linux-kernel - [PATCH 4.14 075/122] media: cec-gpio: select correct Signal Free Time

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Message-Id: <20191122100815.572000367@linuxfoundation.org>
Date:   Fri, 22 Nov 2019 11:28:48 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Hans Verkuil <hans.verkuil@...co.com>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.14 075/122] media: cec-gpio: select correct Signal Free Time

From: Hans Verkuil <hans.verkuil@...co.com>

[ Upstream commit c439d5c1e13dbf66cff53455432f21d4d0536c51 ]

If a receive is in progress or starts before the transmit has
a chance, then lower the Signal Free Time of the upcoming transmit
to no more than CEC_SIGNAL_FREE_TIME_NEW_INITIATOR.

This is per the specification requirements.

Signed-off-by: Hans Verkuil <hans.verkuil@...co.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/media/cec/cec-pin.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/drivers/media/cec/cec-pin.c b/drivers/media/cec/cec-pin.c
index c003b8eac6176..68fc6a24d0771 100644
--- a/drivers/media/cec/cec-pin.c
+++ b/drivers/media/cec/cec-pin.c
@@ -529,6 +529,17 @@ static enum hrtimer_restart cec_pin_timer(struct hrtimer *timer)
 			/* Start bit, switch to receive state */
 			pin->ts = ts;
 			pin->state = CEC_ST_RX_START_BIT_LOW;
+			/*
+			 * If a transmit is pending, then that transmit should
+			 * use a signal free time of no more than
+			 * CEC_SIGNAL_FREE_TIME_NEW_INITIATOR since it will
+			 * have a new initiator due to the receive that is now
+			 * starting.
+			 */
+			if (pin->tx_msg.len && pin->tx_signal_free_time >
+			    CEC_SIGNAL_FREE_TIME_NEW_INITIATOR)
+				pin->tx_signal_free_time =
+					CEC_SIGNAL_FREE_TIME_NEW_INITIATOR;
 			break;
 		}
 		if (pin->ts == 0)
@@ -690,6 +701,15 @@ static int cec_pin_adap_transmit(struct cec_adapter *adap, u8 attempts,
 {
 	struct cec_pin *pin = adap->pin;
 
+	/*
+	 * If a receive is in progress, then this transmit should use
+	 * a signal free time of max CEC_SIGNAL_FREE_TIME_NEW_INITIATOR
+	 * since when it starts transmitting it will have a new initiator.
+	 */
+	if (pin->state != CEC_ST_IDLE &&
+	    signal_free_time > CEC_SIGNAL_FREE_TIME_NEW_INITIATOR)
+		signal_free_time = CEC_SIGNAL_FREE_TIME_NEW_INITIATOR;
+
 	pin->tx_signal_free_time = signal_free_time;
 	pin->tx_msg = *msg;
 	pin->work_tx_status = 0;
-- 
2.20.1