diff options
| author | Julius Werner <jwerner@chromium.org> | 2020-08-05 15:27:11 -0700 |
|---|---|---|
| committer | Julius Werner <jwerner@chromium.org> | 2020-08-06 23:54:41 +0000 |
| commit | 7450790558f3b1f85e9a11df252dd27f1047bfeb (patch) | |
| tree | 4534b2e8d65d250686cd2268d5d9bd60fbd21078 /src/lib | |
| parent | 0e0273a015f57e244015c80f0fa37192f1e569f3 (diff) | |
gpio: Pull down HiZ pins after reading tristate GPIO strapping
People who know a lot more about electrons and stuff than I do tell me
that leaving a HiZ pin floating without a pull resistor may waste power.
So if we find a pin to be HiZ when reading tristate strapping GPIOs, we
should make sure the internal pull-down is enabled when we're done with
it. (For pins that are externally pulled high or low, we should continue
to leave the internal pull disabled instead.)
Signed-off-by: Julius Werner <jwerner@chromium.org>
Change-Id: I1669823c8a7faab536e0441cb4c6cfeb9f696189
Reviewed-on: https://review.coreboot.org/c/coreboot/+/44253
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Alexandru Stan <amstan@google.com>
Reviewed-by: Furquan Shaikh <furquan@google.com>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Diffstat (limited to 'src/lib')
| -rw-r--r-- | src/lib/gpio.c | 10 |
1 files changed, 6 insertions, 4 deletions
diff --git a/src/lib/gpio.c b/src/lib/gpio.c index 3f3ae60d91..801a3b3b9c 100644 --- a/src/lib/gpio.c +++ b/src/lib/gpio.c @@ -114,6 +114,12 @@ uint32_t _gpio_base3_value(const gpio_t gpio[], int num_gpio, int binary_first) printk(BIOS_DEBUG, "%c ", tristate_char[temp]); result = (result * 3) + temp; + /* Disable pull to avoid wasting power. For HiZ we leave the + pull-down enabled, since letting them float freely back and + forth may waste power in the SoC's GPIO input logic. */ + if (temp != Z) + gpio_input(gpio[index]); + /* * For binary_first we keep track of the normal ternary result * and whether we found any pin that was a Z. We also determine @@ -159,10 +165,6 @@ uint32_t _gpio_base3_value(const gpio_t gpio[], int num_gpio, int binary_first) printk(BIOS_DEBUG, "= %d (%s base3 number system)\n", result, binary_first ? "binary_first" : "standard"); - /* Disable pull up / pull down to conserve power */ - for (index = 0; index < num_gpio; ++index) - gpio_input(gpio[index]); - return result; } |