PCI: designware: Add default link up check if sub-driver doesn't override

Add a default DesignWare "link_up" test for use when a sub-driver doesn't
supply its own pcie_host_ops.link_up() method.

[bhelgaas: changelog, split into its own patch]
Signed-off-by: Joao Pinto <jpinto@synopsys.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Pratyush Anand <pratyush.anand@gmail.com>

drivers/pci/host/pcie-designware.c

@@ -70,6 +70,11 @@
 #define PCIE_ATU_FUNC(x)		(((x) & 0x7) << 16)
 #define PCIE_ATU_UPPER_TARGET		0x91C
 
+/* PCIe Port Logic registers */
+#define PLR_OFFSET			0x700
+#define PCIE_PHY_DEBUG_R1		(PLR_OFFSET + 0x2c)
+#define PCIE_PHY_DEBUG_R1_LINK_UP	0x00000010
+
 static struct pci_ops dw_pcie_ops;
 
 int dw_pcie_cfg_read(void __iomem *addr, int size, u32 *val)
@@ -401,10 +406,13 @@ int dw_pcie_wait_for_link(struct pcie_port *pp)
 
 int dw_pcie_link_up(struct pcie_port *pp)
 {
+	u32 val;
+
 	if (pp->ops->link_up)
 		return pp->ops->link_up(pp);
 
-	return 0;
+	val = readl(pp->dbi_base + PCIE_PHY_DEBUG_R1);
+	return val & PCIE_PHY_DEBUG_R1_LINK_UP;
 }
 
 static int dw_pcie_msi_map(struct irq_domain *domain, unsigned int irq,