w1: w1_therm: Add sysfs entries to control conversion time and driver features

The conversion time of common DS18B20 clones deviates from
datasheet specs. Allow adjustment and automatic measure of the
conversion time.

Add 'conv_time' sysfs attribute:
  *read*: Current conversion time in milliseconds.
  *write*:
     '0': Set default conversion time.
     '1': Measure and set the conversion time. Make a
          single temperature conversion, poll and measure
          an actual value. Measured value is increased
          by 20% for temperature drift. A new conversion
          time is returned by reading the same attribute.
     other positive value:
        Set the conversion time in milliseconds.

The setting is active until a resolution change. Then it is reset to
default conversion time for a new resolution.

Add 'features' sysfs attribute to control optional driver settings
per device. Bit masks to read/write (logical OR):
  1: Enable check for conversion success. If byte 6 of
     scratchpad memory is 0xC after conversion, and
     temperature reads 85.00 (powerup value) or 127.94
     (insufficient power) - return a conversion error.

  2: Enable poll for conversion completion. Generate read cycles
     after the conversion start and wait for 1's. In parasite
     power mode this feature is not available.

There are some clones of DS18B20 with fixed 12 bit resolution. Make the
driver verify the resolution by reading back the device after resolution
change.

Signed-off-by: Ivan Zaentsev <ivan.zaentsev@wirenboard.ru>
Acked-by: Evgeniy Polyakov <zbr@ioremap.net>
Link: https://lore.kernel.org/r/20200904160004.87710-1-ivan.zaentsev@wirenboard.ru
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 47 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-driver-w1_therm b/Documentation/ABI/testing/sysfs-driver-w1_therm
index 9b488c0afdfa..b44b51a88c5e 100644
--- a/Documentation/ABI/testing/sysfs-driver-w1_therm
+++ b/Documentation/ABI/testing/sysfs-driver-w1_therm
@@ -53,6 +53,9 @@ Description:
 			or resolution to set in bit
 			* '-xx': xx is kernel error when reading the resolution
 			* Anything else: do nothing
+		Some DS18B20 clones are fixed in 12-bit resolution, so the
+		actual resolution is read back from the chip and verified. Error
+		is reported if the results differ.
 Users:		any user space application which wants to communicate with
 		w1_term device
 
@@ -114,3 +117,47 @@ Description:
 		of the bulk read command (not the current temperature).
 Users:		any user space application which wants to communicate with
 		w1_term device
+
+
+What:		/sys/bus/w1/devices/.../conv_time
+Date:		July 2020
+Contact:	Ivan Zaentsev <ivan.zaentsev@wirenboard.ru>
+Description:
+		(RW) Get, set, or measure a temperature conversion time. The
+		setting remains active until a resolution change. Then it is
+		reset to default (datasheet) conversion time for a new
+		resolution.
+
+		*read*: Actual conversion time in milliseconds. *write*:
+			'0': Set the default conversion time from the datasheet.
+			'1': Measure and set the conversion time. Make a single
+			     temperature conversion, measure an actual value.
+			     Increase it by 20% for temperature range. A new
+			     conversion time can be obtained by reading this
+			     same attribute.
+			other positive value:
+			     Set the conversion time in milliseconds.
+
+Users:		An application using the w1_term device
+
+
+What:		/sys/bus/w1/devices/.../features
+Date:		July 2020
+Contact:	Ivan Zaentsev <ivan.zaentsev@wirenboard.ru>
+Description:
+		(RW) Control optional driver settings.
+		Bit masks to read/write (logical OR):
+
+                1: Enable check for conversion success. If byte 6 of
+                   scratchpad memory is 0xC after conversion, and
+                   temperature reads 85.00 (powerup value) or 127.94
+                   (insufficient power) - return a conversion error.
+
+                2: Enable poll for conversion completion. Generate read cycles
+                   after the conversion start and wait for 1's. In parasite
+                   power mode this feature is not available.
+
+		*read*:  Currently selected features, bitwise OR.
+		*write*: Select features, bitwise OR.
+
+Users:		An application using the w1_term device