hwmon: (ina3221) Add voltage conversion time settings

The CONFIG register has two 3-bit fields for conversion time
settings of Bus-voltage and Shunt-voltage, respectively. The
conversion settings, along with averaging mode, allow users
to optimize available timing requirement.

This patch adds an 'update_interval' sysfs node through the
hwmon_chip_info of hwmon core. It reflects a total hardware
conversion time:
    samples * channels * (Bus + Shunt conversion times)

Though INA3221 supports different conversion time setups for
Bus and Shunt voltages, this patch only adds the support of
a unified setting for both conversion times, by dividing the
conversion time into two equal values.

Signed-off-by: Nicolin Chen <nicoleotsuka@gmail.com>
[groeck: .rst related formatting changes in documentation]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

1 files changed, 13 insertions, 0 deletions

diff --git a/Documentation/hwmon/ina3221.rst b/Documentation/hwmon/ina3221.rst
index 1e34abb38b59..f6007ae8f4e2 100644
--- a/Documentation/hwmon/ina3221.rst
+++ b/Documentation/hwmon/ina3221.rst
@@ -46,4 +46,17 @@ samples                 Number of samples using in the averaging mode.
                         Supports the list of number of samples:
 
                           1, 4, 16, 64, 128, 256, 512, 1024
+
+update_interval         Data conversion time in millisecond, following:
+
+                          update_interval = C x S x (BC + SC)
+
+                          * C:  number of enabled channels
+                          * S:  number of samples
+                          * BC: bus-voltage conversion time in millisecond
+                          * SC: shunt-voltage conversion time in millisecond
+
+                        Affects both Bus- and Shunt-voltage conversion time.
+                        Note that setting update_interval to 0ms sets both BC
+                        and SC to 140 us (minimum conversion time).
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