gpio: tqmx86: fix broken IRQ_TYPE_EDGE_BOTH interrupt type

The TQMx86 GPIO controller only supports falling and rising edge
triggers, but not both. Fix this by implementing a software both-edge
mode that toggles the edge type after every interrupt.

Fixes: b868db94a6a7 ("gpio: tqmx86: Add GPIO from for this IO controller")
Co-developed-by: Gregor Herburger <[e-mail]>
Signed-off-by: Gregor Herburger <[e-mail]>
Signed-off-by: Matthias Schiffer <[e-mail]>
Link: https://lore.kernel.org/r/515324f04[e-mail]
Signed-off-by: Bartosz Golaszewski <[e-mail]>

drivers/gpio/gpio-tqmx86.c

···
 #define TQMX86_GPII_NONE	0
 #define TQMX86_GPII_FALLING	BIT(0)
 #define TQMX86_GPII_RISING	BIT(1)
+/* Stored in irq_type as a trigger type, but not actually valid as a register
+ * value, so the name doesn't use "GPII"
+ */
+#define TQMX86_INT_BOTH		(BIT(0) | BIT(1))
 #define TQMX86_GPII_MASK	(BIT(0) | BIT(1))
 #define TQMX86_GPII_BITS	2
 /* Stored in irq_type with GPII bits */
···
 {
 	u8 type = TQMX86_GPII_NONE, gpiic;
 
-	if (gpio->irq_type[offset] & TQMX86_INT_UNMASKED)
+	if (gpio->irq_type[offset] & TQMX86_INT_UNMASKED) {
 		type = gpio->irq_type[offset] & TQMX86_GPII_MASK;
+
+		if (type == TQMX86_INT_BOTH)
+			type = tqmx86_gpio_get(&gpio->chip, offset + TQMX86_NGPO)
+				? TQMX86_GPII_FALLING
+				: TQMX86_GPII_RISING;
+	}
 
 	gpiic = tqmx86_gpio_read(gpio, TQMX86_GPIIC);
 	gpiic &= ~(TQMX86_GPII_MASK << (offset * TQMX86_GPII_BITS));
···
 		new_type = TQMX86_GPII_FALLING;
 		break;
 	case IRQ_TYPE_EDGE_BOTH:
-		new_type = TQMX86_GPII_FALLING | TQMX86_GPII_RISING;
+		new_type = TQMX86_INT_BOTH;
 		break;
 	default:
 		return -EINVAL; /* not supported */
···
 	struct gpio_chip *chip = irq_desc_get_handler_data(desc);
 	struct tqmx86_gpio_data *gpio = gpiochip_get_data(chip);
 	struct irq_chip *irq_chip = irq_desc_get_chip(desc);
-	unsigned long irq_bits;
-	int i = 0;
+	unsigned long irq_bits, flags;
+	int i;
 	u8 irq_status;
 
 	chained_irq_enter(irq_chip, desc);
···
 	tqmx86_gpio_write(gpio, irq_status, TQMX86_GPIIS);
 
 	irq_bits = irq_status;
+
+	raw_spin_lock_irqsave(&gpio->spinlock, flags);
+	for_each_set_bit(i, &irq_bits, TQMX86_NGPI) {
+		/*
+		 * Edge-both triggers are implemented by flipping the edge
+		 * trigger after each interrupt, as the controller only supports
+		 * either rising or falling edge triggers, but not both.
+		 *
+		 * Internally, the TQMx86 GPIO controller has separate status
+		 * registers for rising and falling edge interrupts. GPIIC
+		 * configures which bits from which register are visible in the
+		 * interrupt status register GPIIS and defines what triggers the
+		 * parent IRQ line. Writing to GPIIS always clears both rising
+		 * and falling interrupt flags internally, regardless of the
+		 * currently configured trigger.
+		 *
+		 * In consequence, we can cleanly implement the edge-both
+		 * trigger in software by first clearing the interrupt and then
+		 * setting the new trigger based on the current GPIO input in
+		 * tqmx86_gpio_irq_config() - even if an edge arrives between
+		 * reading the input and setting the trigger, we will have a new
+		 * interrupt pending.
+		 */
+		if ((gpio->irq_type[i] & TQMX86_GPII_MASK) == TQMX86_INT_BOTH)
+			tqmx86_gpio_irq_config(gpio, i);
+	}
+	raw_spin_unlock_irqrestore(&gpio->spinlock, flags);
+
 	for_each_set_bit(i, &irq_bits, TQMX86_NGPI)
 		generic_handle_domain_irq(gpio->chip.irq.domain,
 					  i + TQMX86_NGPO);