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From: Radu Sabau <radu.sabau@analog.com>
To: Jean Delvare <jdelvare@suse.com>, Guenter Roeck <linux@roeck-us.net>,
        Jonathan Corbet <corbet@lwn.net>, <linux-hwmon@vger.kernel.org>,
        <linux-doc@vger.kernel.org>, <linux-kernel@vger.kernel.org>
CC: Radu Sabau <radu.sabau@analog.com>
Subject: [PATCH v4] drivers: hwmon: max31827: Add PEC support
Date: Mon, 27 May 2024 12:29:47 +0300
Message-ID: <20240527092947.4370-1-radu.sabau@analog.com>
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Add support for PEC by attaching PEC attribute to the i2c device.
Add pec_store and pec_show function for accessing the "pec" file.

Signed-off-by: Radu Sabau <radu.sabau@analog.com>
---
Change log:
v2:
 *Rebase on top of v6.9
 *Attach pec attribute only to i2c device
 *Fix bug to attach pec attribute to i2c device if the device supports it.
v3:
 *Use only one variable to write PEC_EN bit in configuration register
 *Use regmap_set_bits to set PEC_EN bit when requested instead of
  regmap_update_bits.
 *Fix typo in commit message.
v4:
 *Use regmap_clear_bits to clear PEC_EN bit when requested instead of
  regmap_update_bits.
---
 Documentation/hwmon/max31827.rst | 13 +++++--
 drivers/hwmon/max31827.c         | 62 ++++++++++++++++++++++++++++++++
 2 files changed, 72 insertions(+), 3 deletions(-)

diff --git a/Documentation/hwmon/max31827.rst b/Documentation/hwmon/max31827.rst
index 44ab9dc064cb..9c11a9518c67 100644
--- a/Documentation/hwmon/max31827.rst
+++ b/Documentation/hwmon/max31827.rst
@@ -131,7 +131,14 @@ The Fault Queue bits select how many consecutive temperature faults must occur
 before overtemperature or undertemperature faults are indicated in the
 corresponding status bits.
 
-Notes
------
+PEC Support
+-----------
+
+When reading a register value, the PEC byte is computed and sent by the chip.
+
+PEC on word data transaction respresents a signifcant increase in bandwitdh
+usage (+33% for both write and reads) in normal conditions.
 
-PEC is not implemented.
+Since this operation implies there will be an extra delay to each
+transaction, PEC can be disabled or enabled through sysfs.
+Just write 1  to the "pec" file for enabling PEC and 0 for disabling it.
diff --git a/drivers/hwmon/max31827.c b/drivers/hwmon/max31827.c
index f8a13b30f100..c120032582ac 100644
--- a/drivers/hwmon/max31827.c
+++ b/drivers/hwmon/max31827.c
@@ -24,6 +24,7 @@
 
 #define MAX31827_CONFIGURATION_1SHOT_MASK	BIT(0)
 #define MAX31827_CONFIGURATION_CNV_RATE_MASK	GENMASK(3, 1)
+#define MAX31827_CONFIGURATION_PEC_EN_MASK	BIT(4)
 #define MAX31827_CONFIGURATION_TIMEOUT_MASK	BIT(5)
 #define MAX31827_CONFIGURATION_RESOLUTION_MASK	GENMASK(7, 6)
 #define MAX31827_CONFIGURATION_ALRM_POL_MASK	BIT(8)
@@ -475,6 +476,52 @@ static ssize_t temp1_resolution_store(struct device *dev,
 
 static DEVICE_ATTR_RW(temp1_resolution);
 
+static ssize_t pec_show(struct device *dev, struct device_attribute *devattr,
+			char *buf)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+
+	return scnprintf(buf, PAGE_SIZE, "%d\n", !!(client->flags & I2C_CLIENT_PEC));
+}
+
+static ssize_t pec_store(struct device *dev, struct device_attribute *devattr,
+			 const char *buf, size_t count)
+{
+	struct max31827_state *st = dev_get_drvdata(dev);
+	struct i2c_client *client = to_i2c_client(dev);
+	unsigned int val;
+	int err;
+
+	err = kstrtouint(buf, 10, &val);
+	if (err < 0)
+		return err;
+
+	switch (val) {
+	case 0:
+		err = regmap_clear_bits(st->regmap, MAX31827_CONFIGURATION_REG,
+					MAX31827_CONFIGURATION_PEC_EN_MASK);
+		if (err)
+			return err;
+
+		client->flags &= ~I2C_CLIENT_PEC;
+		break;
+	case 1:
+		err = regmap_set_bits(st->regmap, MAX31827_CONFIGURATION_REG,
+				      MAX31827_CONFIGURATION_PEC_EN_MASK);
+		if (err)
+			return err;
+
+		client->flags |= I2C_CLIENT_PEC;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	return count;
+}
+
+static DEVICE_ATTR_RW(pec);
+
 static struct attribute *max31827_attrs[] = {
 	&dev_attr_temp1_resolution.attr,
 	NULL
@@ -578,6 +625,11 @@ static int max31827_init_client(struct max31827_state *st,
 	return regmap_write(st->regmap, MAX31827_CONFIGURATION_REG, res);
 }
 
+static void max31827_remove_pec(void *dev)
+{
+	device_remove_file(dev, &dev_attr_pec);
+}
+
 static const struct hwmon_channel_info *max31827_info[] = {
 	HWMON_CHANNEL_INFO(temp, HWMON_T_ENABLE | HWMON_T_INPUT | HWMON_T_MIN |
 					 HWMON_T_MIN_HYST | HWMON_T_MIN_ALARM |
@@ -627,6 +679,16 @@ static int max31827_probe(struct i2c_client *client)
 	if (err)
 		return err;
 
+	if (i2c_check_functionality(client->adapter, I2C_FUNC_SMBUS_PEC)) {
+		err = device_create_file(dev, &dev_attr_pec);
+		if (err)
+			return err;
+
+		err = devm_add_action_or_reset(dev, max31827_remove_pec, dev);
+		if (err)
+			return err;
+	}
+
 	hwmon_dev = devm_hwmon_device_register_with_info(dev, client->name, st,
 							 &max31827_chip_info,
 							 max31827_groups);
-- 
2.34.1