ARM: versatile: add DT based PCI detection

Disable the Versatile PCI DT node when no PCI backplane is detected. This
will prevent the Versatile PCI driver from probing when PCI is not
populated.

Signed-off-by: Rob Herring <robh@kernel.org>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

arch/arm/mach-versatile/versatile_dt.c

@@ -22,15 +22,65 @@
  */
 
 #include <linux/init.h>
+#include <linux/io.h>
+#include <linux/of.h>
+#include <linux/of_address.h>
 #include <linux/of_irq.h>
 #include <linux/of_platform.h>
+#include <linux/slab.h>
 #include <asm/mach-types.h>
 #include <asm/mach/arch.h>
 
 #include "core.h"
 
+#define VERSATILE_SYS_PCICTL_OFFSET           0x44
+static void __iomem *versatile_sys_base;
+
+static void __init versatile_dt_pci_init(void)
+{
+	u32 val;
+	struct device_node *np;
+	struct property *newprop;
+
+	np = of_find_compatible_node(NULL, NULL, "arm,versatile-pci");
+	if (!np)
+		return;
+
+	/* Check if PCI backplane is detected */
+	val = readl(versatile_sys_base + VERSATILE_SYS_PCICTL_OFFSET);
+	if (val & 1) {
+		/*
+		 * Enable PCI accesses. Note that the documentaton is
+		 * inconsistent whether or not this is needed, but the old
+		 * driver had it so we will keep it.
+		 */
+		writel(1, versatile_sys_base + VERSATILE_SYS_PCICTL_OFFSET);
+		return;
+	}
+
+	newprop = kzalloc(sizeof(*newprop), GFP_KERNEL);
+	if (!newprop)
+		return;
+
+	newprop->name = kstrdup("status", GFP_KERNEL);
+	newprop->value = kstrdup("disabled", GFP_KERNEL);
+	newprop->length = sizeof("disabled");
+	of_update_property(np, newprop);
+
+	pr_info("Not plugged into PCI backplane!\n");
+}
+
 static void __init versatile_dt_init(void)
 {
+	struct device_node *np;
+
+	np = of_find_compatible_node(NULL, NULL, "arm,core-module-versatile");
+	if (np)
+		versatile_sys_base = of_iomap(np, 0);
+	WARN_ON(!versatile_sys_base);
+
+	versatile_dt_pci_init();
+
 	of_platform_populate(NULL, of_default_bus_match_table,
 			     versatile_auxdata_lookup, NULL);
 }