linux-kernel - Re: [PATCH] gpio: uapi: clarify default

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Date: Mon, 12 Feb 2024 17:56:07 +0800
From: Kent Gibson <warthog618@...il.com>
To: Andy Shevchenko <andy.shevchenko@...il.com>
Cc: linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org, brgl@...ev.pl,
	linus.walleij@...aro.org, andy@...nel.org
Subject: Re: [PATCH] gpio: uapi: clarify default_values being logical

On Mon, Feb 12, 2024 at 11:44:02AM +0200, Andy Shevchenko wrote:
> On Mon, Feb 12, 2024 at 11:28 AM Andy Shevchenko
> <andy.shevchenko@...il.com> wrote:
> >
> > On Mon, Feb 12, 2024 at 1:13 AM Kent Gibson <warthog618@...il.com> wrote:
> > > On Sun, Feb 11, 2024 at 06:58:14PM +0200, Andy Shevchenko wrote:
> > > > On Sun, Feb 11, 2024 at 12:14 PM Kent Gibson <warthog618@...il.com> wrote:
> > > > >
> > > > > The documentation for default_values mentions high/low which can be
> > > > > confusing, particularly when the ACTIVE_LOW flag is set.
> > > > >
> > > > > Replace high/low with active/inactive to clarify that the values are
> > > > > logical not physical.
> > > > >
> > > > > Similarly, clarify the interpretation of values in struct gpiohandle_data.
> > > >
> > > > I'm not against this particular change, but I want the entire GPIO
> > > > documentation to be aligned in the terminology aspect. Is this the
> > > > case after this patch? I.o.w. have we replaced all leftovers?
> > >
> > > Agreed. Those are the last remnants of the low/high terminolgy that I am
> > > aware of, certainly the last in gpio.h.
> > >
> > > Having a closer look to double check...
> > >
> > > Ah - it is still used in Documentation/userspace-api/gpio/sysfs.rst -
> > > not somewhere I go very often.
> > > Would you like that updated in a separate patch?
> >
> > Yes, please. For this one
> > Reviewed-by: Andy Shevchenko <andy.shevchenko@...il.com>
>
> Also
> "The values are boolean, zero for low, nonzero for high."
> https://docs.kernel.org/driver-api/gpio/consumer.html
>
> And there as well
> "With this, all the gpiod_set_(array)_value_xxx() functions interpret
> the parameter "value" as "asserted" ("1") or "de-asserted" ("0")."
> So, should we use asserted-deasserted?
>
>
> On https://docs.kernel.org/driver-api/gpio/
> "get
> returns value for signal "offset", 0=low, 1=high, or negative error
>
> ...
>
> reg_set
> output set register (out=high) for generic GPIO
>
> reg_clr
> output clear register (out=low) for generic GPIO"
> (Not sure about the last two, though)
>
> https://docs.kernel.org/driver-api/gpio/intro.html
> "Output values are writable (high=1, low=0)."
>
>
> A-ha, here is the section about this:
> https://docs.kernel.org/driver-api/gpio/intro.html#active-high-and-active-low.
>
>
> On https://docs.kernel.org/driver-api/gpio/drivers-on-gpio.html
> "ledtrig-gpio: drivers/leds/trigger/ledtrig-gpio.c will provide a LED
> trigger, i.e. a LED will turn on/off in response to a GPIO line going
> high or low (and that LED may in turn use the leds-gpio as per
> above)."
>
> So, can you re-read all of it for high/low asserted/deasserted,
> active/inactive and amend accordingly?
>

Well that got out of control quickly - I was only considering userspace
documentation, not internals nor code comments.

So, no, not today.  Looks like you've got the internals covered though.

Cheers,
Kent.