linux-kernel - [PATCH] usb: typec: tcpm: Extend the matching rules on PPS APDO selection

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Message-Id: <20181217024805.122897-1-kyletso@google.com>
Date:   Mon, 17 Dec 2018 10:48:05 +0800
From:   Kyle Tso <kyletso@...gle.com>
To:     linux@...ck-us.net, heikki.krogerus@...ux.intel.com,
        gregkh@...uxfoundation.org, Adam.Thomson.Opensource@...semi.com
Cc:     badhri@...gle.com, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, Kyle Tso <kyletso@...gle.com>
Subject: [PATCH] usb: typec: tcpm: Extend the matching rules on PPS APDO selection

Current matching rules ensure that the voltage range of selected Source
Capability is entirely within the range defined in one of the Sink
Capabilities. This is reasonable but not practical because Sink may not
support wide range of voltage when sinking power while Source could
advertise its capabilities in raletively wider range. For example, a
Source PDO advertising 3.3V-11V@3A (9V Prog of Fixed Nominal Voltage)
will not be selected if the Sink requires 5V-12V@3A PPS power. However,
the Sink could work well if the requested voltage range in RDOs is
5V-11V@3A.

Currently accepted:
		|--------- source -----|
	|----------- sink ---------------|

Currently not accepted:
			|--------- source -----|
	|----------- sink ---------------|

	|--------- source -----|
		|----------- sink ---------------|

	|--------- source -----------------|
		|------ sink -------|

To improve the usability, change the matching rules to what listed
below:
a. The Source PDO is selectable if any portion of the voltage range
   overlaps one of the Sink PDO's voltage range.
b. The maximum operational voltage will be the lower one between the
   selected Source PDO and the matching Sink PDO.
c. The maximum power will be the maximum operational voltage times the
   maximum current defined in the selected Source PDO
d. Select the Source PDO with the highest maximum power

Signed-off-by: Kyle Tso <kyletso@...gle.com>

---
Changelog since v1:
- updated the commit message as suggested by Guenter Roeck <linux@...ck-us.net>
---
 drivers/usb/typec/tcpm/tcpm.c | 29 +++++++++++++++++------------
 1 file changed, 17 insertions(+), 12 deletions(-)

diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
index 3620efee2688..3001df7bd602 100644
--- a/drivers/usb/typec/tcpm/tcpm.c
+++ b/drivers/usb/typec/tcpm/tcpm.c
@@ -2213,7 +2213,8 @@ static unsigned int tcpm_pd_select_pps_apdo(struct tcpm_port *port)
 	unsigned int i, j, max_mw = 0, max_mv = 0;
 	unsigned int min_src_mv, max_src_mv, src_ma, src_mw;
 	unsigned int min_snk_mv, max_snk_mv;
-	u32 pdo;
+	unsigned int max_op_mv;
+	u32 pdo, src, snk;
 	unsigned int src_pdo = 0, snk_pdo = 0;
 
 	/*
@@ -2263,16 +2264,18 @@ static unsigned int tcpm_pd_select_pps_apdo(struct tcpm_port *port)
 					continue;
 				}
 
-				if (max_src_mv <= max_snk_mv &&
-				    min_src_mv >= min_snk_mv) {
+				if (min_src_mv <= max_snk_mv &&
+				    max_src_mv >= min_snk_mv) {
+					max_op_mv = min(max_src_mv, max_snk_mv);
+					src_mw = (max_op_mv * src_ma) / 1000;
 					/* Prefer higher voltages if available */
 					if ((src_mw == max_mw &&
-					     min_src_mv > max_mv) ||
+					     max_op_mv > max_mv) ||
 					    src_mw > max_mw) {
 						src_pdo = i;
 						snk_pdo = j;
 						max_mw = src_mw;
-						max_mv = max_src_mv;
+						max_mv = max_op_mv;
 					}
 				}
 			}
@@ -2285,14 +2288,16 @@ static unsigned int tcpm_pd_select_pps_apdo(struct tcpm_port *port)
 	}
 
 	if (src_pdo) {
-		pdo = port->source_caps[src_pdo];
-
-		port->pps_data.min_volt = pdo_pps_apdo_min_voltage(pdo);
-		port->pps_data.max_volt = pdo_pps_apdo_max_voltage(pdo);
-		port->pps_data.max_curr =
-			min_pps_apdo_current(pdo, port->snk_pdo[snk_pdo]);
+		src = port->source_caps[src_pdo];
+		snk = port->snk_pdo[snk_pdo];
+
+		port->pps_data.min_volt = max(pdo_pps_apdo_min_voltage(src),
+					      pdo_pps_apdo_min_voltage(snk));
+		port->pps_data.max_volt = min(pdo_pps_apdo_max_voltage(src),
+					      pdo_pps_apdo_max_voltage(snk));
+		port->pps_data.max_curr = min_pps_apdo_current(src, snk);
 		port->pps_data.out_volt =
-			min(pdo_pps_apdo_max_voltage(pdo), port->pps_data.out_volt);
+			min(port->pps_data.max_volt, port->pps_data.out_volt);
 		port->pps_data.op_curr =
 			min(port->pps_data.max_curr, port->pps_data.op_curr);
 	}
-- 
2.20.0.405.gbc1bbc6f85-goog