ps8xxx: stub out enter_low_power_mode

the ps8751 really does not behave well with explicit low power mode
commands - it enters low power mode on its own in about 2 seconds, so
there's really no need to command it into low power mode.

when the ps8751 is awake, it will take the low power command, but also
generate an alert.  when we try to read the alert register, it fails
because the chip is in low power mode, so we go through the normal
process of waking it up, including re-initializing the chip.  we then
process the alert and power down the chip again.

but this time around the i2c transaction for the power down command
fails (we don't check this status).  the reason the i2c transaction
failed is very likely because the chip processed the I2CIDLE command
and didn't complete the i2c transaction.

BRANCH=none
BUG=b:137622553
TEST=verified chip still goes to sleep on its own

Change-Id: I01b864791ae27a81a4512ddb752329e59be6a8c6
Signed-off-by: Caveh Jalali <caveh@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/1733860
Reviewed-by: Aseda Aboagye <aaboagye@chromium.org>
Reviewed-by: Jett Rink <jettrink@chromium.org>
Commit-Queue: Caveh Jalali <caveh@google.com>

1 files changed, 7 insertions, 1 deletions

diff --git a/driver/tcpm/ps8xxx.c b/driver/tcpm/ps8xxx.c
index e95a70191a..9526887b66 100644
--- a/driver/tcpm/ps8xxx.c
+++ b/driver/tcpm/ps8xxx.c
@@ -167,6 +167,12 @@ static int ps8xxx_get_chip_info(int port, int live,
 	return rv;
 }
 
+#ifdef CONFIG_USB_PD_TCPC_LOW_POWER
+static int ps8xxx_enter_low_power_mode(int port)
+{
+	return EC_SUCCESS;
+}
+#endif
 
 const struct tcpm_drv ps8xxx_tcpm_drv = {
 	.init			= &tcpci_tcpm_init,
@@ -196,7 +202,7 @@ const struct tcpm_drv ps8xxx_tcpm_drv = {
 #endif
 	.get_chip_info		= &ps8xxx_get_chip_info,
 #ifdef CONFIG_USB_PD_TCPC_LOW_POWER
-	.enter_low_power_mode	= &tcpci_enter_low_power_mode,
+	.enter_low_power_mode	= &ps8xxx_enter_low_power_mode,
 #endif
 };