diff --git a/drivers/ata/pata_octeon_cf.c b/drivers/ata/pata_octeon_cf.c
index ff2e57f3b597..e73bef3093d2 100644
--- a/drivers/ata/pata_octeon_cf.c
+++ b/drivers/ata/pata_octeon_cf.c
@@ -926,7 +926,7 @@ static int octeon_cf_probe(struct platform_device *pdev)
 			goto free_cf_port;
 		}
 		cs1 = devm_ioremap_nocache(&pdev->dev, res_cs1->start,
-					   res_cs1->end - res_cs1->start + 1);
+					   resource_size(res_cs1));
 
 		if (!cs1)
 			goto free_cf_port;