GPIO Centralized Control Daemon

[Andrew Jeffery]

On Sun, 2017-09-17 at 14:49 -0700, Patrick Venture wrote:
> > > Those are particulars of a board that now get factored into the
> > > value.  I'm not suggesting something beyond the norms of hwmon.  It
> > > would be convenient however, if the ADC driver could be programmed to
> > > know that some sensor is gated by a GPIO and handled flipping,
> > 
> > Can you reach out to Guenter or the relevant maintainer (is this an IIO
> > device?) for ideas here?  I hadn't mentioned it but in the back of my
> > head this whole time I've been wondering about a completely in-kernel
> > solution.
> 
> I'll reach out and see if this should go into the adc driver or the
> iio-hwmon.  Since those are the paths that are involved.  The sensor
> itself it plugged into the aspeed adc, and then controlled by a
> gpio.  My initial thought is the adc should be configured to know if
> such things are required for its sensors, so that iio-hwmon wouldn't
> need to know.

My gut feeling is the other way around. There should be some higher-
level driver (i.e. still in the kernel, not in userspace) coordinating
the GPIO and the ADC such that we sample values at the appropriate time
after the GPIO has been set. The ADC driver should be well defined in
terms of the function the ADC hardware provides - gluing in random
GPIOs makes the ADC driver do things the ADC hardware itself does not
do.

I'm not across how the iio-hwmon bridge works so I don't know how
trivial it would be to re-export the sampled ADC values from this
higher-level driver as another IIO channel, but that's probably the
approach I would look at to glue it into hwmon.

That's all just off-the-cuff opinion though, so take it with a grain of
salt. Certainly talking to the IIO and hwmon maintainers is the right
approach.

Cheers,

Andrew
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