ARM: 7377/1: vic: re-read status register before dispatching each IRQ handler

handle_IRQ may briefly cause interrupts to be re-enabled during soft IRQ
processing on the exit path, leading to nested handling of VIC interrupts.

Since the current code does not re-read the VIC_IRQ_STATUS register, this
can lead to multiple invocations of the same interrupt handler and
spurious interrupts to be reported.

This patch changes the VIC interrupt dispatching code to re-read the
status register each time, avoiding duplicate invocations of the same
handler.

Acked-and-Tested-by: H Hartley Sweeten <hsweeten@visionengravers.com>

Reviewed-by: Jamie Iles <jamie@jamieiles.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/common/vic.c

@@ -427,19 +427,18 @@ int __init vic_of_init(struct device_node *node, struct device_node *parent)
 
 /*
  * Handle each interrupt in a single VIC.  Returns non-zero if we've
- * handled at least one interrupt.  This does a single read of the
- * status register and handles all interrupts in order from LSB first.
+ * handled at least one interrupt.  This reads the status register
+ * before handling each interrupt, which is necessary given that
+ * handle_IRQ may briefly re-enable interrupts for soft IRQ handling.
  */
 static int handle_one_vic(struct vic_device *vic, struct pt_regs *regs)
 {
 	u32 stat, irq;
 	int handled = 0;
 
-	stat = readl_relaxed(vic->base + VIC_IRQ_STATUS);
-	while (stat) {
+	while ((stat = readl_relaxed(vic->base + VIC_IRQ_STATUS))) {
 		irq = ffs(stat) - 1;
 		handle_IRQ(irq_find_mapping(vic->domain, irq), regs);
-		stat &= ~(1 << irq);
 		handled = 1;
 	}