mailbox: mailbox-test: fix null pointer if no mmio

commit 6899b4f7 upstream.

Fix null pointer issue if resource_size is called with no ioresource.
Signed-off-by: Ludovic Barre <ludovic.barre@st.com>
Signed-off-by: Fabien Dessenne <fabien.dessenne@st.com>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/mailbox/mailbox-test.c

@@ -363,22 +363,24 @@ static int mbox_test_probe(struct platform_device *pdev)
 
 	/* It's okay for MMIO to be NULL */
 	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
-	size = resource_size(res);
 	tdev->tx_mmio = devm_ioremap_resource(&pdev->dev, res);
-	if (PTR_ERR(tdev->tx_mmio) == -EBUSY)
+	if (PTR_ERR(tdev->tx_mmio) == -EBUSY) {
 		/* if reserved area in SRAM, try just ioremap */
+		size = resource_size(res);
 		tdev->tx_mmio = devm_ioremap(&pdev->dev, res->start, size);
-	else if (IS_ERR(tdev->tx_mmio))
+	} else if (IS_ERR(tdev->tx_mmio)) {
 		tdev->tx_mmio = NULL;
+	}
 
 	/* If specified, second reg entry is Rx MMIO */
 	res = platform_get_resource(pdev, IORESOURCE_MEM, 1);
-	size = resource_size(res);
 	tdev->rx_mmio = devm_ioremap_resource(&pdev->dev, res);
-	if (PTR_ERR(tdev->rx_mmio) == -EBUSY)
+	if (PTR_ERR(tdev->rx_mmio) == -EBUSY) {
+		size = resource_size(res);
 		tdev->rx_mmio = devm_ioremap(&pdev->dev, res->start, size);
-	else if (IS_ERR(tdev->rx_mmio))
+	} else if (IS_ERR(tdev->rx_mmio)) {
 		tdev->rx_mmio = tdev->tx_mmio;
+	}
 
 	tdev->tx_channel = mbox_test_request_channel(pdev, "tx");
 	tdev->rx_channel = mbox_test_request_channel(pdev, "rx");