2 files changed, 23 insertions, 0 deletions

diff --git a/drivers/char/random.c b/drivers/char/random.c
index d3bb7927fb49..914b1575df8f 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -250,6 +250,7 @@
 #include <linux/interrupt.h>
 #include <linux/mm.h>
 #include <linux/spinlock.h>
+#include <linux/kthread.h>
 #include <linux/percpu.h>
 #include <linux/cryptohash.h>
 #include <linux/fips.h>
@@ -1750,3 +1751,23 @@ randomize_range(unsigned long start, unsigned long end, unsigned long len)
                 return 0;
         return PAGE_ALIGN(get_random_int() % range + start);
 }
+
+/* Interface for in-kernel drivers of true hardware RNGs.
+ * Those devices may produce endless random bits and will be throttled
+ * when our pool is full.
+ */
+void add_hwgenerator_randomness(const char *buffer, size_t count,
+                                size_t entropy)
+{
+        struct entropy_store *poolp = &input_pool;
+
+        /* Suspend writing if we're above the trickle threshold.
+         * We'll be woken up again once below random_write_wakeup_thresh,
+         * or when the calling thread is about to terminate.
+         */
+        wait_event_interruptible(random_write_wait, kthread_should_stop() ||
+                        ENTROPY_BITS(&input_pool) <= random_write_wakeup_bits);
+        mix_pool_bytes(poolp, buffer, count);
+        credit_entropy_bits(poolp, entropy);
+}
+EXPORT_SYMBOL_GPL(add_hwgenerator_randomness);
diff --git a/include/linux/hw_random.h b/include/linux/hw_random.h
index b4b0eef5fddf..3f075ff00411 100644
--- a/include/linux/hw_random.h
+++ b/include/linux/hw_random.h
@@ -47,5 +47,7 @@ struct hwrng {
 extern int hwrng_register(struct hwrng *rng);
 /** Unregister a Hardware Random Number Generator driver. */
 extern void hwrng_unregister(struct hwrng *rng);
+/** Feed random bits into the pool. */
+extern void add_hwgenerator_randomness(const char *buffer, size_t count, size_t entropy);
 
 #endif /* LINUX_HWRANDOM_H_ */