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pinctrl: bcm2835: Use raw spinlock for RT compatibility 

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>
hifive-unleashed-5.1
Lukas Wunner 2018-10-27 10:15:33 +02:00 committed by Linus Walleij
parent 623f788d0e
commit 3c7b30f704
1 changed files with 8 additions and 8 deletions
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16
drivers/pinctrl/bcm/pinctrl-bcm2835.c
View File

@ -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);