servo_v4: Minor update the PD policy and comments

Update the PD policy and comments:
 * Only allow data role swap on DUT port;
 * Remove the dts mode condition to initiate a data role swap
   (not necessary to limit it to dts mode).

BRANCH=servo
BUG=b:135691171
TEST=Checked the CHG port is always UFP.
TEST=Checked the DUT port is SRC/UFP, a data role swap happened (but
it was initiated by DUT).

Change-Id: I668703209301a9542e94768f31f6ce8e2d9eb0f4
Signed-off-by: Wai-Hong Tam <waihong@google.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/1682918
Reviewed-by: Aseda Aboagye <aaboagye@chromium.org>
(cherry picked from commit 598c2c11d4024ed84fa1b185ef447c8a732c8535)
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/1686278

1 files changed, 17 insertions, 9 deletions

diff --git a/board/servo_v4/usb_pd_policy.c b/board/servo_v4/usb_pd_policy.c
index 0ae2552e02..9a781c6534 100644
--- a/board/servo_v4/usb_pd_policy.c
+++ b/board/servo_v4/usb_pd_policy.c
@@ -632,23 +632,32 @@ int pd_check_power_swap(int port)
 
 int pd_check_data_swap(int port, int data_role)
 {
-	/* Servo can allow data role swaps */
+	/*
+	 * Servo should allow data role swaps to let DUT see the USB hub, but
+	 * doing it on CHG port is a waste as its data lines is unconnected.
+	 */
+	if (port == CHG)
+		return 0;
+
 	return 1;
 }
 
 void pd_execute_data_swap(int port, int data_role)
 {
-	/* Should we do something here? */
+	/*
+	 * TODO(b/137887386): Turn on the fastboot/DFU path when data swap to
+	 * DFP?
+	 */
 }
 
 void pd_check_pr_role(int port, int pr_role, int flags)
 {
 	/*
-	 * TODO(crosbug.com/p/60792): CHG port can't do a power swap as it's SNK
-	 * only. DUT port should be able to support a power role swap, but VBUS
-	 * will need to be present. For now, don't allow swaps on either port.
+	 * Don't define any policy to initiate power role swap.
+	 *
+	 * CHG port is SNK only. DUT port requires a user to switch its
+	 * role by commands. So don't do anything implicitly.
 	 */
-
 }
 
 void pd_check_dr_role(int port, int dr_role, int flags)
@@ -656,9 +665,8 @@ void pd_check_dr_role(int port, int dr_role, int flags)
 	if (port == CHG)
 		return;
 
-	/* If DFP, try to switch to UFP */
-	if ((flags & PD_FLAGS_PARTNER_DR_DATA) && dr_role == PD_ROLE_DFP &&
-	    !disable_dts_mode)
+	/* If DFP, try to switch to UFP, to let DUT see the USB hub. */
+	if ((flags & PD_FLAGS_PARTNER_DR_DATA) && dr_role == PD_ROLE_DFP)
 		pd_request_data_swap(port);
 }