[PATCH v2 1/3] usb: typec: tcpm: Correct the responses in SVDM Version 2.0 DFP

[Kyle Tso <kyletso@google.com>]

In USB PD Spec Rev 3.1 Ver 1.0, section "6.12.5 Applicability of
Structured VDM Commands", DFP is allowed and recommended to respond to
Discovery Identity with ACK. And in section "6.4.4.2.5.1 Commands other
than Attention", NAK should be returned only when receiving Messages
with invalid fields, Messages in wrong situation, or unrecognize
Messages.

Still keep the original design for SVDM Version 1.0 for backward
compatibilities.

Fixes: 193a68011fdc ("staging: typec: tcpm: Respond to Discover Identity commands")
Signed-off-by: Kyle Tso <kyletso@google.com>
Acked-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
---
changes since v1:
- no code change
- add Acked-by tag

 drivers/usb/typec/tcpm/tcpm.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
index 0db685d5d9c0..617f48cdd90c 100644
--- a/drivers/usb/typec/tcpm/tcpm.c
+++ b/drivers/usb/typec/tcpm/tcpm.c
@@ -1575,19 +1575,25 @@ static int tcpm_pd_svdm(struct tcpm_port *port, struct typec_altmode *adev,
 			if (PD_VDO_VID(p[0]) != USB_SID_PD)
 				break;
 
-			if (PD_VDO_SVDM_VER(p[0]) < svdm_version)
+			if (PD_VDO_SVDM_VER(p[0]) < svdm_version) {
 				typec_partner_set_svdm_version(port->partner,
 							       PD_VDO_SVDM_VER(p[0]));
+				svdm_version = PD_VDO_SVDM_VER(p[0]);
+			}
 
 			tcpm_ams_start(port, DISCOVER_IDENTITY);
-			/* 6.4.4.3.1: Only respond as UFP (device) */
-			if (port->data_role == TYPEC_DEVICE &&
+			/*
+			 * PD2.0 Spec 6.10.3: respond with NAK as DFP (data host)
+			 * PD3.1 Spec 6.4.4.2.5.1: respond with NAK if "invalid field" or
+			 * "wrong configuation" or "Unrecognized"
+			 */
+			if ((port->data_role == TYPEC_DEVICE || svdm_version >= SVDM_VER_2_0) &&
 			    port->nr_snk_vdo) {
 				/*
 				 * Product Type DFP and Connector Type are not defined in SVDM
 				 * version 1.0 and shall be set to zero.
 				 */
-				if (typec_get_negotiated_svdm_version(typec) < SVDM_VER_2_0)
+				if (svdm_version < SVDM_VER_2_0)
 					response[1] = port->snk_vdo[0] & ~IDH_DFP_MASK
 						      & ~IDH_CONN_MASK;
 				else
-- 
2.32.0.rc0.204.g9fa02ecfa5-goog