ath9k: use hw_random API instead of directly dumping into random.c

Hardware random number generators are supposed to use the hw_random
framework. This commit turns ath9k's kthread-based design into a proper
hw_random driver.

Cc: Toke Høiland-Jørgensen <toke@redhat.com>
Cc: Kalle Valo <kvalo@kernel.org>
Cc: Rui Salvaterra <rsalvaterra@gmail.com>
Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Tested-by: Rui Salvaterra <rsalvaterra@gmail.com>
Acked-by: Toke Høiland-Jørgensen <toke@toke.dk>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20220216113323.53332-1-Jason@zx2c4.com

drivers/net/wireless/ath/ath9k/ath9k.h

@@ -1071,8 +1071,9 @@ struct ath_softc {
 #endif
 
 #ifdef CONFIG_ATH9K_HWRNG
+	struct hwrng rng_ops;
 	u32 rng_last;
-	struct task_struct *rng_task;
+	char rng_name[sizeof("ath9k_65535")];
 #endif
 };
 

drivers/net/wireless/ath/ath9k/rng.c

@@ -21,11 +21,6 @@
 #include "hw.h"
 #include "ar9003_phy.h"
 
-#define ATH9K_RNG_BUF_SIZE	320
-#define ATH9K_RNG_ENTROPY(x)	(((x) * 8 * 10) >> 5) /* quality: 10/32 */
-
-static DECLARE_WAIT_QUEUE_HEAD(rng_queue);
-
 static int ath9k_rng_data_read(struct ath_softc *sc, u32 *buf, u32 buf_size)
 {
 	int i, j;
@@ -71,61 +66,56 @@ static u32 ath9k_rng_delay_get(u32 fail_stats)
 	return delay;
 }
 
-static int ath9k_rng_kthread(void *data)
+static int ath9k_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
 {
-	int bytes_read;
-	struct ath_softc *sc = data;
-	u32 *rng_buf;
-	u32 delay, fail_stats = 0;
+	struct ath_softc *sc = container_of(rng, struct ath_softc, rng_ops);
+	u32 fail_stats = 0, word;
+	int bytes_read = 0;
 
-	rng_buf = kmalloc_array(ATH9K_RNG_BUF_SIZE, sizeof(u32), GFP_KERNEL);
-	if (!rng_buf)
-		goto out;
-
-	while (!kthread_should_stop()) {
-		bytes_read = ath9k_rng_data_read(sc, rng_buf,
-						 ATH9K_RNG_BUF_SIZE);
-		if (unlikely(!bytes_read)) {
-			delay = ath9k_rng_delay_get(++fail_stats);
-			wait_event_interruptible_timeout(rng_queue,
-							 kthread_should_stop(),
-							 msecs_to_jiffies(delay));
-			continue;
+	for (;;) {
+		if (max & ~3UL)
+			bytes_read = ath9k_rng_data_read(sc, buf, max >> 2);
+		if ((max & 3UL) && ath9k_rng_data_read(sc, &word, 1)) {
+			memcpy(buf + bytes_read, &word, max & 3UL);
+			bytes_read += max & 3UL;
+			memzero_explicit(&word, sizeof(word));
 		}
+		if (!wait || !max || likely(bytes_read) || fail_stats > 110)
+			break;
 
-		fail_stats = 0;
-
-		/* sleep until entropy bits under write_wakeup_threshold */
-		add_hwgenerator_randomness((void *)rng_buf, bytes_read,
-					   ATH9K_RNG_ENTROPY(bytes_read));
+		msleep_interruptible(ath9k_rng_delay_get(++fail_stats));
 	}
 
-	kfree(rng_buf);
-out:
-	sc->rng_task = NULL;
-
-	return 0;
+	if (wait && !bytes_read && max)
+		bytes_read = -EIO;
+	return bytes_read;
 }
 
 void ath9k_rng_start(struct ath_softc *sc)
 {
+	static atomic_t serial = ATOMIC_INIT(0);
 	struct ath_hw *ah = sc->sc_ah;
 
-	if (sc->rng_task)
+	if (sc->rng_ops.read)
 		return;
 
 	if (!AR_SREV_9300_20_OR_LATER(ah))
 		return;
 
-	sc->rng_task = kthread_run(ath9k_rng_kthread, sc, "ath9k-hwrng");
-	if (IS_ERR(sc->rng_task))
-		sc->rng_task = NULL;
+	snprintf(sc->rng_name, sizeof(sc->rng_name), "ath9k_%u",
+		 (atomic_inc_return(&serial) - 1) & U16_MAX);
+	sc->rng_ops.name = sc->rng_name;
+	sc->rng_ops.read = ath9k_rng_read;
+	sc->rng_ops.quality = 320;
+
+	if (devm_hwrng_register(sc->dev, &sc->rng_ops))
+		sc->rng_ops.read = NULL;
 }
 
 void ath9k_rng_stop(struct ath_softc *sc)
 {
-	if (sc->rng_task) {
-		kthread_stop(sc->rng_task);
-		sc->rng_task = NULL;
+	if (sc->rng_ops.read) {
+		devm_hwrng_unregister(sc->dev, &sc->rng_ops);
+		sc->rng_ops.read = NULL;
 	}
 }