irqchip: loongson-liointc: Workaround LPC IRQ Errata

The 1.0 version of that controller has a bug that status bit
of LPC IRQ sometimes doesn't get set correctly.

So we can always blame LPC IRQ when spurious interrupt happens
at the parent interrupt line which LPC IRQ supposed to route
to.
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Co-developed-by: Huacai Chen <chenhc@lemote.com>
Signed-off-by: Huacai Chen <chenhc@lemote.com>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

drivers/irqchip/irq-loongson-liointc.c

@@ -32,6 +32,8 @@
 
 #define LIOINTC_SHIFT_INTx	4
 
+#define LIOINTC_ERRATA_IRQ	10
+
 struct liointc_handler_data {
 	struct liointc_priv	*priv;
 	u32			parent_int_map;
@@ -41,6 +43,7 @@ struct liointc_priv {
 	struct irq_chip_generic		*gc;
 	struct liointc_handler_data	handler[LIOINTC_NUM_PARENT];
 	u8				map_cache[LIOINTC_CHIP_IRQ];
+	bool				has_lpc_irq_errata;
 };
 
 static void liointc_chained_handle_irq(struct irq_desc *desc)
@@ -54,8 +57,15 @@ static void liointc_chained_handle_irq(struct irq_desc *desc)
 
 	pending = readl(gc->reg_base + LIOINTC_REG_INTC_STATUS);
 
-	if (!pending)
-		spurious_interrupt();
+	if (!pending) {
+		/* Always blame LPC IRQ if we have that bug */
+		if (handler->priv->has_lpc_irq_errata &&
+			(handler->parent_int_map & ~gc->mask_cache &
+			BIT(LIOINTC_ERRATA_IRQ)))
+			pending = BIT(LIOINTC_ERRATA_IRQ);
+		else
+			spurious_interrupt();
+	}
 
 	while (pending) {
 		int bit = __ffs(pending);