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

Linus Walleij
2016-04-20T14:56:54Z

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