[RFC] usb: typec: tcpm: match source fixed pdo with sink variable pdo

[Jun Li <jun.li@nxp.com>]

This patch tries to fix the problem describled on revert patch commit[1],
suppose any supported voltage ranges of sink should be describled by
variable pdo, so instead of revert the patch of only comparing source and
sink pdo to select one source pdo, this patch adds the match between source
fixed pdo and sink variable pdo.

[1] https://www.spinics.net/lists/linux-usb/msg166366.html

CC: Hans de Goede <hdegoede@redhat.com>
CC: Guenter Roeck <linux@roeck-us.net>
CC: Heikki Krogerus <heikki.krogerus@linux.intel.com>
CC: Adam Thomson <Adam.Thomson.Opensource@diasemi.com>
CC: Badhri Jagan Sridharan <Badhri@google.com>
Signed-off-by: Li Jun <jun.li@nxp.com>
---
 drivers/usb/typec/tcpm.c | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/drivers/usb/typec/tcpm.c b/drivers/usb/typec/tcpm.c
index ef3a60d..8a74a43 100644
--- a/drivers/usb/typec/tcpm.c
+++ b/drivers/usb/typec/tcpm.c
@@ -1815,6 +1815,37 @@ static int tcpm_pd_select_pdo(struct tcpm_port *port, int *sink_pdo,
 					break;
 				}
 			}
+
+			/*
+			 * If the source pdo has the same voltage with one
+			 * fixed pdo, no need check variable pdo for it.
+			 */
+			if (j < port->nr_fixed)
+				continue;
+
+			for (j = port->nr_fixed +
+				 port->nr_batt;
+			     j < port->nr_fixed +
+				 port->nr_batt +
+				 port->nr_var;
+			     j++) {
+				if (pdo_fixed_voltage(pdo) >=
+				     pdo_min_voltage(port->snk_pdo[j]) &&
+				     pdo_fixed_voltage(pdo) <=
+				     pdo_max_voltage(port->snk_pdo[j])) {
+					ma = min_current(pdo, port->snk_pdo[j]);
+					mv = pdo_fixed_voltage(pdo);
+					mw = ma * mv / 1000;
+					if (mw > max_mw ||
+					    (mw == max_mw && mv > max_mv)) {
+						ret = 0;
+						*src_pdo = i;
+						*sink_pdo = j;
+						max_mw = mw;
+						max_mv = mv;
+					}
+				}
+			}
 		} else if (type == PDO_TYPE_BATT) {
 			for (j = port->nr_fixed;
 			     j < port->nr_fixed +