gpio: Remove VLA from stmpe driver

The new challenge is to remove VLAs from the kernel
(see https://lkml.org/lkml/2018/3/7/621)

The number of GPIOs on the supported chips is fairly small
so stack allocate to a known upper bound and spit out a warning
if any new chips have more gpios.
Signed-off-by: Laura Abbott <labbott@redhat.com>
Reviewed-by: Phil Reid <preid@electromag.com.au>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpio-stmpe.c

@@ -363,13 +363,15 @@ static struct irq_chip stmpe_gpio_irq_chip = {
 	.irq_set_type		= stmpe_gpio_irq_set_type,
 };
 
+#define MAX_GPIOS 24
+
 static irqreturn_t stmpe_gpio_irq(int irq, void *dev)
 {
 	struct stmpe_gpio *stmpe_gpio = dev;
 	struct stmpe *stmpe = stmpe_gpio->stmpe;
 	u8 statmsbreg;
 	int num_banks = DIV_ROUND_UP(stmpe->num_gpios, 8);
-	u8 status[num_banks];
+	u8 status[DIV_ROUND_UP(MAX_GPIOS, 8)];
 	int ret;
 	int i;
 
@@ -434,6 +436,11 @@ static int stmpe_gpio_probe(struct platform_device *pdev)
 	struct stmpe_gpio *stmpe_gpio;
 	int ret, irq;
 
+	if (stmpe->num_gpios > MAX_GPIOS) {
+		dev_err(&pdev->dev, "Need to increase maximum GPIO number\n");
+		return -EINVAL;
+	}
+
 	stmpe_gpio = kzalloc(sizeof(*stmpe_gpio), GFP_KERNEL);
 	if (!stmpe_gpio)
 		return -ENOMEM;