PCI: designware: Ensure ATU is enabled before IO/conf space accesses

Read back the ATU CR2 register to ensure ATU programming is effective
before any subsequent I/O or config space accesses.

Without this, PCI device enumeration is unreliable.

[bhelgaas: changelog, comment]
Signed-off-by: NStanimir Varbanov <stanimir.varbanov@linaro.org>
Signed-off-by: NBjorn Helgaas <bhelgaas@google.com>
Acked-by: NPratyush Anand <pratyush.anand@gmail.com>

drivers/pci/host/pcie-designware.c

@@ -154,6 +154,8 @@ static int dw_pcie_wr_own_conf(struct pcie_port *pp, int where, int size,
 static void dw_pcie_prog_outbound_atu(struct pcie_port *pp, int index,
 		int type, u64 cpu_addr, u64 pci_addr, u32 size)
 {
+	u32 val;
+
 	dw_pcie_writel_rc(pp, PCIE_ATU_REGION_OUTBOUND | index,
 			  PCIE_ATU_VIEWPORT);
 	dw_pcie_writel_rc(pp, lower_32_bits(cpu_addr), PCIE_ATU_LOWER_BASE);
@@ -164,6 +166,12 @@ static void dw_pcie_prog_outbound_atu(struct pcie_port *pp, int index,
 	dw_pcie_writel_rc(pp, upper_32_bits(pci_addr), PCIE_ATU_UPPER_TARGET);
 	dw_pcie_writel_rc(pp, type, PCIE_ATU_CR1);
 	dw_pcie_writel_rc(pp, PCIE_ATU_ENABLE, PCIE_ATU_CR2);
+
+	/*
+	 * Make sure ATU enable takes effect before any subsequent config
+	 * and I/O accesses.
+	 */
+	dw_pcie_readl_rc(pp, PCIE_ATU_CR2, &val);
 }
 
 static struct irq_chip dw_msi_irq_chip = {