platform: Add platform_find_device_by_driver() helper

Provide a helper to lookup platform devices by matching device
driver in order to avoid drivers trying to use platform bus
internals.

Cc: Eric Anholt <[e-mail]>
Cc: Greg Kroah-Hartman <[e-mail]>
Cc: "Heiko Stübner" <[e-mail]>
Cc: Inki Dae <[e-mail]>
Cc: "Rafael J. Wysocki" <[e-mail]>
Cc: Sandy Huang <[e-mail]>
Cc: Seung-Woo Kim <[e-mail]>
Tested-by: Heiko Stuebner <[e-mail]>
Signed-off-by: Suzuki K Poulose <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/base/platform.c

···
 };
 EXPORT_SYMBOL_GPL(platform_bus_type);
 
+/**
+ * platform_find_device_by_driver - Find a platform device with a given
+ * driver.
+ * @start: The device to start the search from.
+ * @drv: The device driver to look for.
+ */
+struct device *platform_find_device_by_driver(struct device *start,
+					      const struct device_driver *drv)
+{
+	return bus_find_device(&platform_bus_type, start, drv,
+			       (void *)platform_match);
+}
+EXPORT_SYMBOL_GPL(platform_find_device_by_driver);
+
 int __init platform_bus_init(void)
 {
 	int error;

drivers/gpu/drm/exynos/exynos_drm_drv.c

···
 		if (!info->driver || !(info->flags & DRM_COMPONENT_DRIVER))
 			continue;
 
-		while ((d = bus_find_device(&platform_bus_type, p,
-					    &info->driver->driver,
-					    (void *)platform_bus_type.match))) {
+		while ((d = platform_find_device_by_driver(p, &info->driver->driver))) {
 			put_device(p);
 
 			if (!(info->flags & DRM_FIMC_DEVICE) ||
···
 		if (!info->driver || !(info->flags & DRM_VIRTUAL_DEVICE))
 			continue;
 
-		while ((dev = bus_find_device(&platform_bus_type, NULL,
-					    &info->driver->driver,
-					    (void *)platform_bus_type.match))) {
+		while ((dev = platform_find_device_by_driver(NULL,
+						&info->driver->driver))) {
 			put_device(dev);
 			platform_device_unregister(to_platform_device(dev));
 		}

drivers/gpu/drm/mcde/mcde_drv.c

···
 		struct device_driver *drv = &mcde_component_drivers[i]->driver;
 		struct device *p = NULL, *d;
 
-		while ((d = bus_find_device(&platform_bus_type, p, drv,
-					    (void *)platform_bus_type.match))) {
+		while ((d = platform_find_device_by_driver(p, drv))) {
 			put_device(p);
 			component_match_add(dev, &match, mcde_compare_dev, d);
 			p = d;

drivers/gpu/drm/rockchip/rockchip_drm_drv.c

···
 		struct device *p = NULL, *d;
 
 		do {
-			d = bus_find_device(&platform_bus_type, p, &drv->driver,
-					    (void *)platform_bus_type.match);
+			d = platform_find_device_by_driver(p, &drv->driver);
 			put_device(p);
 			p = d;
 

drivers/gpu/drm/vc4/vc4_drv.c

···
 		struct device_driver *drv = &drivers[i]->driver;
 		struct device *p = NULL, *d;
 
-		while ((d = bus_find_device(&platform_bus_type, p, drv,
-					    (void *)platform_bus_type.match))) {
+		while ((d = platform_find_device_by_driver(p, drv))) {
 			put_device(p);
 			component_match_add(dev, match, compare_dev, d);
 			p = d;

include/linux/platform_device.h

···
 extern void arch_setup_pdev_archdata(struct platform_device *);
 extern struct resource *platform_get_resource(struct platform_device *,
 					      unsigned int, unsigned int);
+extern struct device *
+platform_find_device_by_driver(struct device *start,
+			       const struct device_driver *drv);
 extern void __iomem *
 devm_platform_ioremap_resource(struct platform_device *pdev,
 			       unsigned int index);