static int unimac_mdio_read(struct mii_bus *bus, int phy_id, int reg)
{
	struct unimac_mdio_priv *priv = bus->priv;
	int ret;
	u32 cmd;

	/* Prepare the read operation */
	cmd = MDIO_RD | (phy_id << MDIO_PMD_SHIFT) | (reg << MDIO_REG_SHIFT);
	unimac_mdio_writel(priv, cmd, MDIO_CMD);

	/* Start MDIO transaction */
	unimac_mdio_start(priv);

	ret = priv->wait_func(priv->wait_func_data);
	if (ret)
		return ret;

	cmd = unimac_mdio_readl(priv, MDIO_CMD);

	/* Some broken devices are known not to release the line during
	 * turn-around, e.g: Broadcom BCM53125 external switches, so check for
	 * that condition here and ignore the MDIO controller read failure
	 * indication.
	 */
	if (!(bus->phy_ignore_ta_mask & 1 << phy_id) && (cmd & MDIO_READ_FAIL))
		return -EIO;

	return cmd & 0xffff;
}

The product dereferences a pointer that it expects to be valid but is NULL.