From: Lukas Wunner <lukas@wunner.de>
Date: Sat, 27 Oct 2018 10:15:33 +0200
Subject: pinctrl: bcm2835: Use raw spinlock for RT compatibility
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git
Git-commit: 5c6d52e15eab2e62d00e3d26c55ca5bf01f808ef
Patch-mainline: Queued in subsystem maintainer repository
References: SLE Realtime Extension

[ Upstream commit 71dfaa749f2f7c1722ebf6716d3f797a04528cba ]

The BCM2835 pinctrl driver acquires a spinlock in its ->irq_enable,
->irq_disable and ->irq_set_type callbacks.  Spinlocks become sleeping
locks with CONFIG_PREEMPT_RT_FULL=y, therefore invocation of one of the
callbacks in atomic context may cause a hard lockup if at least two GPIO
pins in the same bank are used as interrupts.  The issue doesn't occur
with just a single interrupt pin per bank because the lock is never
contended.  I'm experiencing such lockups with GPIO 8 and 28 used as
level-triggered interrupts, i.e. with ->irq_disable being invoked on
reception of every IRQ.

The critical section protected by the spinlock is very small (one bitop
and one RMW of an MMIO register), hence converting to a raw spinlock
seems a better trade-off than converting the driver to threaded IRQ
handling (which would increase latency to handle an interrupt).

Cc: Mathias Duckeck <m.duckeck@kunbus.de>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Acked-by: Julia Cartwright <julia@ni.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Mike Galbraith <mgalbraith@suse.de>
---
 drivers/pinctrl/bcm/pinctrl-bcm2835.c |   16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

--- a/drivers/pinctrl/bcm/pinctrl-bcm2835.c
+++ b/drivers/pinctrl/bcm/pinctrl-bcm2835.c
@@ -93,7 +93,7 @@ struct bcm2835_pinctrl {
 	struct pinctrl_gpio_range gpio_range;
 
 	int irq_group[BCM2835_NUM_IRQS];
-	spinlock_t irq_lock[BCM2835_NUM_BANKS];
+	raw_spinlock_t irq_lock[BCM2835_NUM_BANKS];
 };
 
 /* pins are just named GPIO0..GPIO53 */
@@ -476,10 +476,10 @@ static void bcm2835_gpio_irq_enable(stru
 	unsigned bank = GPIO_REG_OFFSET(gpio);
 	unsigned long flags;
 
-	spin_lock_irqsave(&pc->irq_lock[bank], flags);
+	raw_spin_lock_irqsave(&pc->irq_lock[bank], flags);
 	set_bit(offset, &pc->enabled_irq_map[bank]);
 	bcm2835_gpio_irq_config(pc, gpio, true);
-	spin_unlock_irqrestore(&pc->irq_lock[bank], flags);
+	raw_spin_unlock_irqrestore(&pc->irq_lock[bank], flags);
 }
 
 static void bcm2835_gpio_irq_disable(struct irq_data *data)
@@ -491,12 +491,12 @@ static void bcm2835_gpio_irq_disable(str
 	unsigned bank = GPIO_REG_OFFSET(gpio);
 	unsigned long flags;
 
-	spin_lock_irqsave(&pc->irq_lock[bank], flags);
+	raw_spin_lock_irqsave(&pc->irq_lock[bank], flags);
 	bcm2835_gpio_irq_config(pc, gpio, false);
 	/* Clear events that were latched prior to clearing event sources */
 	bcm2835_gpio_set_bit(pc, GPEDS0, gpio);
 	clear_bit(offset, &pc->enabled_irq_map[bank]);
-	spin_unlock_irqrestore(&pc->irq_lock[bank], flags);
+	raw_spin_unlock_irqrestore(&pc->irq_lock[bank], flags);
 }
 
 static int __bcm2835_gpio_irq_set_type_disabled(struct bcm2835_pinctrl *pc,
@@ -599,7 +599,7 @@ static int bcm2835_gpio_irq_set_type(str
 	unsigned long flags;
 	int ret;
 
-	spin_lock_irqsave(&pc->irq_lock[bank], flags);
+	raw_spin_lock_irqsave(&pc->irq_lock[bank], flags);
 
 	if (test_bit(offset, &pc->enabled_irq_map[bank]))
 		ret = __bcm2835_gpio_irq_set_type_enabled(pc, gpio, type);
@@ -611,7 +611,7 @@ static int bcm2835_gpio_irq_set_type(str
 	else
 		irq_set_handler_locked(data, handle_level_irq);
 
-	spin_unlock_irqrestore(&pc->irq_lock[bank], flags);
+	raw_spin_unlock_irqrestore(&pc->irq_lock[bank], flags);
 
 	return ret;
 }
@@ -1029,7 +1029,7 @@ static int bcm2835_pinctrl_probe(struct
 		for_each_set_bit(offset, &events, 32)
 			bcm2835_gpio_wr(pc, GPEDS0 + i * 4, BIT(offset));
 
-		spin_lock_init(&pc->irq_lock[i]);
+		raw_spin_lock_init(&pc->irq_lock[i]);
 	}
 
 	err = gpiochip_add_data(&pc->gpio_chip, pc);