PCI: designware: Make "num-lanes" an optional DT property

Currently "num-lanes" is read in dw_pcie_host_init(), but it is only used
if we call dw_pcie_setup_rc() while bringing up the link. If the link has
already been brought up by firmware, we need not call dw_pcie_setup_rc(),
and "num-lanes" is unnecessary.

Only complain about "num-lanes" if we actually need it and we didn't find a
valid value.

[bhelgaas: changelog]
Signed-off-by: Gabriele Paoloni <[e-mail]>
Signed-off-by: Bjorn Helgaas <[e-mail]>

Documentation/devicetree/bindings/pci/designware-pcie.txt

···
 - interrupt-map-mask and interrupt-map: standard PCI properties
 	to define the mapping of the PCIe interface to interrupt
 	numbers.
-- num-lanes: number of lanes to use
 - clocks: Must contain an entry for each entry in clock-names.
 	See ../clocks/clock-bindings.txt for details.
 - clock-names: Must include the following entries:
···
 	- "pcie_bus"
 
 Optional properties:
+- num-lanes: number of lanes to use (this property should be specified unless
+  the link is brought already up in BIOS)
 - reset-gpio: gpio pin number of power good signal
 - bus-range: PCI bus numbers covered (it is recommended for new devicetrees to
   specify this property, to keep backwards compatibility a range of 0x00-0xff

drivers/pci/host/pcie-designware.c

···
 		}
 	}
 
-	if (of_property_read_u32(np, "num-lanes", &pp->lanes)) {
-		dev_err(pp->dev, "Failed to parse the number of lanes\n");
-		return -EINVAL;
-	}
+	ret = of_property_read_u32(np, "num-lanes", &pp->lanes);
+	if (ret)
+		pp->lanes = 0;
 
 	if (IS_ENABLED(CONFIG_PCI_MSI)) {
 		if (!pp->ops->msi_host_init) {
···
 	case 8:
 		val |= PORT_LINK_MODE_8_LANES;
 		break;
+	default:
+		dev_err(pp->dev, "num-lanes %u: invalid value\n", pp->lanes);
+		return;
 	}
 	dw_pcie_writel_rc(pp, val, PCIE_PORT_LINK_CONTROL);