ARM: s3c: irq-s3c24xx: Fix return value check for s3c24xx_init_intc()

The s3c24xx_init_intc() returns an error pointer upon failure, not NULL.
let's add an error pointer check in s3c24xx_handle_irq.

s3c_intc[0] is not NULL or ERR, we can simplify the code.

Fixes: 1f629b7a3c ("ARM: S3C24XX: transform irq handling into a declarative form")
Signed-off-by: Jackie Liu <liuyun01@kylinos.cn>
Link: https://lore.kernel.org/r/20210901123557.1043953-1-liu.yun@linux.dev
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>

arch/arm/mach-s3c/irq-s3c24xx.c

@@ -361,11 +361,25 @@ static inline int s3c24xx_handle_intc(struct s3c_irq_intc *intc,
 static asmlinkage void __exception_irq_entry s3c24xx_handle_irq(struct pt_regs *regs)
 {
 	do {
-		if (likely(s3c_intc[0]))
-			if (s3c24xx_handle_intc(s3c_intc[0], regs, 0))
-				continue;
+		/*
+		 * For platform based machines, neither ERR nor NULL can happen here.
+		 * The s3c24xx_handle_irq() will be set as IRQ handler iff this succeeds:
+		 *
+		 *    s3c_intc[0] = s3c24xx_init_intc()
+		 *
+		 * If this fails, the next calls to s3c24xx_init_intc() won't be executed.
+		 *
+		 * For DT machine, s3c_init_intc_of() could set the IRQ handler without
+		 * setting s3c_intc[0] only if it was called with num_ctrl=0. There is no
+		 * such code path, so again the s3c_intc[0] will have a valid pointer if
+		 * set_handle_irq() is called.
+		 *
+		 * Therefore in s3c24xx_handle_irq(), the s3c_intc[0] is always something.
+		 */
+		if (s3c24xx_handle_intc(s3c_intc[0], regs, 0))
+			continue;
 
-		if (s3c_intc[2])
+		if (!IS_ERR_OR_NULL(s3c_intc[2]))
 			if (s3c24xx_handle_intc(s3c_intc[2], regs, 64))
 				continue;