hwrng: add devm_* interfaces

This change adds devm_hwrng_register and devm_hwrng_unregister which
use can simplify error unwinding and unbinding code paths in device
drivers.

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/char/hw_random/core.c

@@ -536,6 +536,48 @@ void hwrng_unregister(struct hwrng *rng)
 }
 EXPORT_SYMBOL_GPL(hwrng_unregister);
 
+static void devm_hwrng_release(struct device *dev, void *res)
+{
+	hwrng_unregister(*(struct hwrng **)res);
+}
+
+static int devm_hwrng_match(struct device *dev, void *res, void *data)
+{
+	struct hwrng **r = res;
+
+	if (WARN_ON(!r || !*r))
+		return 0;
+
+	return *r == data;
+}
+
+int devm_hwrng_register(struct device *dev, struct hwrng *rng)
+{
+	struct hwrng **ptr;
+	int error;
+
+	ptr = devres_alloc(devm_hwrng_release, sizeof(*ptr), GFP_KERNEL);
+	if (!ptr)
+		return -ENOMEM;
+
+	error = hwrng_register(rng);
+	if (error) {
+		devres_free(ptr);
+		return error;
+	}
+
+	*ptr = rng;
+	devres_add(dev, ptr);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(devm_hwrng_register);
+
+void devm_hwrng_unregister(struct device *dev, struct hwrng *rng)
+{
+	devres_release(dev, devm_hwrng_release, devm_hwrng_match, rng);
+}
+EXPORT_SYMBOL_GPL(devm_hwrng_unregister);
+
 static int __init hwrng_modinit(void)
 {
 	return register_miscdev();

include/linux/hw_random.h

@@ -50,10 +50,14 @@ struct hwrng {
 	struct completion cleanup_done;
 };
 
+struct device;
+
 /** Register a new Hardware Random Number Generator driver. */
 extern int hwrng_register(struct hwrng *rng);
+extern int devm_hwrng_register(struct device *dev, struct hwrng *rng);
 /** Unregister a Hardware Random Number Generator driver. */
 extern void hwrng_unregister(struct hwrng *rng);
+extern void devm_hwrng_unregister(struct device *dve, struct hwrng *rng);
 /** Feed random bits into the pool. */
 extern void add_hwgenerator_randomness(const char *buffer, size_t count, size_t entropy);