Re: [PATCH V3 2/4] dt-bindings: hwmon: ina3221: Add ti,summation-disable

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On 22/09/2023 22:06, Rob Herring wrote:
On Thu, Sep 21, 2023 at 02:08:16PM +0100, Jon Hunter wrote:
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.

You are adding this feature to the driver, but requiring a new property
to disable it. So what happens with an existing user (old DT) and a
kernel with the new feature?

Not exactly. The summation support has always been supported in the driver and is enabled (if the shunt resistors for all channels are the same). What we want to do is support summation but only for a subset of channels which is not supported today. So this new property allows us to explicitly tell the driver not to include a specific channel in the summation.



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