arm/imx/gpio: use fls to find set bits in the irq status register

As in most cases only few irqs are pending using fls is more effective
than looping over all bits.
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

arch/arm/plat-mxc/gpio.c

@@ -154,24 +154,22 @@ static void mxc_flip_edge(struct mxc_gpio_port *port, u32 gpio)
 	__raw_writel(val | (edge << (bit << 1)), reg);
 }
 
-/* handle n interrupts in one status register */
+/* handle 32 interrupts in one status register */
 static void mxc_gpio_irq_handler(struct mxc_gpio_port *port, u32 irq_stat)
 {
-	u32 gpio_irq_no;
+	u32 gpio_irq_no_base = port->virtual_irq_start;
 
-	gpio_irq_no = port->virtual_irq_start;
-	for (; irq_stat != 0; irq_stat >>= 1, gpio_irq_no++) {
-		u32 gpio = irq_to_gpio(gpio_irq_no);
+	while (irq_stat != 0) {
+		int irqoffset = fls(irq_stat) - 1;
 
-		if ((irq_stat & 1) == 0)
-			continue;
+		BUG_ON(!(irq_desc[gpio_irq_no_base + irqoffset].handle_irq));
 
-		BUG_ON(!(irq_desc[gpio_irq_no].handle_irq));
+		if (port->both_edges & (1 << irqoffset))
+			mxc_flip_edge(port, irqoffset);
 
-		if (port->both_edges & (1 << (gpio & 31)))
-			mxc_flip_edge(port, gpio);
+		generic_handle_irq(gpio_irq_no_base + irqoffset);
 
-		generic_handle_irq(gpio_irq_no);
+		irq_stat &= ~(1 << irqoffset);
 	}
 }