PCI: dwc: Enable write permission for Class Code, Interrupt Pin updates

dw_pcie_setup_rc() contains fixes to update the Class Code and Interrupt
Pin registers, but the fixes don't actually work because these registers
are read-only.

Enable write permission before updating the Class Code and Interrupt
Pin.

Signed-off-by: Hou Zhiqiang <Zhiqiang.Hou@nxp.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Joao Pinto <jpinto@synopsys.com>
Acked-by: Roy Zang <tie-fei.zang@freescale.com>

drivers/pci/dwc/pcie-designware-host.c

@@ -597,10 +597,12 @@ void dw_pcie_setup_rc(struct pcie_port *pp)
 	dw_pcie_writel_dbi(pci, PCI_BASE_ADDRESS_1, 0x00000000);
 
 	/* setup interrupt pins */
+	dw_pcie_dbi_ro_wr_en(pci);
 	val = dw_pcie_readl_dbi(pci, PCI_INTERRUPT_LINE);
 	val &= 0xffff00ff;
 	val |= 0x00000100;
 	dw_pcie_writel_dbi(pci, PCI_INTERRUPT_LINE, val);
+	dw_pcie_dbi_ro_wr_dis(pci);
 
 	/* setup bus numbers */
 	val = dw_pcie_readl_dbi(pci, PCI_PRIMARY_BUS);
@@ -637,8 +639,12 @@ void dw_pcie_setup_rc(struct pcie_port *pp)
 
 	dw_pcie_wr_own_conf(pp, PCI_BASE_ADDRESS_0, 4, 0);
 
+	/* Enable write permission for the DBI read-only register */
+	dw_pcie_dbi_ro_wr_en(pci);
 	/* program correct class for RC */
 	dw_pcie_wr_own_conf(pp, PCI_CLASS_DEVICE, 2, PCI_CLASS_BRIDGE_PCI);
+	/* Better disable write permission right after the update */
+	dw_pcie_dbi_ro_wr_dis(pci);
 
 	dw_pcie_rd_own_conf(pp, PCIE_LINK_WIDTH_SPEED_CONTROL, 4, &val);
 	val |= PORT_LOGIC_SPEED_CHANGE;