[PATCH v6 1/2] hwmon: Add PEC attribute support to hardware monitoring core

[PATCH v6 1/2] hwmon: Add PEC attribute support to hardware monitoring core

[Radu Sabau]

From: Guenter Roeck <linux@roeck-us.net>

Several hardware monitoring chips optionally support Packet Error Checking
(PEC). For some chips, PEC support can be enabled simply by setting
I2C_CLIENT_PEC in the i2c client data structure. Others require chip
specific code to enable or disable PEC support.

Introduce hwmon_chip_pec and HWMON_C_PEC to simplify adding configurable
PEC support for hardware monitoring drivers. A driver can set HWMON_C_PEC
in its chip information data to indicate PEC support. If a chip requires
chip specific code to enable or disable PEC support, the driver only needs
to implement support for the hwmon_chip_pec attribute to its write
function.

The hardware monitoring core does not depend on the I2C subsystem after
this change. However, the I2C subsystem needs to be reachable. This
requires a new HWMON dependency to ensure that HWMON can only be built
as module if I2C is built as module. This should not make a practical
difference.

Cc: Radu Sabau <radu.sabau@analog.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Nuno Sa <nuno.sa@analog.com>
---
 drivers/hwmon/Kconfig |   1 +
 drivers/hwmon/hwmon.c | 136 +++++++++++++++++++++++++++++++++++++-----
 include/linux/hwmon.h |   2 +
 3 files changed, 123 insertions(+), 16 deletions(-)

diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
index e14ae18a973b..7f384a2494c9 100644
--- a/drivers/hwmon/Kconfig
+++ b/drivers/hwmon/Kconfig
@@ -6,6 +6,7 @@
 menuconfig HWMON
 	tristate "Hardware Monitoring support"
 	depends on HAS_IOMEM
+	depends on I2C || I2C=n
 	default y
 	help
 	  Hardware monitoring devices let you monitor the hardware health
diff --git a/drivers/hwmon/hwmon.c b/drivers/hwmon/hwmon.c
index 3b259c425ab7..1fdea8b1ec91 100644
--- a/drivers/hwmon/hwmon.c
+++ b/drivers/hwmon/hwmon.c
@@ -14,6 +14,7 @@
 #include <linux/err.h>
 #include <linux/gfp.h>
 #include <linux/hwmon.h>
+#include <linux/i2c.h>
 #include <linux/idr.h>
 #include <linux/kstrtox.h>
 #include <linux/list.h>
@@ -309,6 +310,103 @@ static int hwmon_attr_base(enum hwmon_sensor_types type)
 	return 1;
 }
 
+/*
+ * PEC support
+ *
+ * The 'pec' attribute is attached to I2C client devices. It is only provided
+ * if the i2c controller supports PEC.
+ *
+ * The mutex ensures that PEC configuration between i2c device and the hardware
+ * is consistent. Use a single mutex because attribute writes are supposed to be
+ * rare, and maintaining a separate mutex for each hardware monitoring device
+ * would add substantial complexity to the driver for little if any gain.
+ *
+ * The hardware monitoring device is identified as child of the i2c client
+ * device. This assumes that only a single hardware monitoring device is
+ * attached to an i2c client device.
+ */
+
+static DEFINE_MUTEX(hwmon_pec_mutex);
+
+static int hwmon_match_device(struct device *dev, void *data)
+{
+	return dev->class == &hwmon_class;
+}
+
+static ssize_t pec_show(struct device *dev, struct device_attribute *dummy,
+			char *buf)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+
+	return sprintf(buf, "%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 i2c_client *client = to_i2c_client(dev);
+	struct hwmon_device *hwdev;
+	struct device *hdev;
+	bool val;
+	int err;
+
+	err = kstrtobool(buf, &val);
+	if (err < 0)
+		return err;
+
+	hdev = device_find_child(dev, NULL, hwmon_match_device);
+	if (!hdev)
+		return -ENODEV;
+
+	mutex_lock(&hwmon_pec_mutex);
+
+	/*
+	 * If there is no write function, we assume that chip specific
+	 * handling is not required.
+	 */
+	hwdev = to_hwmon_device(hdev);
+	if (hwdev->chip->ops->write) {
+		err = hwdev->chip->ops->write(hdev, hwmon_chip, hwmon_chip_pec, 0, val);
+		if (err && err != -EOPNOTSUPP)
+			goto unlock;
+	}
+
+	if (!val)
+		client->flags &= ~I2C_CLIENT_PEC;
+	else
+		client->flags |= I2C_CLIENT_PEC;
+
+	err = count;
+unlock:
+	mutex_unlock(&hwmon_pec_mutex);
+	put_device(hdev);
+
+	return err;
+}
+
+static DEVICE_ATTR_RW(pec);
+
+static void hwmon_remove_pec(void *dev)
+{
+	device_remove_file(dev, &dev_attr_pec);
+}
+
+static int hwmon_pec_register(struct device *hdev)
+{
+	struct i2c_client *client = i2c_verify_client(hdev->parent);
+	int err;
+
+	if (!client ||
+	    !i2c_check_functionality(client->adapter, I2C_FUNC_SMBUS_PEC))
+		return 0;
+
+	err = device_create_file(&client->dev, &dev_attr_pec);
+	if (err)
+		return err;
+
+	return devm_add_action_or_reset(hdev, hwmon_remove_pec, &client->dev);
+}
+
 /* sysfs attribute management */
 
 static ssize_t hwmon_attr_show(struct device *dev,
@@ -397,10 +495,6 @@ static struct attribute *hwmon_genattr(const void *drvdata,
 	const char *name;
 	bool is_string = is_string_attr(type, attr);
 
-	/* The attribute is invisible if there is no template string */
-	if (!template)
-		return ERR_PTR(-ENOENT);
-
 	mode = ops->is_visible(drvdata, type, attr, index);
 	if (!mode)
 		return ERR_PTR(-ENOENT);
@@ -712,8 +806,8 @@ static int hwmon_genattrs(const void *drvdata,
 
 			attr = __ffs(attr_mask);
 			attr_mask &= ~BIT(attr);
-			if (attr >= template_size)
-				return -EINVAL;
+			if (attr >= template_size || !templates[attr])
+				continue;	/* attribute is invisible */
 			a = hwmon_genattr(drvdata, info->type, attr, i,
 					  templates[attr], ops);
 			if (IS_ERR(a)) {
@@ -849,16 +943,26 @@ __hwmon_device_register(struct device *dev, const char *name, void *drvdata,
 	INIT_LIST_HEAD(&hwdev->tzdata);
 
 	if (hdev->of_node && chip && chip->ops->read &&
-	    chip->info[0]->type == hwmon_chip &&
-	    (chip->info[0]->config[0] & HWMON_C_REGISTER_TZ)) {
-		err = hwmon_thermal_register_sensors(hdev);
-		if (err) {
-			device_unregister(hdev);
-			/*
-			 * Don't worry about hwdev; hwmon_dev_release(), called
-			 * from device_unregister(), will free it.
-			 */
-			goto ida_remove;
+	    chip->info[0]->type == hwmon_chip) {
+		u32 config = chip->info[0]->config[0];
+
+		if (config & HWMON_C_REGISTER_TZ) {
+			err = hwmon_thermal_register_sensors(hdev);
+			if (err) {
+				device_unregister(hdev);
+				/*
+				 * Don't worry about hwdev; hwmon_dev_release(),
+				 * called from device_unregister(), will free it.
+				 */
+				goto ida_remove;
+			}
+		}
+		if (config & HWMON_C_PEC) {
+			err = hwmon_pec_register(hdev);
+			if (err) {
+				device_unregister(hdev);
+				goto ida_remove;
+			}
 		}
 	}
 
diff --git a/include/linux/hwmon.h b/include/linux/hwmon.h
index edf96f249eb5..e94314760aab 100644
--- a/include/linux/hwmon.h
+++ b/include/linux/hwmon.h
@@ -45,6 +45,7 @@ enum hwmon_chip_attributes {
 	hwmon_chip_power_samples,
 	hwmon_chip_temp_samples,
 	hwmon_chip_beep_enable,
+	hwmon_chip_pec,
 };
 
 #define HWMON_C_TEMP_RESET_HISTORY	BIT(hwmon_chip_temp_reset_history)
@@ -60,6 +61,7 @@ enum hwmon_chip_attributes {
 #define HWMON_C_POWER_SAMPLES		BIT(hwmon_chip_power_samples)
 #define HWMON_C_TEMP_SAMPLES		BIT(hwmon_chip_temp_samples)
 #define HWMON_C_BEEP_ENABLE		BIT(hwmon_chip_beep_enable)
+#define HWMON_C_PEC			BIT(hwmon_chip_pec)
 
 enum hwmon_temp_attributes {
 	hwmon_temp_enable,
-- 
2.34.1

[PATCH v6 2/2] drivers: hwmon: max31827: Add PEC support

[Radu Sabau]

Add support for PEC by configuring the chip accordingly to the hwmon core PEC
attribute handling
Handle hwmon_chip_pec attribute writing in the max31827_write in the
hwmon_chip type switch case, approaching the same code structure
as for temp writing.

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.
v6:
 *Apply patch containing hwmon core code and rebase driver PEC patch on top
  of it.
 *Handle hwmon_chip_pec attribute write in the max31827_write function, the same
  way temp writes are handled, therefore remove the max31827_chip_write function
 *Fix typos.
---
 Documentation/hwmon/max31827.rst | 13 ++++++++++---
 drivers/hwmon/max31827.c         | 18 ++++++++++++------
 2 files changed, 22 insertions(+), 9 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..4d89b6a7060b 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)
@@ -382,7 +383,8 @@ static int max31827_write(struct device *dev, enum hwmon_sensor_types type,
 		}
 
 	case hwmon_chip:
-		if (attr == hwmon_chip_update_interval) {
+		switch (attr) {
+		case hwmon_chip_update_interval:
 			if (!st->enable)
 				return -EINVAL;
 
@@ -410,14 +412,18 @@ static int max31827_write(struct device *dev, enum hwmon_sensor_types type,
 				return ret;
 
 			st->update_interval = val;
-		}
-		break;
 
+			return 0;
+		case hwmon_chip_pec:
+			return regmap_update_bits(st->regmap, MAX31827_CONFIGURATION_REG,
+						  MAX31827_CONFIGURATION_PEC_EN_MASK,
+						  val ? MAX31827_CONFIGURATION_PEC_EN_MASK : 0);
+		default:
+			return -EOPNOTSUPP;
+		}
 	default:
 		return -EOPNOTSUPP;
 	}
-
-	return 0;
 }
 
 static ssize_t temp1_resolution_show(struct device *dev,
@@ -583,7 +589,7 @@ 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

Re: [PATCH v6 2/2] drivers: hwmon: max31827: Add PEC support

[Nuno Sá]

On Fri, 2024-05-31 at 11:46 +0300, Radu Sabau wrote:
> Add support for PEC by configuring the chip accordingly to the hwmon core PEC
> attribute handling
> Handle hwmon_chip_pec attribute writing in the max31827_write in the
> hwmon_chip type switch case, approaching the same code structure
> as for temp writing.
> 
> Signed-off-by: Radu Sabau <radu.sabau@analog.com>
> ---

Reviewed-by: Nuno Sa <nuno.sa@analog.com>

- Nuno Sá
> 

Re: [PATCH v6 2/2] drivers: hwmon: max31827: Add PEC support

[Guenter Roeck]

On Fri, May 31, 2024 at 11:46:44AM +0300, Radu Sabau wrote:
> Add support for PEC by configuring the chip accordingly to the hwmon
> core PEC attribute handling.
> 
> Handle hwmon_chip_pec attribute writing in the max31827_write in the
> hwmon_chip type switch case, using the same code structure as for
> writing temperature limits. 
> 
> Signed-off-by: Radu Sabau <radu.sabau@analog.com>
> Reviewed-by: Nuno Sa <nuno.sa@analog.com>

Applied to hwmon-next.

Thanks,
Guenter