drivers: bus: simple-pm-bus: Add support for probing simple bus only devices

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, probe these
devices using the simple-pm-bus driver.

However, there are instances of devices that are not simple buses (they get
probed by their specific drivers) that also list the "simple-bus" (or other
bus only compatible strings) in their compatible property to automatically
populate their child devices. We still want these devices to get probed by
their specific drivers. So, we make sure this driver only probes devices
that are only buses.

[1] - https://lore.kernel.org/lkml/CAPDyKFo9Bxremkb1dDrr4OcXSpE0keVze94Cm=zrkOVxHHxBmQ@mail.gmail.com/

Fixes: c442a0d1 ("driver core: Set fw_devlink to "permissive" behavior by default")
Cc: stable <stable@vger.kernel.org>
Cc: Rob Herring <robh+dt@kernel.org>
Tested-by: Saravana Kannan <saravanak@google.com>
Tested-by: Ulf Hansson <ulf.hansson@linaro.org>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Tested-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Saravana Kannan <saravanak@google.com>
Link: https://lore.kernel.org/r/20210929000735.585237-2-saravanak@google.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/bus/simple-pm-bus.c

@@ -13,11 +13,36 @@
 #include <linux/platform_device.h>
 #include <linux/pm_runtime.h>
 
-
 static int simple_pm_bus_probe(struct platform_device *pdev)
 {
-	const struct of_dev_auxdata *lookup = dev_get_platdata(&pdev->dev);
-	struct device_node *np = pdev->dev.of_node;
+	const struct device *dev = &pdev->dev;
+	const struct of_dev_auxdata *lookup = dev_get_platdata(dev);
+	struct device_node *np = dev->of_node;
+	const struct of_device_id *match;
+
+	/*
+	 * Allow user to use driver_override to bind this driver to a
+	 * transparent bus device which has a different compatible string
+	 * that's not listed in simple_pm_bus_of_match. We don't want to do any
+	 * of the simple-pm-bus tasks for these devices, so return early.
+	 */
+	if (pdev->driver_override)
+		return 0;
+
+	match = of_match_device(dev->driver->of_match_table, dev);
+	/*
+	 * These are transparent bus devices (not simple-pm-bus matches) that
+	 * have their child nodes populated automatically.  So, don't need to
+	 * do anything more. We only match with the device if this driver is
+	 * the most specific match because we don't want to incorrectly bind to
+	 * a device that has a more specific driver.
+	 */
+	if (match && match->data) {
+		if (of_property_match_string(np, "compatible", match->compatible) == 0)
+			return 0;
+		else
+			return -ENODEV;
+	}
 
 	dev_dbg(&pdev->dev, "%s\n", __func__);
 
@@ -31,14 +56,25 @@ static int simple_pm_bus_probe(struct platform_device *pdev)
 
 static int simple_pm_bus_remove(struct platform_device *pdev)
 {
+	const void *data = of_device_get_match_data(&pdev->dev);
+
+	if (pdev->driver_override || data)
+		return 0;
+
 	dev_dbg(&pdev->dev, "%s\n", __func__);
 
 	pm_runtime_disable(&pdev->dev);
 	return 0;
 }
 
+#define ONLY_BUS	((void *) 1) /* Match if the device is only a bus. */
+
 static const struct of_device_id simple_pm_bus_of_match[] = {
 	{ .compatible = "simple-pm-bus", },
+	{ .compatible = "simple-bus",	.data = ONLY_BUS },
+	{ .compatible = "simple-mfd",	.data = ONLY_BUS },
+	{ .compatible = "isa",		.data = ONLY_BUS },
+	{ .compatible = "arm,amba-bus",	.data = ONLY_BUS },
 	{ /* sentinel */ }
 };
 MODULE_DEVICE_TABLE(of, simple_pm_bus_of_match);