Hello,
On Fri, Jul 08, 2022 at 11:28:35AM +0200, Lars-Peter Clausen wrote:
> On 7/8/22 10:02, Uwe Kleine-König wrote:
> > Hello,
> >
> > the ADS7950 has a register bit (called TI_ADS7950_CR_RANGE_5V in the
> > driver) that selects the input range. Depending on that bit the input
> > range is either [0 .. V_{REF}] or [0 .. 2 * V_{REF}].
> >
> > The driver currently defaults to setting that bit, so the range is the
> > big one.
> >
> > On a machine here however I know the input is in the smaller range and
> > I'd like to benefit from the higher resolution of the small range. I
> > wonder how to make this tunable. Should that be done using a firmware
> > property? ("single-input-range" vs. "double-input-range"? Or input-range
> > = <1> vs. input-range = <2> which better matches the data sheet that
> > calls the two modes "Range 1 (0 to V_{REF})" and "Range 2 (0 to
> > 2xV_{REF})") Or should this be made tunable via sysfs? (E.g. by writing
> > to the scale property? Or a separate property?)
>
> Its a bit of a tricky one. You can find arguments for and against either.
> Like "devicetree is for hardware description and not application specific
> configuration data", or "I know which setting I want to use, having the
> kernel apply it makes it a lot easier".
The latter is usually not a good reason that the dt people would accept
:-)
> What we've done in the past in the IIO framework is to make the scale
> property writable for such devices. Together with a scale_available property
> to list valid options. This is the most flexible option as it allows to
> change the setting at runtime for applications where it is required.
Which driver would you recommend me to study for that approach?
> Maybe the right solution is a mix of both, have the property writable by
> default, but allow firmware to restrict the available options based on what
> the system designer though makes sense. E.g. on some boards having the
> ability to switch at runtime makes sense, on others it does not.
I can imagine that the board designer says: The input range is 0..5V, so
better don't restrict the range to 0..2.5V. And I'd expect the dt people
to accept such a binding. Unfortunately for me that's the wrong
direction :-)
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | https://www.pengutronix.de/ |
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