Re: [PATCH 4/4] iio: hi8435: cleanup reset gpio

[Vladimir Barinov]

On 23.05.2017 11:18, Nikita Yushchenko wrote:
> > > Reset GPIO is active low.
> > >
> > > Currently driver uses gpiod_set_value(1) to clean reset, which depends
> > > on device tree to contain GPIO_ACTIVE_HIGH - that does not match reality.
> > >
> > > This fixes driver to use _raw version of gpiod_set_value() to enforce
> > > active-low semantics despite of what's written in device tree. Allowing
> > > device tree to override that only opens possibility for errors and does
> > > not add any value.
> > >
> > > Additionally, use _cansleep version to make things work with i2c-gpio
> > > and other sleeping gpio drivers.
> > The reset gpio comes from platform hence it should be handled by DTS.
> >
> > In driver the gpio should not be raw.
> >
> > Even the hi8435 is active low but platform may invert signal (f.e. by
> > adding trigger on the circuit path).
> I see.  However - isn't this pure theoretic?  Does such case exist?
I assure you that this is frequently used.

Simply search google for "simple voltage level shifter"
It might be on PNP or NPN transistor, hence logic might be inverted.

> In vast majority of cases, GPIO polarity is chip-specific, not
> chip-use-specific.  Thus this knowlege belongs to driver and not to
> device tree describing particular chip usage.  Having this always
> defined at usage side is IMO major source of errors.
GPIO comes from SoC then "circuit path" and finally chip reset input.

What do you propose if h/w circuit path has simple voltage level shifter 
on transistor. How to differentiate PNP and NPN cases?

Regards,
Vladimir