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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 v5] drivers: hwmon: max31827: Add PEC support
Date: Thu, 30 May 2024 14:25:05 +0300
Message-ID: <20240530112505.14831-1-radu.sabau@analog.com>
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Add support for PEC by configuring chip accordingly to the hwmon core
PEC attribute handling.
Add chip_write function to be used by max31827_write when setting
the attribute.

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.
v5:
 *Adapt driver to the new hwmon PEC attribute handling from the hwmon core.
---
 Documentation/hwmon/max31827.rst | 13 ++++++++++---
 drivers/hwmon/max31827.c         | 17 ++++++++++++++++-
 2 files changed, 26 insertions(+), 4 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..4a5f86afd84e 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)
@@ -332,6 +333,18 @@ static int max31827_read(struct device *dev, enum hwmon_sensor_types type,
 	return ret;
 }
 
+static int max31827_chip_write(struct *regmap, u32 attr, long val)
+{
+	switch (attr) {
+	case hwmon_chip_pec:
+		return regmap_update_bits(regmap, MAX31827_CONFIGURATION_REG,
+					  MAX38127_CONFIGURATION_PEC_EN_MASK,
+					  val ? MAX38127_CONFIGURATION_PEC_EN_MASK : 0);
+	default:
+		return -EOPNOTSUPP;
+	}
+}
+
 static int max31827_write(struct device *dev, enum hwmon_sensor_types type,
 			  u32 attr, int channel, long val)
 {
@@ -340,6 +353,8 @@ static int max31827_write(struct device *dev, enum hwmon_sensor_types type,
 	int ret;
 
 	switch (type) {
+	case hwmon_chip:
+		return max31827_chip_write(st->regmap, attr, val);
 	case hwmon_temp:
 		switch (attr) {
 		case hwmon_temp_enable:
@@ -583,7 +598,7 @@ static const struct hwmon_channel_info *max31827_info[] = {
 					 HWMON_T_MIN_HYST | HWMON_T_MIN_ALARM |
 					 HWMON_T_MAX | HWMON_T_MAX_HYST |
 					 HWMON_T_MAX_ALARM),
-	HWMON_CHANNEL_INFO(chip, HWMON_C_UPDATE_INTERVAL),
+	HWMON_CHANNEL_INFO(chip, HWMON_C_UPDATE_INTERVAL | HWMON_C_PEC),
 	NULL,
 };
 
-- 
2.34.1