[v1,1/3] Documentation: gpio: Input mode is not true Hi-Z
Commit Message
The true Hi-Z (a.k.a. high impedance) mode is when pin is completely
disconnected from the chip. This includes input buffer as well.
Nevertheless, some hardware may not support that mode and they are
considering input only as Hi-Z, but more precisely it is an equivalent
to that, in electronics it's basically "an antenna mode".
Sligthly correct documentation to take the above into consideration.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
Documentation/driver-api/gpio/driver.rst | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
Comments
On Wed, Nov 30, 2022 at 4:55 PM Andy Shevchenko
<andriy.shevchenko@linux.intel.com> wrote:
> The true Hi-Z (a.k.a. high impedance) mode is when pin is completely
> disconnected from the chip. This includes input buffer as well.
> Nevertheless, some hardware may not support that mode and they are
> considering input only as Hi-Z, but more precisely it is an equivalent
> to that, in electronics it's basically "an antenna mode".
>
> Sligthly correct documentation to take the above into consideration.
>
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Yours,
Linus Walleij
On Sat, Dec 03, 2022 at 10:33:50AM +0100, Linus Walleij wrote:
> On Wed, Nov 30, 2022 at 4:55 PM Andy Shevchenko
> <andriy.shevchenko@linux.intel.com> wrote:
>
> > The true Hi-Z (a.k.a. high impedance) mode is when pin is completely
> > disconnected from the chip. This includes input buffer as well.
> > Nevertheless, some hardware may not support that mode and they are
> > considering input only as Hi-Z, but more precisely it is an equivalent
> > to that, in electronics it's basically "an antenna mode".
> >
> > Sligthly correct documentation to take the above into consideration.
> >
> > Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
>
> Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Bart, can you apply only the first patch from the series, on which we have
a consensus (I believe?).
On Fri, Mar 10, 2023 at 6:25 PM Andy Shevchenko
<andriy.shevchenko@linux.intel.com> wrote:
>
> On Sat, Dec 03, 2022 at 10:33:50AM +0100, Linus Walleij wrote:
> > On Wed, Nov 30, 2022 at 4:55 PM Andy Shevchenko
> > <andriy.shevchenko@linux.intel.com> wrote:
> >
> > > The true Hi-Z (a.k.a. high impedance) mode is when pin is completely
> > > disconnected from the chip. This includes input buffer as well.
> > > Nevertheless, some hardware may not support that mode and they are
> > > considering input only as Hi-Z, but more precisely it is an equivalent
> > > to that, in electronics it's basically "an antenna mode".
> > >
> > > Sligthly correct documentation to take the above into consideration.
> > >
> > > Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> >
> > Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
>
> Bart, can you apply only the first patch from the series, on which we have
> a consensus (I believe?).
>
> --
> With Best Regards,
> Andy Shevchenko
>
>
Applied, thanks!
Bart
@@ -218,10 +218,10 @@ not support open drain/open source in hardware, the GPIO library will instead
use a trick: when a line is set as output, if the line is flagged as open
drain, and the IN output value is low, it will be driven low as usual. But
if the IN output value is set to high, it will instead *NOT* be driven high,
-instead it will be switched to input, as input mode is high impedance, thus
-achieving an "open drain emulation" of sorts: electrically the behaviour will
-be identical, with the exception of possible hardware glitches when switching
-the mode of the line.
+instead it will be switched to input, as input mode is an equivalent to
+high impedance, thus achieving an "open drain emulation" of sorts: electrically
+the behaviour will be identical, with the exception of possible hardware glitches
+when switching the mode of the line.
For open source configuration the same principle is used, just that instead
of actively driving the line low, it is set to input.