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Commit 9d9fcc11 authored by Lukas Wunner's avatar Lukas Wunner Committed by Greg Kroah-Hartman
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pinctrl: bcm2835: Use raw spinlock for RT compatibility 



[ Upstream commit 3c7b30f704b6f5e53eed6bf89cf2c8d1b38b02c0 ]

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: default avatarLukas Wunner <lukas@wunner.de>
Acked-by: default avatarJulia Cartwright <julia@ni.com>
Signed-off-by: default avatarLinus Walleij <linus.walleij@linaro.org>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent 8095fe60

drivers/pinctrl/bcm/pinctrl-bcm2835.c

+8 −8
Original line number Diff line number Diff line
@@ -90,7 +90,7 @@ struct bcm2835_pinctrl { 
	struct gpio_chip gpio_chip;

	struct pinctrl_gpio_range gpio_range;



	spinlock_t irq_lock[BCM2835_NUM_BANKS];

	raw_spinlock_t irq_lock[BCM2835_NUM_BANKS];

};



/* pins are just named GPIO0..GPIO53 */
@@ -461,10 +461,10 @@ static void bcm2835_gpio_irq_enable(struct irq_data *data) 
	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)
@@ -476,12 +476,12 @@ static void bcm2835_gpio_irq_disable(struct irq_data *data) 
	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,
@@ -584,7 +584,7 @@ static int bcm2835_gpio_irq_set_type(struct irq_data *data, unsigned int type) 
	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);
@@ -596,7 +596,7 @@ static int bcm2835_gpio_irq_set_type(struct irq_data *data, unsigned int type) 
	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;

}
@@ -1047,7 +1047,7 @@ static int bcm2835_pinctrl_probe(struct platform_device *pdev) 
		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);