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>

diff --git a/drivers/pinctrl/bcm/pinctrl-bcm2835.c b/drivers/pinctrl/bcm/pinctrl-bcm2835.c
index fa530913a2c8fc73c37a9b668447f1058d99815a..08925d24180b08f976137a60b6e0533b4340e636 100644 (file)
--- a/drivers/pinctrl/bcm/pinctrl-bcm2835.c
+++ b/drivers/pinctrl/bcm/pinctrl-bcm2835.c
@@ -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);