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Date:   Mon, 17 May 2021 16:36:09 -0700
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Subject: [PATCH v1 2/2] usb: typec: tcpm: Add module parameter to wrap around logs
From:   Badhri Jagan Sridharan <badhri@google.com>
To:     Guenter Roeck <linux@roeck-us.net>,
        Heikki Krogerus <heikki.krogerus@linux.intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
        Kyle Tso <kyletso@google.com>,
        Badhri Jagan Sridharan <badhri@google.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

When the buffer is full, TCPM stops logging into the buffer.
This change adds log_wraparound module parameter which when set
flushes out the oldest log entries (FIFO) to make way for the
newer ones.

Signed-off-by: Badhri Jagan Sridharan <badhri@google.com>
---
 drivers/usb/typec/tcpm/tcpm.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
index b79194919b27..a369decade60 100644
--- a/drivers/usb/typec/tcpm/tcpm.c
+++ b/drivers/usb/typec/tcpm/tcpm.c
@@ -38,6 +38,10 @@ static bool modparam_log_misc_dev;
 module_param_named(log_misc_dev, modparam_log_misc_dev, bool, 0444);
 MODULE_PARM_DESC(log_misc_dev, "Expose tcpm logs through misc device");
 
+static bool modparam_log_wraparound;
+module_param_named(log_wraparound, modparam_log_wraparound, bool, 0444);
+MODULE_PARM_DESC(log_wraparound, "Wrap around logs");
+
 #define FOREACH_STATE(S)			\
 	S(INVALID_STATE),			\
 	S(TOGGLING),			\
@@ -597,7 +601,7 @@ static void _tcpm_log(struct tcpm_port *port, const char *fmt, va_list args)
 
 	vsnprintf(tmpbuffer, sizeof(tmpbuffer), fmt, args);
 
-	if (tcpm_log_full(port)) {
+	if (!modparam_log_wraparound && tcpm_log_full(port)) {
 		port->logbuffer_head = max(port->logbuffer_head - 1, 0);
 		strcpy(tmpbuffer, "overflow");
 	}
@@ -621,6 +625,9 @@ static void _tcpm_log(struct tcpm_port *port, const char *fmt, va_list args)
 		  (unsigned long)ts_nsec, rem_nsec / 1000,
 		  tmpbuffer);
 	port->logbuffer_head = (port->logbuffer_head + 1) % LOG_BUFFER_ENTRIES;
+	if (modparam_log_wraparound && port->logbuffer_head == port->logbuffer_tail)
+		port->logbuffer_tail =
+			(port->logbuffer_tail + 1) % LOG_BUFFER_ENTRIES;
 
 abort:
 	mutex_unlock(&port->logbuffer_lock);
@@ -733,7 +740,7 @@ static int tcpm_log_show(struct seq_file *s, void *v)
 		seq_printf(s, "%s\n", port->logbuffer[tail]);
 		tail = (tail + 1) % LOG_BUFFER_ENTRIES;
 	}
-	if (!seq_has_overflowed(s))
+	if (!modparam_log_wraparound && !seq_has_overflowed(s))
 		port->logbuffer_tail = tail;
 	mutex_unlock(&port->logbuffer_lock);
 
-- 
2.31.1.751.gd2f1c929bd-goog