[PATCH v2 1/2] of: platform: Make sure bus only devices get probed

[Saravana Kannan <saravanak@google.com>]

fw_devlink could end up creating device links for bus only devices.
However, bus only devices don't get probed and can block probe() or
sync_state() [1] call backs of other devices. To avoid this, set up
these devices to get probed by the simple-pm-bus.

[1] - https://lore.kernel.org/lkml/CAPDyKFo9Bxremkb1dDrr4OcXSpE0keVze94Cm=zrkOVxHHxBmQ@mail.gmail.com/
Signed-off-by: Saravana Kannan <saravanak@google.com>
Tested-by: Saravana Kannan <saravanak@google.com>
---
 drivers/of/platform.c | 45 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

diff --git a/drivers/of/platform.c b/drivers/of/platform.c
index 74afbb7a4f5e..b010e2310131 100644
--- a/drivers/of/platform.c
+++ b/drivers/of/platform.c
@@ -97,6 +97,48 @@ static void of_device_make_bus_id(struct device *dev)
 	}
 }
 
+/**
+ * of_match_only_simple_bus - Check if a device node is only a simple bus
+ * @np: device node to check
+ *
+ * A simple bus in this context is defined as a transparent bus whose child
+ * devices are automatically populated but has no hardware specific
+ * functionality.
+ *
+ * Returns true if the device node is only a simple bus and can never match
+ * with any other specific driver.  Otherwise, returns false.
+ */
+static bool of_match_only_simple_bus(struct device_node *np)
+{
+	/* List of buses that don't have an explicit driver. */
+	static const char * const of_simple_bus_table[] = {
+		"simple-bus",
+		"simple-mfd",
+		"isa",
+		"arm,amba-bus",
+	};
+	const char *cp;
+	struct property *prop;
+	int i;
+
+	prop = of_find_property(np, "compatible", NULL);
+	for (cp = of_prop_next_string(prop, NULL); cp;
+	     cp = of_prop_next_string(prop, cp)) {
+		bool match = false;
+		const char *bus = of_simple_bus_table[i];
+
+		for (i = 0; i < ARRAY_SIZE(of_simple_bus_table); i++)
+			if (!of_compat_cmp(cp, bus, strlen(bus))) {
+				match = true;
+				break;
+			}
+		if (!match)
+			return false;
+	}
+
+	return true;
+}
+
 /**
  * of_device_alloc - Allocate and initialize an of_device
  * @np: device node to assign to device
@@ -143,6 +185,9 @@ struct platform_device *of_device_alloc(struct device_node *np,
 	dev->dev.fwnode = &np->fwnode;
 	dev->dev.parent = parent ? : &platform_bus;
 
+	if (of_match_only_simple_bus(np))
+		dev->driver_override = "simple-pm-bus";
+
 	if (bus_id)
 		dev_set_name(&dev->dev, "%s", bus_id);
 	else
-- 
2.33.0.153.gba50c8fa24-goog