linux-kernel - [PATCH] usb: typec: tcpm: Fix sink PDO starting index for PPS APDO selection

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Date:   Tue, 17 Jul 2018 15:36:19 +0100
From:   Adam Thomson <Adam.Thomson.Opensource@...semi.com>
To:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:     <linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <support.opensource@...semi.com>
Subject: [PATCH] usb: typec: tcpm: Fix sink PDO starting index for PPS APDO
 selection

There is a bug in the sink PDO search code when trying to select
a PPS APDO. The current code actually sets the starting index for
searching to whatever value 'i' is, rather than choosing index 1
to avoid the first PDO (always 5V fixed). As a result, for sources
which support PPS but whose PPS APDO index does not match with the
supporting sink PPS APDO index for the platform, no valid PPS APDO
will be found so this feature will not be permitted.

Sadly in testing, both Source and Sink capabilities matched up and
this was missed. Code is now updated to correctly set the start
index to 1, and testing with additional PPS capable sources show
this to work as expected.

Signed-off-by: Adam Thomson <Adam.Thomson.Opensource@...semi.com>
---
 drivers/usb/typec/tcpm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/usb/typec/tcpm.c b/drivers/usb/typec/tcpm.c
index 74e0cda..4f1f421 100644
--- a/drivers/usb/typec/tcpm.c
+++ b/drivers/usb/typec/tcpm.c
@@ -2238,7 +2238,7 @@ static unsigned int tcpm_pd_select_pps_apdo(struct tcpm_port *port)
 			 * PPS APDO. Again skip the first sink PDO as this will
 			 * always be 5V 3A.
 			 */
-			for (j = i; j < port->nr_snk_pdo; j++) {
+			for (j = 1; j < port->nr_snk_pdo; j++) {
 				pdo = port->snk_pdo[j];

 				switch (pdo_type(pdo)) {
-- 
1.9.1