[PATCH v2] usb: typec: altmodes/displayport: correct pin assignment for UFP receptacles

[Macpaul Lin]

From: Pablo Sun <pablo.sun at mediatek.com>

Fix incorrect pin assignment values when connecting to a monitor with
Type-C receptacle instead of a plug.

According to specification, an UFP_D receptacle's pin assignment
should came from the UFP_D pin assignments field (bit 23:16), while
an UFP_D plug's assignments are described in the DFP_D pin assignments
(bit 15:8) during Mode Discovery.

For example the LG 27 UL850-W is a monitor with Type-C receptacle.
The monitor responds to MODE DISCOVERY command with following
DisplayPort Capability flag:

        dp->alt->vdo=0x140045

The existing logic only take cares of UPF_D plug case,
and would take the bit 15:8 for this 0x140045 case.

This results in an non-existing pin assignment 0x0 in
dp_altmode_configure.

To fix this problem a new set of macros are introduced
to take plug/receptacle differences into consideration.

Fixes: 0e3bb7d6894d ("usb: typec: Add driver for DisplayPort alternate mode")
Co-developed-by: Pablo Sun <pablo.sun at mediatek.com>
Signed-off-by: Pablo Sun <pablo.sun at mediatek.com>
Co-developed-by: Macpaul Lin <macpaul.lin at mediatek.com>
Signed-off-by: Macpaul Lin <macpaul.lin at mediatek.com>
Reviewed-by: Guillaume Ranquet <granquet at baylibre.com>
Reviewed-by: Heikki Krogerus <heikki.krogerus at linux.intel.com>
Cc: stable at vger.kernel.org
---
Changes in v2:
 - Fix commit message.
  - Remove duplicate "From:" tag.
  - Add "Fixes:" tag.
  - Add more "Reviewed-by:" tag. 

 drivers/usb/typec/altmodes/displayport.c | 4 ++--
 include/linux/usb/typec_dp.h             | 5 +++++
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/typec/altmodes/displayport.c b/drivers/usb/typec/altmodes/displayport.c
index 9360ca177c7d..8dd0e505ef99 100644
--- a/drivers/usb/typec/altmodes/displayport.c
+++ b/drivers/usb/typec/altmodes/displayport.c
@@ -98,8 +98,8 @@ static int dp_altmode_configure(struct dp_altmode *dp, u8 con)
 	case DP_STATUS_CON_UFP_D:
 	case DP_STATUS_CON_BOTH: /* NOTE: First acting as DP source */
 		conf |= DP_CONF_UFP_U_AS_UFP_D;
-		pin_assign = DP_CAP_DFP_D_PIN_ASSIGN(dp->alt->vdo) &
-			     DP_CAP_UFP_D_PIN_ASSIGN(dp->port->vdo);
+		pin_assign = DP_CAP_PIN_ASSIGN_UFP_D(dp->alt->vdo) &
+				 DP_CAP_PIN_ASSIGN_DFP_D(dp->port->vdo);
 		break;
 	default:
 		break;
diff --git a/include/linux/usb/typec_dp.h b/include/linux/usb/typec_dp.h
index cfb916cccd31..8d09c2f0a9b8 100644
--- a/include/linux/usb/typec_dp.h
+++ b/include/linux/usb/typec_dp.h
@@ -73,6 +73,11 @@ enum {
 #define DP_CAP_USB			BIT(7)
 #define DP_CAP_DFP_D_PIN_ASSIGN(_cap_)	(((_cap_) & GENMASK(15, 8)) >> 8)
 #define DP_CAP_UFP_D_PIN_ASSIGN(_cap_)	(((_cap_) & GENMASK(23, 16)) >> 16)
+/* Get pin assignment taking plug & receptacle into consideration */
+#define DP_CAP_PIN_ASSIGN_UFP_D(_cap_) ((_cap_ & DP_CAP_RECEPTACLE) ? \
+			DP_CAP_UFP_D_PIN_ASSIGN(_cap_) : DP_CAP_DFP_D_PIN_ASSIGN(_cap_))
+#define DP_CAP_PIN_ASSIGN_DFP_D(_cap_) ((_cap_ & DP_CAP_RECEPTACLE) ? \
+			DP_CAP_DFP_D_PIN_ASSIGN(_cap_) : DP_CAP_UFP_D_PIN_ASSIGN(_cap_))
 
 /* DisplayPort Status Update VDO bits */
 #define DP_STATUS_CONNECTION(_status_)	((_status_) & 3)
-- 
2.18.0