driver core: prevent deferred probe with platform_driver_probe

Prevent drivers relying on platform_driver_probe from requesting
deferred probing in order to avoid further futile probe attempts (either
the driver has been unregistered or its probe function has been set to
platform_drv_probe_fail when probing is retried).

Note that several platform drivers currently return subsystem errors
from probe and that these can include -EPROBE_DEFER (e.g. if a gpio
request fails).

Add a warning to platform_drv_probe that can be used to catch drivers
that inadvertently request probe deferral while using
platform_driver_probe.

Signed-off-by: Johan Hovold <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/base/platform.c

···
 	if (ret && ACPI_HANDLE(_dev))
 		acpi_dev_pm_detach(_dev, true);
 
+	if (drv->prevent_deferred_probe && ret == -EPROBE_DEFER) {
+		dev_warn(_dev, "probe deferral not supported\n");
+		ret = -ENXIO;
+	}
+
 	return ret;
 }
 
···
 /**
  * platform_driver_probe - register driver for non-hotpluggable device
  * @drv: platform driver structure
- * @probe: the driver probe routine, probably from an __init section,
- *         must not return -EPROBE_DEFER.
+ * @probe: the driver probe routine, probably from an __init section
  *
  * Use this instead of platform_driver_register() when you know the device
  * is not hotpluggable and has already been registered, and you want to
···
  * into system-on-chip processors, where the controller devices have been
  * configured as part of board setup.
  *
- * This is incompatible with deferred probing so probe() must not
- * return -EPROBE_DEFER.
+ * Note that this is incompatible with deferred probing.
  *
  * Returns zero if the driver registered and bound to a device, else returns
  * a negative error code and with the driver not registered.
···
 		int (*probe)(struct platform_device *))
 {
 	int retval, code;
+
+	/*
+	 * Prevent driver from requesting probe deferral to avoid further
+	 * futile probe attempts.
+	 */
+	drv->prevent_deferred_probe = true;
 
 	/* make sure driver won't have bind/unbind attributes */
 	drv->driver.suppress_bind_attrs = true;

include/linux/platform_device.h

···
 	int (*resume)(struct platform_device *);
 	struct device_driver driver;
 	const struct platform_device_id *id_table;
+	bool prevent_deferred_probe;
 };
 
 #define to_platform_driver(drv)	(container_of((drv), struct platform_driver, \