of/pci: Add of_pci_check_probe_only to parse "linux,pci-probe-only"

Both pci-host-generic and Pseries parse the "linux,pci-probe-only" property
to engage the PCI_PROBE_ONLY mode, and both have a subtle bug that can be
triggered if the property has no parameter.

Provide a generic, safe implementation that can be used by both.

[bhelgaas: fold in #include <asm-generic/pci-bridge.h>]
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Rob Herring <robh@kernel.org>

drivers/of/of_pci.c

@@ -5,6 +5,7 @@
 #include <linux/of_device.h>
 #include <linux/of_pci.h>
 #include <linux/slab.h>
+#include <asm-generic/pci-bridge.h>
 
 static inline int __of_pci_pci_compare(struct device_node *node,
 				       unsigned int data)
@@ -117,6 +118,31 @@ int of_get_pci_domain_nr(struct device_node *node)
 }
 EXPORT_SYMBOL_GPL(of_get_pci_domain_nr);
 
+/**
+ * of_pci_check_probe_only - Setup probe only mode if linux,pci-probe-only
+ *                           is present and valid
+ */
+void of_pci_check_probe_only(void)
+{
+	u32 val;
+	int ret;
+
+	ret = of_property_read_u32(of_chosen, "linux,pci-probe-only", &val);
+	if (ret) {
+		if (ret == -ENODATA || ret == -EOVERFLOW)
+			pr_warn("linux,pci-probe-only without valid value, ignoring\n");
+		return;
+	}
+
+	if (val)
+		pci_add_flags(PCI_PROBE_ONLY);
+	else
+		pci_clear_flags(PCI_PROBE_ONLY);
+
+	pr_info("PCI: PROBE_ONLY %sabled\n", val ? "en" : "dis");
+}
+EXPORT_SYMBOL_GPL(of_pci_check_probe_only);
+
 /**
  * of_pci_dma_configure - Setup DMA configuration
  * @dev: ptr to pci_dev struct of the PCI device

include/linux/of_pci.h

@@ -17,6 +17,7 @@ int of_irq_parse_and_map_pci(const struct pci_dev *dev, u8 slot, u8 pin);
 int of_pci_parse_bus_range(struct device_node *node, struct resource *res);
 int of_get_pci_domain_nr(struct device_node *node);
 void of_pci_dma_configure(struct pci_dev *pci_dev);
+void of_pci_check_probe_only(void);
 #else
 static inline int of_irq_parse_pci(const struct pci_dev *pdev, struct of_phandle_args *out_irq)
 {
@@ -53,6 +54,8 @@ of_get_pci_domain_nr(struct device_node *node)
 }
 
 static inline void of_pci_dma_configure(struct pci_dev *pci_dev) { }
+
+static inline void of_pci_check_probe_only(void) { }
 #endif
 
 #if defined(CONFIG_OF_ADDRESS)