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The INA3221 has a critical alert pin that can be controlled by the
summation control function. This function adds the single
shunt-voltage conversions for the desired channels in order to
compare the combined sum to the programmed limit. The Shunt-Voltage
Sum Limit register contains the programmed value that is compared
to the value in the Shunt-Voltage Sum register in order to
determine if the total summed limit is exceeded. If the
shunt-voltage sum limit value is exceeded, the critical alert pin
pulls low.

For the summation limit to have a meaningful value, it is necessary
to use the same shunt-resistor value on all included channels. Add a new
vendor specific property, 'ti,summation-disable', to allow specific
channels to be excluded from the summation control function if the shunt
resistor is different to other channels or the channel should not be
considered for triggering the critical alert pin.

Note that the ina3221 has always supported summing the various input
channels and summation is enabled by default if the shunt-resistor
values are the same. This change simply provides a way to exclude
inputs from the summation. If this property is not populated, then the
functionality of the driver does not change.
Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Ninad Malwade <nmalwade@nvidia.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230929103650.86074-3-jonathanh@nvidia.com

Signed-off-by: Guenter Roeck <linux@roeck-us.net>