powerpc: fsl_pci: Add forced PCI Agent enumeration

The following commit prevents the MPC8548E on the XPedite5200 PrPMC
module from enumerating its PCI/PCI-X bus:

    powerpc/fsl-pci: use 'Header Type' to identify PCIE mode

The previous patch prevents any Freescale PCI-X bridge from enumerating
the bus, if it is hardware strapped into Agent mode.

In PCI-X, the Host is responsible for driving the PCI-X initialization
pattern to devices on the bus, so that they know whether to operate in
conventional PCI or PCI-X mode as well as what the bus timing will be.
For a PCI-X PrPMC, the pattern is driven by the mezzanine carrier it is
installed onto. Therefore, PrPMCs are PCI-X Agents, but one per system
may still enumerate the bus.

This patch causes the device node of any PCI/PCI-X bridge strapped into
Agent mode to be checked for the fsl,pci-agent-force-enum property. If
the property is present in the node, the bridge will be allowed to
enumerate the bus.

Cc: Minghuan Lian <Minghuan.Lian@freescale.com>
Signed-off-by: NAaron Sierra <asierra@xes-inc.com>
Signed-off-by: NScott Wood <scottwood@freescale.com>

Documentation/devicetree/bindings/pci/fsl,pci.txt

+* Bus Enumeration by Freescale PCI-X Agent
+
+Typically any Freescale PCI-X bridge hardware strapped into Agent mode
+is prevented from enumerating the bus. The PrPMC form-factor requires
+all mezzanines to be PCI-X Agents, but one per system may still
+enumerate the bus.
+
+The property defined below will allow a PCI-X bridge to be used for bus
+enumeration despite being strapped into Agent mode.
+
+Required properties:
+- fsl,pci-agent-force-enum : There is no value associated with this
+  property. The property itself is treated as a boolean.
+
+Example:
+
+	/* PCI-X bridge known to be PrPMC Monarch */
+	pci0: pci@ef008000 {
+		fsl,pci-agent-force-enum;
+		#interrupt-cells = <1>;
+		#size-cells = <2>;
+		#address-cells = <3>;
+		compatible = "fsl,mpc8540-pcix", "fsl,mpc8540-pci";
+		device_type = "pci";
+		...
+		...
+	};

arch/powerpc/sysdev/fsl_pci.c

@@ -522,7 +522,8 @@ int fsl_add_bridge(struct platform_device *pdev, int is_primary)
 	} else {
 		/* For PCI read PROG to identify controller mode */
 		early_read_config_byte(hose, 0, 0, PCI_CLASS_PROG, &progif);
-		if ((progif & 1) == 1)
+		if ((progif & 1) &&
+		    !of_property_read_bool(dev, "fsl,pci-agent-force-enum"))
 			goto no_bridge;
 	}