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google/gru: drive WLAN_MODULE_RST# low as early as possible

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GPIO1_B3 (WLAN_MODULE_RST#) defaults as a pull-up input, but it is also
"pulled up" by 1.8V_WLAN. However, 1.8V_WLAN remains low for some time
during early boot. This leaves the signal floating somewhere in the
middle.

This has two potential issues:
(1) we're leaking some power for some (hopefully) short period of time
(2) we are possibly screwing with the Wifi power sequence; we aren't
    supposed to deassert PDn (i.e., MODULE_RST#) until all the rails
    have fully ramped for some period of time

Neither of the above issues are likely to be significant, but it is nice
to fix, I expect.

BRANCH=gru
BUG=chrome-os-partner:54026
TEST=measure WLAN_MODULE_RST# on scope at boot time

Change-Id: I120e26ad0ca486a326874986e142dcaee965b62d
Signed-off-by: Brian Norris <briannorris@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/388009
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
This commit is contained in:
Brian Norris 2016-09-21 18:16:54 -07:00 • committed by chrome-bot
parent abcba216a9
commit 0e890a2787
1 changed files with 11 additions and 0 deletions
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11
src/mainboard/google/gru/mainboard.c
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@ -29,6 +29,16 @@
#include "board.h"
/*
* Wifi's PDN/RST line is pulled down by its (unpowered) voltage rails, but
* this reset pin is pulled up by default. Let's drive it low as early as we
* can.
*/
static void deassert_wifi_power(void)
{
gpio_output(GPIO(1, B, 3), 0); /* Assert WLAN_MODULE_RST# */
}
static void configure_emmc(void)
{
/* Host controller does not support programmable clock generator.
@ -236,6 +246,7 @@ static void setup_usb(void)
static void mainboard_init(device_t dev)
{
deassert_wifi_power();
configure_sdmmc();
configure_emmc();
configure_codec();