linux-kernel - [PATCH] usb: typec: tcpm: Correct the PPS out

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Message-Id: <20190130031353.100228-1-kyletso@google.com>
Date:   Wed, 30 Jan 2019 11:13:53 +0800
From:   Kyle Tso <kyletso@...gle.com>
To:     linux@...ck-us.net, heikki.krogerus@...ux.intel.com,
        gregkh@...uxfoundation.org
Cc:     badhri@...gle.com, Adam.Thomson.Opensource@...semi.com,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Kyle Tso <kyletso@...gle.com>
Subject: [PATCH] usb: typec: tcpm: Correct the PPS out_volt calculation

When Sink negotiates PPS, the voltage range of selected PPS APDO might
not cover the previous voltage (out_volt). If the previous out_volt is
lower than the new min_volt, the output voltage in RDO might be set to
an invalid value. For instance, supposed that the previous voltage is
5V, and the new voltage range in the APDO is 7V-12V. Then the output
voltage in the RDO should not be set to 5V which is lower than the
possible min_volt 7V.

Fix this by choosing the maximal value between the previous voltage and
the new min_volt first. And ensure that this value will not exceed the
new max_volt. The new out_volt will fall within the new voltage range
while being the closest value compared to the previous out_volt.

Signed-off-by: Kyle Tso <kyletso@...gle.com>
---
 drivers/usb/typec/tcpm/tcpm.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
index f1d3e54210df..8f2af348bda5 100644
--- a/drivers/usb/typec/tcpm/tcpm.c
+++ b/drivers/usb/typec/tcpm/tcpm.c
@@ -2297,7 +2297,8 @@ static unsigned int tcpm_pd_select_pps_apdo(struct tcpm_port *port)
 					      pdo_pps_apdo_max_voltage(snk));
 		port->pps_data.max_curr = min_pps_apdo_current(src, snk);
 		port->pps_data.out_volt = min(port->pps_data.max_volt,
-					      port->pps_data.out_volt);
+					      max(port->pps_data.min_volt,
+						  port->pps_data.out_volt));
 		port->pps_data.op_curr = min(port->pps_data.max_curr,
 					     port->pps_data.op_curr);
 	}
-- 
2.20.1.495.gaa96b0ce6b-goog