtelesis.co.nz>
---
---
 drivers/hwmon/adt7475.c | 76 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 76 insertions(+)

diff --git a/drivers/hwmon/adt7475.c b/drivers/hwmon/adt7475.c
index 6c64d50c9aae..2bb787acb363 100644
--- a/drivers/hwmon/adt7475.c
+++ b/drivers/hwmon/adt7475.c
@@ -19,6 +19,7 @@
 #include <linux/hwmon-vid.h>
 #include <linux/err.h>
 #include <linux/jiffies.h>
+#include <linux/of.h>
 #include <linux/util_macros.h>
 
 /* Indexes for the sysfs hooks */
@@ -1457,6 +1458,76 @@ static int adt7475_update_limits(struct i2c_client *client)
 	return 0;
 }
 
+/**
+ * Attempts to read a u32 property from the DTS, if there is no error and
+ * the properties value is zero then the bit given by parameter bit_index
+ * is cleared in the parameter config. If the value is non-zero then the bit
+ * is set.
+ * 
+ * If reading the dts property returned an error code then it is returned and
+ * the config parameter is not modified.
+ */
+static int modify_config_from_dts_prop(const struct i2c_client *client,
+								char *dts_property, u8 *config, u8 bit_index) {
+	u32 is_attenuator_bypassed = 0;
+	int ret = of_property_read_u32(client->dev.of_node, dts_property,
+									&is_attenuator_bypassed);
+
+	if (! ret) {
+			if (is_attenuator_bypassed)
+		*config |= (1 << bit_index);
+	else
+		*config &= ~(1 << bit_index);
+	}
+
+	return ret;
+}
+
+/**
+ * Reads all individual voltage input bypass attenuator properties from the
+ * DTS, and if the property is present the corresponding bit is set in the
+ * register.
+
+ * Properties are in the form of "bypass-attenuator-inx", where x is an
+ * integer from the set {0, 1, 3, 4} (can not bypass in2 attenuator).
+.* 
+ * The adt7473 and adt7475 only support bypassing in1.
+ * 
+ * Returns a negative error code if there was an error writing to the register.
+ */
+static int load_all_bypass_attenuators(const struct i2c_client *client, 
+					      int chip, u8 *config2, u8 *config4)
+{
+	u8 config2_copy = *config2;
+	u8 config4_copy = *config4;
+
+	if (chip == adt7476 || chip == adt7490) {
+		modify_config_from_dts_prop(client, "bypass-attenuator-in0",
+									&config4_copy, 4);
+		modify_config_from_dts_prop(client, "bypass-attenuator-in1",
+									&config4_copy, 5);
+		modify_config_from_dts_prop(client, "bypass-attenuator-in3",
+									&config4_copy, 6);
+		modify_config_from_dts_prop(client, "bypass-attenuator-in4",
+									&config4_copy, 7);
+
+		if (i2c_smbus_write_byte_data(client, REG_CONFIG4, config4_copy) < 0)
+			return -EREMOTEIO;
+
+		*config4 = config4_copy;
+	} else if (chip == adt7473 || chip == adt7475) {
+		modify_config_from_dts_prop(client, "bypass-attenuator-in1",
+									&config2_copy, 5);
+
+		if (i2c_smbus_write_byte_data(client, REG_CONFIG2, config2_copy) < 0)
+			return -EREMOTEIO;
+
+		*config2 = config2_copy;
+	}
+
+	return 0;
+}
+
 static int adt7475_probe(struct i2c_client *client,
 			 const struct i2c_device_id *id)
 {
@@ -1546,6 +1617,11 @@ static int adt7475_probe(struct i2c_client *client,
 
 	/* Voltage attenuators can be bypassed, globally or individually */
 	config2 = adt7475_read(REG_CONFIG2);
+	if (load_all_bypass_attenuators(client, chip,
+						&config2, &(data->config4)) < 0)
+		dev_warn(&client->dev,
+			 "Error setting bypass attenuator bits\n");
+
 	if (config2 & CONFIG2_ATTN) {
 		data->bypass_attn = (0x3 << 3) | 0x3;
 	} else {
-- 
2.25.0