usb_mux: Retain mux's power state on read

Following functions need to read the mux's current mode:
1. "usb_pd_control" host command and
2. "typec" console command
For reading the current mode, mux needs to exit the low power mode.

This commit ensures that the mux's power state is retained before and
after the read by saving the status of low power mode and re-entering
the low power mode depending on the status.

BUG=b:161367077
BRANCH=None
TEST=The retimer is held in low power mode when no device attached.

Signed-off-by: Ayushee <ayushee.shah@intel.com>
Change-Id: If63f7da816d58f7ff0a0a1d695e7e4fad2d14c07
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2314105
Reviewed-by: Vijay P Hiremath <vijay.p.hiremath@intel.com>
Reviewed-by: Keith Short <keithshort@chromium.org>
Commit-Queue: Keith Short <keithshort@chromium.org>

1 files changed, 14 insertions, 3 deletions

diff --git a/driver/usb_mux/usb_mux.c b/driver/usb_mux/usb_mux.c
index ebf5db4e3b..c4af3b2ed9 100644
--- a/driver/usb_mux/usb_mux.c
+++ b/driver/usb_mux/usb_mux.c
@@ -231,17 +231,28 @@ void usb_mux_set(int port, mux_state_t mux_mode,
 mux_state_t usb_mux_get(int port)
 {
 	mux_state_t mux_state;
+	bool is_low_power_mode;
+	int rv;
 
 	if (port >= board_get_usb_pd_port_count()) {
 		return USB_PD_MUX_NONE;
 	}
 
+	/* Store the status of LPM flag (low power mode) */
+	is_low_power_mode = flags[port] & USB_MUX_FLAG_IN_LPM;
+
 	exit_low_power_mode(port);
 
-	if (configure_mux(port, USB_MUX_GET_MODE, &mux_state))
-		return USB_PD_MUX_NONE;
+	rv = configure_mux(port, USB_MUX_GET_MODE, &mux_state);
+
+	/*
+	 * If the LPM flag was set prior to reading the mux state, re-enter the
+	 * low power mode.
+	 */
+	if (is_low_power_mode)
+		enter_low_power_mode(port);
 
-	return mux_state;
+	return rv ? USB_PD_MUX_NONE : mux_state;
 }
 
 void usb_mux_flip(int port)