[PATCH v4 8/9] w1_therm: adding alarm sysfs entry to set device internal alarms values

[Akira Shimahara]

Adding device alarms settings by a dedicated sysfs entry alarms (RW):
read or write TH and TL in the device RAM. Checking devices in alarm
state could be performed using the master search command.

As alarms temperature level are store in a 8 bit register on the device
and are signed values, a safe cast shall be performed using the min and
max temperature that device are able to measure. This is done by 
int_to_short inline function.

Updating doc in Documentation/ABI/testing/sysfs-driver-w1_therm
accordingly.

Signed-off-by: Akira Shimahara <akira215corp@xxxxxxxxx>
---
 .../ABI/testing/sysfs-driver-w1_therm         |  15 ++
 drivers/w1/slaves/w1_therm.c                  | 138 ++++++++++++++++++
 drivers/w1/slaves/w1_therm.h                  |  22 +++
 3 files changed, 175 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-driver-w1_therm b/Documentation/ABI/testing/sysfs-driver-w1_therm
index 279e13d..39488a4 100644
--- a/Documentation/ABI/testing/sysfs-driver-w1_therm
+++ b/Documentation/ABI/testing/sysfs-driver-w1_therm
@@ -1,3 +1,18 @@
+What:		/sys/bus/w1/devices/.../alarms
+Date:		Apr 2020
+Contact:	Akira Shimahara <akira215corp@xxxxxxxxx>
+Description:
+		(RW) read or write TH and TL (Temperature High an Low) alarms.
+		Values shall be space separated and in the device range
+		(typical -55 degC to 125 degC). Values are integer as they
+		are store in a 8bit register in the device.
+		Lowest value is automatically put to TL.
+		Once set, alarms could be search at master level, refer to
+		Documentation/w1/w1_generic.rst for detailed information
+Users:		any user space application which wants to communicate with
+		w1_term device
+
+
 What:		/sys/bus/w1/devices/.../eeprom
 Date:		Apr 2020
 Contact:	Akira Shimahara <akira215corp@xxxxxxxxx>
diff --git a/drivers/w1/slaves/w1_therm.c b/drivers/w1/slaves/w1_therm.c
index 2c89d9f..90217b1 100644
--- a/drivers/w1/slaves/w1_therm.c
+++ b/drivers/w1/slaves/w1_therm.c
@@ -68,6 +68,12 @@ module_param_named(strong_pullup, w1_strong_pullup, int, 0);
  *				(device do that automatically on power-up)
  *
  *
+ * alarms (RW) : read TH and TL (Temperature High an Low) alarms
+ *	Values shall be space separated and in the device range
+ *	(typically -55Â to 125Â)
+ *	Values are integer are they are store in a 8bit field in the device
+ *	Lowest value is automatically put to TL
+ *
  */
 
 /*
@@ -81,6 +87,7 @@ static struct attribute *w1_therm_attrs[] = {
 	&dev_attr_ext_power.attr,
 	&dev_attr_resolution.attr,
 	&dev_attr_eeprom.attr,
+	&dev_attr_alarms.attr,
 	NULL,
 };
 
@@ -89,6 +96,7 @@ static struct attribute *w1_ds18s20_attrs[] = {
 	&dev_attr_temperature.attr,
 	&dev_attr_ext_power.attr,
 	&dev_attr_eeprom.attr,
+	&dev_attr_alarms.attr,
 	NULL,
 };
 
@@ -99,6 +107,7 @@ static struct attribute *w1_ds28ea00_attrs[] = {
 	&dev_attr_ext_power.attr,
 	&dev_attr_resolution.attr,
 	&dev_attr_eeprom.attr,
+	&dev_attr_alarms.attr,
 	NULL,
 };
 
@@ -206,6 +215,7 @@ static struct w1_family w1_therm_family_DS1825 = {
 };
 
 /*----------------------Device capability description-----------------------*/
+
 static struct w1_therm_family_converter w1_therm_families[] = {
 	{
 		.f			= &w1_therm_family_DS18S20,
@@ -431,6 +441,14 @@ static inline int temperature_from_RAM(struct w1_slave *sl, u8 rom[9])
 	return 0;  /* No device family */
 }
 
+static inline s8 int_to_short(int i)
+{
+	/* Prepare to cast to short by eliminating out of range values */
+	i = i > MAX_TEMP ? MAX_TEMP : i;
+	i = i < MIN_TEMP ? MIN_TEMP : i;
+	return (s8) i;
+}
+
 /*-------------------------Interface Functions------------------------------*/
 
 static int w1_therm_add_slave(struct w1_slave *sl)
@@ -1000,6 +1018,126 @@ static ssize_t eeprom_store(struct device *device,
 	return size;
 }
 
+static ssize_t alarms_show(struct device *device,
+	struct device_attribute *attr, char *buf)
+{
+	struct w1_slave *sl = dev_to_w1_slave(device);
+	int ret = -ENODEV;
+	s8 th = 0, tl = 0;
+	struct therm_info scratchpad;
+
+	ret = read_scratchpad(sl, &scratchpad);
+
+	if (!ret)	{
+		th = scratchpad.rom[2]; // TH is byte 2
+		tl = scratchpad.rom[3]; // TL is byte 3
+	} else {
+		dev_info(device,
+			"%s: error reading alarms register %d\n",
+			__func__, ret);
+	}
+
+	return sprintf(buf, "%hd %hd\n", tl, th);
+}
+
+static ssize_t alarms_store(struct device *device,
+	struct device_attribute *attr, const char *buf, size_t size)
+{
+	struct w1_slave *sl = dev_to_w1_slave(device);
+	struct therm_info info;
+	u8 new_config_register[3];	/* array of data to be written */
+	int temp, ret = -EINVAL;
+	char *token = NULL;
+	s8 tl, th, tt;	/* 1 byte per value + temp ring order */
+	char *p_args = kmalloc(size, GFP_KERNEL);
+
+	/* Safe string copys as buf is const */
+	if (!p_args) {
+		dev_warn(device,
+			"%s: error unable to allocate memory %d\n",
+			__func__, -ENOMEM);
+		return size;
+	}
+	strcpy(p_args, buf);
+
+	/* Split string using space char */
+	token = strsep(&p_args, " ");
+
+	if (!token)	{
+		dev_info(device,
+			"%s: error parsing args %d\n", __func__, -EINVAL);
+		goto free_m;
+	}
+
+	/* Convert 1st entry to int */
+	ret = kstrtoint (token, 10, &temp);
+	if (ret) {
+		dev_info(device,
+			"%s: error parsing args %d\n", __func__, ret);
+		goto free_m;
+	}
+
+	tl = int_to_short(temp);
+
+	/* Split string using space char */
+	token = strsep(&p_args, " ");
+	if (!token)	{
+		dev_info(device,
+			"%s: error parsing args %d\n", __func__, -EINVAL);
+		goto free_m;
+	}
+	/* Convert 2nd entry to int */
+	ret = kstrtoint (token, 10, &temp);
+	if (ret) {
+		dev_info(device,
+			"%s: error parsing args %d\n", __func__, ret);
+		goto free_m;
+	}
+
+	/* Prepare to cast to short by eliminating out of range values */
+	th = int_to_short(temp);
+
+	/* Reorder if required th and tl */
+	if (tl > th) {
+		tt = tl; tl = th; th = tt;
+	}
+
+	/* Read the scratchpad to change only the required bits
+	 * (th : byte 2 - tl: byte 3)
+	 */
+	ret = read_scratchpad(sl, &info);
+	if (!ret) {
+		new_config_register[0] = th;	// Byte 2
+		new_config_register[1] = tl;	// Byte 3
+		new_config_register[2] = info.rom[4];// Byte 4
+	} else {
+		dev_info(device,
+			"%s: error reading from the slave device %d\n",
+			__func__, ret);
+		goto free_m;
+	}
+
+	/* Write data in the device RAM */
+	if (!SLAVE_SPECIFIC_FUNC(sl)) {
+		dev_info(device,
+			"%s: Device not supported by the driver %d\n",
+			__func__, -ENODEV);
+		goto free_m;
+	}
+
+	ret = SLAVE_SPECIFIC_FUNC(sl)->write_data(sl, new_config_register);
+	if (ret)
+		dev_info(device,
+			"%s: error writing to the slave device %d\n",
+			__func__, ret);
+
+free_m:
+	/* free allocated memory */
+	kfree(p_args);
+
+	return size;
+}
+
 #if IS_REACHABLE(CONFIG_HWMON)
 static int w1_read_temp(struct device *device, u32 attr, int channel,
 			long *val)
diff --git a/drivers/w1/slaves/w1_therm.h b/drivers/w1/slaves/w1_therm.h
index 6929991..d4c560a 100644
--- a/drivers/w1/slaves/w1_therm.h
+++ b/drivers/w1/slaves/w1_therm.h
@@ -40,6 +40,9 @@
 #define EEPROM_CMD_WRITE    "save"	/* cmd for write eeprom sysfs */
 #define EEPROM_CMD_READ     "restore"	/* cmd for read eeprom sysfs */
 
+#define MIN_TEMP	-55	/* min temperature that can be mesured */
+#define MAX_TEMP	125	/* max temperature that can be mesured */
+
 /*----------------------------------Structs---------------------------------*/
 
 /**
@@ -159,6 +162,13 @@ static inline int conversion_time(struct w1_slave *sl);
  */
 static inline int temperature_from_RAM(struct w1_slave *sl, u8 rom[9]);
 
+/** int_to_short() safe casting of int to short
+ * min/max values are defined by macro
+ * @param i integer to be converted to short
+ * @return a short in the range of min/max value
+ */
+static inline s8 int_to_short(int i);
+
 /*---------------------------Hardware Functions-----------------------------*/
 
 /**
@@ -277,6 +287,17 @@ static ssize_t resolution_store(struct device *device,
 static ssize_t eeprom_store(struct device *device,
 	struct device_attribute *attr, const char *buf, size_t size);
 
+/** @brief A callback function to set the alarms level
+ *  @param device represents the master device
+ */
+static ssize_t alarms_store(struct device *device,
+	struct device_attribute *attr, const char *buf, size_t size);
+
+/** @brief A callback function to get the alarms level
+ *  @return Low and High alarm, separate by one space
+ */
+static ssize_t alarms_show(struct device *device,
+	struct device_attribute *attr, char *buf);
 /*-----------------------------Attributes declarations----------------------*/
 
 static DEVICE_ATTR_RW(w1_slave);
@@ -285,6 +306,7 @@ static DEVICE_ATTR_RO(temperature);
 static DEVICE_ATTR_RO(ext_power);
 static DEVICE_ATTR_RW(resolution);
 static DEVICE_ATTR_WO(eeprom);
+static DEVICE_ATTR_RW(alarms);
 
 /*--------------------------Interface Functions-----------------------------*/
 
-- 
2.26.2