driver core: platform: Emit a warning if a remove callback returned non-zero

The driver core ignores the return value of a bus' remove callback. However
a driver returning an error code is a hint that there is a problem,
probably a driver author who expects that returning e.g. -EBUSY has any
effect.

The right thing to do would be to make struct platform_driver::remove()
return void. With the immense number of platform drivers this is however a
big quest and I hope to prevent at least a few new drivers that return an
error code here.
Signed-off-by: Uwe Kleine-König <uwe@kleine-koenig.org>
Link: https://lore.kernel.org/r/20210207211537.19992-1-uwe@kleine-koenig.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/base/platform.c

@@ -1463,13 +1463,16 @@ static int platform_remove(struct device *_dev)
 {
 	struct platform_driver *drv = to_platform_driver(_dev->driver);
 	struct platform_device *dev = to_platform_device(_dev);
-	int ret = 0;
 
-	if (drv->remove)
-		ret = drv->remove(dev);
+	if (drv->remove) {
+		int ret = drv->remove(dev);
+
+		if (ret)
+			dev_warn(_dev, "remove callback returned a non-zero value. This will be ignored.\n");
+	}
 	dev_pm_domain_detach(_dev, true);
 
-	return ret;
+	return 0;
 }
 
 static void platform_shutdown(struct device *_dev)