linux-kernel - [PATCH AUTOSEL 5.8 26/53] media: gpio-ir-tx: spinlock is not needed to disable interrupts

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Message-Id: <20200907163220.1280412-26-sashal@kernel.org>
Date:   Mon,  7 Sep 2020 12:31:52 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Sean Young <sean@...s.org>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        Sasha Levin <sashal@...nel.org>, linux-media@...r.kernel.org
Subject: [PATCH AUTOSEL 5.8 26/53] media: gpio-ir-tx: spinlock is not needed to disable interrupts

From: Sean Young <sean@...s.org>

[ Upstream commit 1451b93223bbe3b4e9c91fca6b451d00667c5bf0 ]

During bit-banging the IR on a gpio pin, we cannot be scheduled or have
anything interrupt us, else the generated signal will be incorrect.
Therefore, we need to disable interrupts on the local cpu. This also
disables preemption.

local_irq_disable() does exactly what we need and does not require a
spinlock.

Signed-off-by: Sean Young <sean@...s.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/media/rc/gpio-ir-tx.c | 16 +++++-----------
 1 file changed, 5 insertions(+), 11 deletions(-)

diff --git a/drivers/media/rc/gpio-ir-tx.c b/drivers/media/rc/gpio-ir-tx.c
index f33b443bfa47b..c6cd2e6d8e654 100644
--- a/drivers/media/rc/gpio-ir-tx.c
+++ b/drivers/media/rc/gpio-ir-tx.c
@@ -19,8 +19,6 @@ struct gpio_ir {
 	struct gpio_desc *gpio;
 	unsigned int carrier;
 	unsigned int duty_cycle;
-	/* we need a spinlock to hold the cpu while transmitting */
-	spinlock_t lock;
 };
 
 static const struct of_device_id gpio_ir_tx_of_match[] = {
@@ -53,12 +51,11 @@ static int gpio_ir_tx_set_carrier(struct rc_dev *dev, u32 carrier)
 static void gpio_ir_tx_unmodulated(struct gpio_ir *gpio_ir, uint *txbuf,
 				   uint count)
 {
-	unsigned long flags;
 	ktime_t edge;
 	s32 delta;
 	int i;
 
-	spin_lock_irqsave(&gpio_ir->lock, flags);
+	local_irq_disable();
 
 	edge = ktime_get();
 
@@ -72,14 +69,11 @@ static void gpio_ir_tx_unmodulated(struct gpio_ir *gpio_ir, uint *txbuf,
 	}
 
 	gpiod_set_value(gpio_ir->gpio, 0);
-
-	spin_unlock_irqrestore(&gpio_ir->lock, flags);
 }
 
 static void gpio_ir_tx_modulated(struct gpio_ir *gpio_ir, uint *txbuf,
 				 uint count)
 {
-	unsigned long flags;
 	ktime_t edge;
 	/*
 	 * delta should never exceed 0.5 seconds (IR_MAX_DURATION) and on
@@ -95,7 +89,7 @@ static void gpio_ir_tx_modulated(struct gpio_ir *gpio_ir, uint *txbuf,
 	space = DIV_ROUND_CLOSEST((100 - gpio_ir->duty_cycle) *
 				  (NSEC_PER_SEC / 100), gpio_ir->carrier);
 
-	spin_lock_irqsave(&gpio_ir->lock, flags);
+	local_irq_disable();
 
 	edge = ktime_get();
 
@@ -128,19 +122,20 @@ static void gpio_ir_tx_modulated(struct gpio_ir *gpio_ir, uint *txbuf,
 			edge = last;
 		}
 	}
-
-	spin_unlock_irqrestore(&gpio_ir->lock, flags);
 }
 
 static int gpio_ir_tx(struct rc_dev *dev, unsigned int *txbuf,
 		      unsigned int count)
 {
 	struct gpio_ir *gpio_ir = dev->priv;
+	unsigned long flags;
 
+	local_irq_save(flags);
 	if (gpio_ir->carrier)
 		gpio_ir_tx_modulated(gpio_ir, txbuf, count);
 	else
 		gpio_ir_tx_unmodulated(gpio_ir, txbuf, count);
+	local_irq_restore(flags);
 
 	return count;
 }
@@ -176,7 +171,6 @@ static int gpio_ir_tx_probe(struct platform_device *pdev)
 
 	gpio_ir->carrier = 38000;
 	gpio_ir->duty_cycle = 50;
-	spin_lock_init(&gpio_ir->lock);
 
 	rc = devm_rc_register_device(&pdev->dev, rcdev);
 	if (rc < 0)
-- 
2.25.1