drivers: entropy: gecko_trng: Fix blocking behavior

entropy_get_entropy() is allowed to block while waiting for
entropy. Don't exit with an error if entropy is exhausted,
wait instead. Move clock enable out of the inner loop to avoid
unnecessarily calling it multiple times.

Upstream-status: available
Signed-off-by: Aksel Skauge Mellbye <[email protected]>
(cherry picked from commit ad867a1)

Author: asmellby

drivers/entropy/entropy_gecko_trng.c

@@ -76,17 +76,16 @@ static int entropy_gecko_trng_get_entropy(const struct device *dev,
 
 	ARG_UNUSED(dev);
 
+#ifdef CONFIG_CRYPTO_ACC_GECKO_TRNG
+	CMU_ClockEnable(cmuClock_CRYPTOACC, true);
+#endif
+
 	while (length) {
 #ifndef CONFIG_CRYPTO_ACC_GECKO_TRNG
 		available = TRNG0->FIFOLEVEL * 4;
 #else
-		CMU_ClockEnable(cmuClock_CRYPTOACC, true);
 		available = S2_FIFO_LEVEL * 4;
 #endif
-		if (available == 0) {
-			return -EINVAL;
-		}
-
 		count = SL_MIN(length, available);
 		entropy_gecko_trng_read(buffer, count);
 		buffer += count;