ath9k: fix rng high cpu load

If no valid ADC randomness output, ath9k rng will continuously
reading ADC, which will cause high CPU load. So increase the
delay to wait for ADC ready.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=114261
Signed-off-by: Miaoqing Pan <miaoqing@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>

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

@@ -55,11 +55,26 @@ static int ath9k_rng_data_read(struct ath_softc *sc, u32 *buf, u32 buf_size)
 	return j << 2;
 }
 
+static u32 ath9k_rng_delay_get(u32 fail_stats)
+{
+	u32 delay;
+
+	if (fail_stats < 100)
+		delay = 10;
+	else if (fail_stats < 105)
+		delay = 1000;
+	else
+		delay = 10000;
+
+	return delay;
+}
+
 static int ath9k_rng_kthread(void *data)
 {
 	int bytes_read;
 	struct ath_softc *sc = data;
 	u32 *rng_buf;
+	u32 delay, fail_stats = 0;
 
 	rng_buf = kmalloc_array(ATH9K_RNG_BUF_SIZE, sizeof(u32), GFP_KERNEL);
 	if (!rng_buf)
@@ -69,10 +84,13 @@ static int ath9k_rng_kthread(void *data)
 		bytes_read = ath9k_rng_data_read(sc, rng_buf,
 						 ATH9K_RNG_BUF_SIZE);
 		if (unlikely(!bytes_read)) {
-			msleep_interruptible(10);
+			delay = ath9k_rng_delay_get(++fail_stats);
+			msleep_interruptible(delay);
 			continue;
 		}
 
+		fail_stats = 0;
+
 		/* sleep until entropy bits under write_wakeup_threshold */
 		add_hwgenerator_randomness((void *)rng_buf, bytes_read,
 					   ATH9K_RNG_ENTROPY(bytes_read));