gpio: 104-idi-48: Clear pending interrupt once in IRQ handler

Performing a read operation on the IRQ Status register will clear the
IRQ latch. Since a read operation on the IRQ Status register must be
performed in the IRQ handler in order to determine if the IRQ was in
fact generated by the device, the IRQ latch is consequently cleared by
the IRQ handler. A spinlock is used to guarantee that each IRQ is
serviced in the order it was received.
Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>

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

@@ -36,6 +36,7 @@ MODULE_PARM_DESC(idi_48_irq, "ACCES 104-IDI-48 interrupt line number");
  * struct idi_48_gpio - GPIO device private data structure
  * @chip:	instance of the gpio_chip
  * @lock:	synchronization lock to prevent I/O race conditions
+ * @ack_lock:	synchronization lock to prevent IRQ handler race conditions
  * @irq_mask:	input bits affected by interrupts
  * @base:	base port address of the GPIO device
  * @extent:	extent of port address region of the GPIO device
@@ -45,6 +46,7 @@ MODULE_PARM_DESC(idi_48_irq, "ACCES 104-IDI-48 interrupt line number");
 struct idi_48_gpio {
 	struct gpio_chip chip;
 	spinlock_t lock;
+	spinlock_t ack_lock;
 	unsigned char irq_mask[6];
 	unsigned base;
 	unsigned extent;
@@ -89,15 +91,6 @@ static int idi_48_gpio_get(struct gpio_chip *chip, unsigned offset)
 
 static void idi_48_irq_ack(struct irq_data *data)
 {
-	struct gpio_chip *chip = irq_data_get_irq_chip_data(data);
-	struct idi_48_gpio *const idi48gpio = to_idi48gpio(chip);
-	unsigned long flags;
-
-	spin_lock_irqsave(&idi48gpio->lock, flags);
-
-	inb(idi48gpio->base + 7);
-
-	spin_unlock_irqrestore(&idi48gpio->lock, flags);
 }
 
 static void idi_48_irq_mask(struct irq_data *data)
@@ -192,6 +185,8 @@ static irqreturn_t idi_48_irq_handler(int irq, void *dev_id)
 	unsigned long gpio;
 	struct gpio_chip *const chip = &idi48gpio->chip;
 
+	spin_lock(&idi48gpio->ack_lock);
+
 	spin_lock(&idi48gpio->lock);
 
 	cos_status = inb(idi48gpio->base + 7);
@@ -199,8 +194,10 @@ static irqreturn_t idi_48_irq_handler(int irq, void *dev_id)
 	spin_unlock(&idi48gpio->lock);
 
 	/* IRQ Status (bit 6) is active low (0 = IRQ generated by device) */
-	if (cos_status & BIT(6))
+	if (cos_status & BIT(6)) {
+		spin_unlock(&idi48gpio->ack_lock);
 		return IRQ_NONE;
+	}
 
 	/* Bit 0-5 indicate which Change-Of-State boundary triggered the IRQ */
 	cos_status &= 0x3F;
@@ -216,6 +213,8 @@ static irqreturn_t idi_48_irq_handler(int irq, void *dev_id)
 		}
 	}
 
+	spin_unlock(&idi48gpio->ack_lock);
+
 	return IRQ_HANDLED;
 }