net/fsl_pq_mdio: check TBI address for consistency with mapped range

When configuring the MDIO subsystem it is also necessary to configure
the TBI register. Make sure the TBI is contained within the mapped
register range in order to:
a) make sure the address is computed correctly
b) make users aware that we're actually accessing that register

In case of error, print a message but continue anyway.

Signed-off-by: Gerlando Falauto <gerlando.falauto@keymile.com>
Cc: Timur Tabi <timur@tabi.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/freescale/fsl_pq_mdio.c

@@ -445,6 +445,16 @@ static int fsl_pq_mdio_probe(struct platform_device *pdev)
 
 			tbipa = data->get_tbipa(priv->map);
 
+			/*
+			 * Add consistency check to make sure TBI is contained
+			 * within the mapped range (not because we would get a
+			 * segfault, rather to catch bugs in computing TBI
+			 * address). Print error message but continue anyway.
+			 */
+			if ((void *)tbipa > priv->map + resource_size(&res) - 4)
+				dev_err(&pdev->dev, "invalid register map (should be at least 0x%04x to contain TBI address)\n",
+					((void *)tbipa - priv->map) + 4);
+
 			iowrite32be(be32_to_cpup(prop), tbipa);
 		}
 	}