gpio: 104-idi-48: make use of raw_spinlock variants

The 104-idi-48 gpio driver currently implements an irq_chip for handling
interrupts; due to how irq_chip handling is done, it's necessary for the
irq_chip methods to be invoked from hardirq context, even on a a
real-time kernel.  Because the spinlock_t type becomes a "sleeping"
spinlock w/ RT kernels, it is not suitable to be used with irq_chips.

A quick audit of the operations under the lock reveal that they do only
minimal, bounded work, and are therefore safe to do under a raw spinlock.

Signed-off-by: Julia Cartwright <julia@ni.com>
Acked-by: William Breathitt Gray <vilhelm.gray@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpio-104-idi-48.c

@@ -51,7 +51,7 @@ MODULE_PARM_DESC(irq, "ACCES 104-IDI-48 interrupt line numbers");
  */
 struct idi_48_gpio {
 	struct gpio_chip chip;
-	spinlock_t lock;
+	raw_spinlock_t lock;
 	spinlock_t ack_lock;
 	unsigned char irq_mask[6];
 	unsigned base;
@@ -112,11 +112,12 @@ static void idi_48_irq_mask(struct irq_data *data)
 			if (!idi48gpio->irq_mask[boundary]) {
 				idi48gpio->cos_enb &= ~BIT(boundary);
 
-				spin_lock_irqsave(&idi48gpio->lock, flags);
+				raw_spin_lock_irqsave(&idi48gpio->lock, flags);
 
 				outb(idi48gpio->cos_enb, idi48gpio->base + 7);
 
-				spin_unlock_irqrestore(&idi48gpio->lock, flags);
+				raw_spin_unlock_irqrestore(&idi48gpio->lock,
+						           flags);
 			}
 
 			return;
@@ -145,11 +146,12 @@ static void idi_48_irq_unmask(struct irq_data *data)
 			if (!prev_irq_mask) {
 				idi48gpio->cos_enb |= BIT(boundary);
 
-				spin_lock_irqsave(&idi48gpio->lock, flags);
+				raw_spin_lock_irqsave(&idi48gpio->lock, flags);
 
 				outb(idi48gpio->cos_enb, idi48gpio->base + 7);
 
-				spin_unlock_irqrestore(&idi48gpio->lock, flags);
+				raw_spin_unlock_irqrestore(&idi48gpio->lock,
+						           flags);
 			}
 
 			return;
@@ -186,11 +188,11 @@ static irqreturn_t idi_48_irq_handler(int irq, void *dev_id)
 
 	spin_lock(&idi48gpio->ack_lock);
 
-	spin_lock(&idi48gpio->lock);
+	raw_spin_lock(&idi48gpio->lock);
 
 	cos_status = inb(idi48gpio->base + 7);
 
-	spin_unlock(&idi48gpio->lock);
+	raw_spin_unlock(&idi48gpio->lock);
 
 	/* IRQ Status (bit 6) is active low (0 = IRQ generated by device) */
 	if (cos_status & BIT(6)) {
@@ -256,7 +258,7 @@ static int idi_48_probe(struct device *dev, unsigned int id)
 	idi48gpio->chip.get = idi_48_gpio_get;
 	idi48gpio->base = base[id];
 
-	spin_lock_init(&idi48gpio->lock);
+	raw_spin_lock_init(&idi48gpio->lock);
 	spin_lock_init(&idi48gpio->ack_lock);
 
 	err = devm_gpiochip_add_data(dev, &idi48gpio->chip, idi48gpio);