w1_therm: adding bulk read support to trigger multiple conversion on bus

Adding bulk read support:
Sending a 'trigger' command in the dedicated sysfs entry of bus master
device send a conversion command for all the slaves on the bus. The sysfs
entry is added as soon as at least one device supporting this feature
is detected on the bus.

The behavior of the sysfs reading temperature on the device is as follow:
 * If no bulk read pending, trigger a conversion on the device, wait for
 the conversion to be done, read the temperature in device RAM
 * If a bulk read has been trigger, access directly the device RAM
This behavior is the same on the 2 sysfs entries ('temperature' and
'w1_slave').

Reading the therm_bulk_read sysfs give the status of bulk operations:
 * '-1': conversion in progress on at least 1 sensor
 * '1': conversion complete but at least one sensor has not been read yet
 * '0': no bulk operation. Reading temperature on ecah device will trigger
a conversion

As not all devices support bulk read feature, it has been added in device
family structure.

The attribute is set at master level as soon as a supporting device is
discover. It is removed when the last supported device leave the bus.
The count of supported device is kept with the static counter
bulk_read_device_counter.

A strong pull up is apply on the line if at least one device required it.
The duration of the pull up is the max time required by a device on the
line, which depends on the resolution settings of each device. The strong
pull up could be adjust with the a module parameter.

Updating documentation in Documentation/ABI/testing/sysfs-driver-w1_therm
and Documentation/w1/slaves/w1_therm.rst accordingly.
Signed-off-by: Akira Shimahara <akira215corp@gmail.com>
Link: https://lore.kernel.org/r/20200511203820.411483-1-akira215corp@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/ABI/testing/sysfs-driver-w1_therm

@@ -62,7 +62,14 @@ Date:		May 2020
 Contact:	Akira Shimahara <akira215corp@gmail.com>
 Description:
 		(RO) return the temperature in 1/1000 degC.
-		Note that the conversion duration depend on the resolution (if
+			* If a bulk read has been triggered, it will directly
+			return the temperature computed when the bulk read
+			occurred, if available. If not yet available, nothing
+			is returned (a debug kernel message is sent), you
+			should retry later on.
+			* If no bulk read has been triggered, it will trigger
+			a conversion and send the result. Note that the
+			conversion duration depend on the resolution (if
 			device support this feature). It takes 94ms in 9bits
 			resolution, 750ms for 12bits.
 Users:		any user space application which wants to communicate with
@@ -86,3 +93,24 @@ Description:
 		information.
 Users:		any user space application which wants to communicate with
 		w1_term device
+
+
+What:		/sys/bus/w1/devices/w1_bus_masterXX/therm_bulk_read
+Date:		May 2020
+Contact:	Akira Shimahara <akira215corp@gmail.com>
+Description:
+		(RW) trigger a bulk read conversion. read the status
+		*read*:
+			* '-1': conversion in progress on at least 1 sensor
+			* '1' :	conversion complete but at least one sensor
+				value has not been read yet
+			* '0' :	no bulk operation. Reading temperature will
+				trigger a conversion on each device
+		*write*: 'trigger': trigger a bulk read on all supporting
+			devices on the bus
+		Note that if a bulk read is sent but one sensor is not read
+		immediately, the next access to temperature on this device
+		will return the temperature measured at the time of issue
+		of the bulk read command (not the current temperature).
+Users:		any user space application which wants to communicate with
+		w1_term device

Documentation/w1/slaves/w1_therm.rst

@@ -34,12 +34,23 @@ If the crc matched the returned values are retained.  The second line
 displays the retained values along with a temperature in millidegrees
 Centigrade after t=.
 
-Parasite powered devices are limited to one slave performing a
-temperature conversion at a time.  If none of the devices are parasite
-powered it would be possible to convert all the devices at the same
-time and then go back to read individual sensors.  That isn't
-currently supported.  The driver also doesn't support reduced
-precision (which would also reduce the conversion time) when reading values.
+Alternatively, temperature can be read using temperature sysfs, it
+return only temperature in millidegrees Centigrade.
+
+A bulk read of all devices on the bus could be done writing 'trigger'
+in the therm_bulk_read sysfs entry at w1_bus_master level. This will
+sent the convert command on all devices on the bus, and if parasite
+powered devices are detected on the bus (and strong pullup is enable
+in the module), it will drive the line high during the longer conversion
+time required by parasited powered device on the line. Reading
+therm_bulk_read will return 0 if no bulk conversion pending,
+-1 if at least one sensor still in conversion, 1 if conversion is complete
+but at least one sensor value has not been read yet. Result temperature is
+then accessed by reading the temperature sysfs entry of each device, which
+may return empty if conversion is still in progress. Note that if a bulk
+read is sent but one sensor is not read immediately, the next access to
+temperature on this device will return the temperature measured at the
+time of issue of the bulk read command (not the current temperature).
 
 Writing a value between 9 and 12 to the sysfs w1_slave file will change the
 precision of the sensor for the next readings. This value is in (volatile)
@@ -49,6 +60,27 @@ To store the current precision configuration into EEPROM, the value 0
 has to be written to the sysfs w1_slave file. Since the EEPROM has a limited
 amount of writes (>50k), this command should be used wisely.
 
+Alternatively, resolution can be set or read (value from 9 to 12) using the
+dedicated resolution sysfs entry on each device. This sysfs entry is not
+present for devices not supporting this feature. Driver will adjust the
+correct conversion time for each device regarding to its resolution setting.
+In particular, strong pullup will be applied if required during the conversion
+duration.
+
+The write-only sysfs entry eeprom is an alternative for EEPROM operations:
+  * 'save': will save device RAM to EEPROM
+  * 'restore': will restore EEPROM data in device RAM.
+
+ext_power syfs entry allow tho check the power status of each device.
+  * '0': device parasite powered
+  * '1': device externally powered
+
+sysfs alarms allow 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.
+
 The module parameter strong_pullup can be set to 0 to disable the
 strong pullup, 1 to enable autodetection or 2 to force strong pullup.
 In case of autodetection, the driver will use the "READ POWER SUPPLY"