linux-kernel - [PATCH 7/8] hwmon: (pmbus/lm25066) Support configurable sense resistor values

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Date:   Tue, 28 Sep 2021 02:22:41 -0700
From:   Zev Weiss <zev@...ilderbeest.net>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Zev Weiss <zev@...ilderbeest.net>,
        Jean Delvare <jdelvare@...e.com>,
        Jonathan Corbet <corbet@....net>, linux-hwmon@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 7/8] hwmon: (pmbus/lm25066) Support configurable sense resistor values

The appropriate mantissa values for the lm25066 family's direct-format
current and power readings are a function of the sense resistor
employed between the SENSE and VIN pins of the chip.  Instead of
assuming that resistance is always the same 1mOhm as used in the
datasheet, allow it to be configured via a device-tree property
("shunt-resistor-micro-ohms").

Signed-off-by: Zev Weiss <zev@...ilderbeest.net>
---
 Documentation/hwmon/lm25066.rst |  2 ++
 drivers/hwmon/pmbus/lm25066.c   | 12 ++++++++++++
 2 files changed, 14 insertions(+)

diff --git a/Documentation/hwmon/lm25066.rst b/Documentation/hwmon/lm25066.rst
index 9f1d7e4d3ca1..a2098eb24090 100644
--- a/Documentation/hwmon/lm25066.rst
+++ b/Documentation/hwmon/lm25066.rst
@@ -79,6 +79,8 @@ This driver does not auto-detect devices. You will have to instantiate the
 devices explicitly. Please see Documentation/i2c/instantiating-devices.rst for
 details.
 
+The shunt (sense) resistor value can be configured by a device tree property;
+see Documentation/devicetree/bindings/hwmon/pmbus/ti,lm25066.yaml for details.
 
 Platform data support
 ---------------------
diff --git a/drivers/hwmon/pmbus/lm25066.c b/drivers/hwmon/pmbus/lm25066.c
index 18d5a76f346d..29e848bcd436 100644
--- a/drivers/hwmon/pmbus/lm25066.c
+++ b/drivers/hwmon/pmbus/lm25066.c
@@ -458,6 +458,7 @@ MODULE_DEVICE_TABLE(of, lm25066_of_match);
 static int lm25066_probe(struct i2c_client *client)
 {
 	int config;
+	u32 shunt;
 	struct lm25066_data *data;
 	struct pmbus_driver_info *info;
 	const struct __coeff *coeff;
@@ -535,6 +536,17 @@ static int lm25066_probe(struct i2c_client *client)
 		info->b[PSC_POWER] = coeff[PSC_POWER].b;
 	}
 
+	/*
+	 * Values in the TI datasheets are normalized for a 1mOhm sense
+	 * resistor; assume that unless DT specifies a value explicitly.
+	 */
+	if (of_property_read_u32(client->dev.of_node,
+	                         "shunt-resistor-micro-ohms", &shunt))
+		shunt = 1000;
+
+	info->m[PSC_CURRENT_IN] = info->m[PSC_CURRENT_IN] * shunt / 1000;
+	info->m[PSC_POWER] = info->m[PSC_POWER] * shunt / 1000;
+
 	return pmbus_do_probe(client, info);
 }
 
-- 
2.33.0