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Re: [PATCH 8/8] gpio: stmpe: configure GPIO as output by default

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On Tue, Apr 19, 2016 at 2:18 PM,  <patrice.chotard@st.com> wrote:

> From: Patrice Chotard <patrice.chotard@st.com>
>
> Configures all GPIOs as output, in order to minimize power
> consumption when GPIOs are unused.
>
> Signed-off-by: Amelie DELAUNAY <amelie.delaunay@st.com>
> Signed-off-by: Patrice Chotard <patrice.chotard@st.com>

Not only do you set them all to outout but also:

> +       /* To minimize power consumption, configure unused GPIOs as outputs */
> +       for (i = 0; i < stmpe_gpio->chip.ngpio; i++)
> +               stmpe_gpio_direction_output(&stmpe_gpio->chip, i, 0);

You are driving them all low.

Now GPIO is general purpose: what if they are connected to a
line with a pull-up resistor?

That is not saving power, instead consuming more than if you
were setting them all to 1.

I am afraid this is wrong.

What you need is to be able to define in the DT (or similar)
a set of initial values for the GPIO lines, and set them to
0 for this design.

Such bindings have been discussed but no conclusion
or merged patch has emerged. Please help out in driving
a standard for this!

Yours,
Linus Walleij

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[PATCH 0/8] STMPE fixes/rework and add STMPE1600 support <patrice.chotard@st.com> - 2016-04-19 14:30 +0200
  [PATCH 7/8] gpio: stmpe: Add STMPE1600 support <patrice.chotard@st.com> - 2016-04-19 14:30 +0200
    Re: [PATCH 7/8] gpio: stmpe: Add STMPE1600 support Linus Walleij <linus.walleij@linaro.org> - 2016-04-20 17:00 +0200
      Re: [PATCH 7/8] gpio: stmpe: Add STMPE1600 support Patrice Chotard <patrice.chotard@st.com> - 2016-04-22 09:20 +0200
  [PATCH 3/8] gpio: stmpe: fix edge and rising/falling edge detection <patrice.chotard@st.com> - 2016-04-19 14:30 +0200
    Re: [PATCH 3/8] gpio: stmpe: fix edge and rising/falling edge  detection kbuild test robot <lkp@intel.com> - 2016-04-19 14:40 +0200
    Re: [PATCH 3/8] gpio: stmpe: fix edge and rising/falling edge detection Linus Walleij <linus.walleij@linaro.org> - 2016-04-20 16:40 +0200
      Re: [PATCH 3/8] gpio: stmpe: fix edge and rising/falling edge  detection Patrice Chotard <patrice.chotard@st.com> - 2016-04-21 15:50 +0200
  [PATCH 8/8] gpio: stmpe: configure GPIO as output by default <patrice.chotard@st.com> - 2016-04-19 14:30 +0200
    Re: [PATCH 8/8] gpio: stmpe: configure GPIO as output by default Linus Walleij <linus.walleij@linaro.org> - 2016-04-20 17:00 +0200
  [PATCH 2/8] mfd: stmpe: Add reset support for all STMPE variant <patrice.chotard@st.com> - 2016-04-19 14:30 +0200
    Re: [PATCH 2/8] mfd: stmpe: Add reset support for all STMPE variant Linus Walleij <linus.walleij@linaro.org> - 2016-04-20 16:40 +0200
    Re: [PATCH 2/8] mfd: stmpe: Add reset support for all STMPE variant Lee Jones <lee.jones@linaro.org> - 2016-04-26 10:20 +0200
  Re: [PATCH 0/8] STMPE fixes/rework and add STMPE1600 support Thierry Reding <thierry.reding@gmail.com> - 2016-04-19 14:50 +0200
    Re: [PATCH 0/8] STMPE fixes/rework and add STMPE1600 support Marcel Ziswiler <marcel.ziswiler@toradex.com> - 2016-04-20 20:00 +0200
  Re: [PATCH 0/8] STMPE fixes/rework and add STMPE1600 support Stephen Warren <swarren@wwwdotorg.org> - 2016-04-19 18:00 +0200
    Re: [PATCH 0/8] STMPE fixes/rework and add STMPE1600 support Patrice Chotard <patrice.chotard@st.com> - 2016-04-20 09:50 +0200
      Re: [PATCH 0/8] STMPE fixes/rework and add STMPE1600 support Stephen Warren <swarren@wwwdotorg.org> - 2016-04-20 18:10 +0200
        Re: [PATCH 0/8] STMPE fixes/rework and add STMPE1600 support Marcel Ziswiler <marcel.ziswiler@toradex.com> - 2016-04-21 05:20 +0200
    Re: [PATCH 0/8] STMPE fixes/rework and add STMPE1600 support Linus Walleij <linus.walleij@linaro.org> - 2016-04-20 16:30 +0200

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