drivers: pci: imx: fix enumeration logic error

By default, the subordinate is set equally to the secondary bus (1) when
the RC boots, and does not alter afterwards.

This means that theoretically, the highest bus reachable downstream is
bus 1.

Force the PCIe RC subordinate to 0xff, otherwise no downstream
devices will be detected behind bus 1 if the booting OS does not allow
enumerating a higher busnr than the subordinate value of the primary
bus.
Signed-off-by: NKoen Vandeputte <koen.vandeputte@ncentric.com>

drivers/pci/pcie_imx.c

@@ -615,6 +615,17 @@ static int imx_pcie_link_up(void)
 
 	imx_pcie_regions_setup();
 
+	/*
+	 * By default, the subordinate is set equally to the secondary
+	 * bus (0x01) when the RC boots.
+	 * This means that theoretically, only bus 1 is reachable from the RC.
+	 * Force the PCIe RC subordinate to 0xff, otherwise no downstream
+	 * devices will be detected if the enumeration is applied strictly.
+	 */
+	tmp = readl(MX6_DBI_ADDR + 0x18);
+	tmp |= (0xff << 16);
+	writel(tmp, MX6_DBI_ADDR + 0x18);
+
 	/*
 	 * FIXME: Force the PCIe RC to Gen1 operation
 	 * The RC must be forced into Gen1 mode before bringing the link