irqchip: Ingenic: Add process for more than one irq at the same time.

Add process for the situation that more than one irq is coming to
a single chip at the same time. The original code will only respond
to the lowest setted bit in JZ_REG_INTC_PENDING, and then exit the
interrupt dispatch function. After exiting the interrupt dispatch
function, since the second interrupt has not yet responded, the
interrupt dispatch function is again entered to process the second
interrupt. This creates additional unnecessary overhead, and the
more interrupts that occur at the same time, the more overhead is
added. The improved method in this patch is to check whether there
are still unresponsive interrupts after processing the lowest
setted bit interrupt. If there are any, the processing will be
processed according to the bit in JZ_REG_INTC_PENDING, and the
interrupt dispatch function will be exited until all processing
is completed.
Signed-off-by: Zhou Yanjie <zhouyanjie@zoho.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Paul Cercueil <paul@crapouillou.net>
Link: https://lore.kernel.org/r/1570015525-27018-6-git-send-email-zhouyanjie@zoho.com

drivers/irqchip/irq-ingenic.c

 // SPDX-License-Identifier: GPL-2.0-or-later
 /*
  *  Copyright (C) 2009-2010, Lars-Peter Clausen <lars@metafoo.de>
- *  JZ4740 platform IRQ support
+ *  Ingenic XBurst platform IRQ support
  */
 
 #include <linux/errno.h>
@@ -37,18 +37,23 @@ static irqreturn_t intc_cascade(int irq, void *data)
 	struct ingenic_intc_data *intc = irq_get_handler_data(irq);
 	struct irq_domain *domain = intc->domain;
 	struct irq_chip_generic *gc;
-	uint32_t irq_reg;
+	uint32_t pending;
 	unsigned i;
 
 	for (i = 0; i < intc->num_chips; i++) {
 		gc = irq_get_domain_generic_chip(domain, i * 32);
 
-		irq_reg = irq_reg_readl(gc, JZ_REG_INTC_PENDING);
-		if (!irq_reg)
+		pending = irq_reg_readl(gc, JZ_REG_INTC_PENDING);
+		if (!pending)
 			continue;
 
-		irq = irq_find_mapping(domain, __fls(irq_reg) + (i * 32));
-		generic_handle_irq(irq);
+		while (pending) {
+			int bit = __fls(pending);
+
+			irq = irq_find_mapping(domain, bit + (i * 32));
+			generic_handle_irq(irq);
+			pending &= ~BIT(bit);
+		}
 	}
 
 	return IRQ_HANDLED;