Fix poweron state machine in the EC

The existing state machine does the following:
- when power button is pressed it
1. powers on the AP
2. sets a timer of 1 sec and then
3. waits for power button to be released

When the timer fires it checks xpshold is set by the AP and if so
it clears the pwron signal (which is used by the AP to detect power
button is pressed).

The problem occurs when the user holds the power button for more than a
second.  The AP turns on xpshold, then notices that pwron is still on
and subsequently powers down because it thinks the power button is
pressed.  When the button is finally released, since it was held down
for more than a second, the timer routine notices that xpshold is not on
and therefore shuts down the system.

Another problem found while analysing this state machine is that loop
checking for poweroff only triggers on the rising edge of xpshold.  This
means that if the AP powers down the EC might miss a possible power
event.

Here is the proposed fix:
When the power button is pressed the EC will:
1. power on the AP
2. Check for xpshold to be asserted with a 1 sec timeout
3. If uboot is healthy xpshold should come on pretty quickly; the EC
then waits for the power button to be released in less than 8 seconds
4. If the power button is released then the EC waits for power off
events.
5. If the power button is not released it waits for upto 8 seconds
before turning off the AP.

The added wrinkle is how to address a borked uboot case.  In the case
where xpshold doesn't come on in < 1 second, the EC will allow the AP to
stay on for upto 16 seconds so that USB boot can finish.  The user must
hold the power button down until uboot boots and sets xpshold.  The
assumption here is that USB boot takes < 16 seconds.

BUG=chrome-os-partner:12748
TEST="follow instructions in bug report"

Change-Id: I5b582a6c3ae3449238e2813e4a581bd8f92dd846
Signed-off-by: Puneet Kumar <puneetster@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/31291
Reviewed-by: Vincent Palatin <vpalatin@chromium.org>
Reviewed-by: David Hendricks <dhendrix@chromium.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/board/snow/board.c b/board/snow/board.c
index 4575a17a40..b58e8cde86 100644
--- a/board/snow/board.c
+++ b/board/snow/board.c
@@ -40,7 +40,7 @@ const struct gpio_info gpio_list[GPIO_COUNT] = {
 	/* Inputs with interrupt handlers are first for efficiency */
 	{"KB_PWR_ON_L", GPIO_B, (1<<5),  GPIO_INT_BOTH, gaia_power_event},
 	{"PP1800_LDO2", GPIO_A, (1<<1),  GPIO_INT_BOTH, gaia_power_event},
-	{"XPSHOLD",     GPIO_A, (1<<3),  GPIO_INT_RISING, gaia_power_event},
+	{"XPSHOLD",     GPIO_A, (1<<3),  GPIO_INT_BOTH, gaia_power_event},
 	{"CHARGER_INT", GPIO_C, (1<<4),  GPIO_INT_FALLING, pmu_irq_handler},
 	{"LID_OPEN",    GPIO_C, (1<<13), GPIO_INT_RISING, gaia_lid_event},
 	{"SUSPEND_L",   GPIO_A, (1<<7),  GPIO_INT_BOTH, gaia_suspend_event},