linux-kernel - [PATCH] hwrng: omap - Fix RNG wait loop timeout

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Message-Id: <1571054565-6991-1-git-send-email-sumit.garg@linaro.org>
Date:   Mon, 14 Oct 2019 17:32:45 +0530
From:   Sumit Garg <sumit.garg@...aro.org>
To:     linux-crypto@...r.kernel.org
Cc:     dsaxena@...xity.net, herbert@...dor.apana.org.au, mpm@...enic.com,
        romain.perier@...e-electrons.com, arnd@...db.de,
        gregkh@...uxfoundation.org, daniel.thompson@...aro.org,
        ralph.siemsen@...aro.org, milan.stevanovic@...com,
        ryan.harkin@...aro.org, linux-kernel@...r.kernel.org,
        Sumit Garg <sumit.garg@...aro.org>, stable@...r.kernel.org
Subject: [PATCH] hwrng: omap - Fix RNG wait loop timeout

Existing RNG data read timeout is 200us but it doesn't cover EIP76 RNG
data rate which takes approx. 700us to produce 16 bytes of output data
as per testing results. So configure the timeout as 1000us to also take
account of lack of udelay()'s reliability.

Fixes: 383212425c92 ("hwrng: omap - Add device variant for SafeXcel IP-76 found in Armada 8K")
Cc: <stable@...r.kernel.org>
Signed-off-by: Sumit Garg <sumit.garg@...aro.org>
---
 drivers/char/hw_random/omap-rng.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/char/hw_random/omap-rng.c b/drivers/char/hw_random/omap-rng.c
index b27f396..e329f82 100644
--- a/drivers/char/hw_random/omap-rng.c
+++ b/drivers/char/hw_random/omap-rng.c
@@ -66,6 +66,13 @@
 #define OMAP4_RNG_OUTPUT_SIZE			0x8
 #define EIP76_RNG_OUTPUT_SIZE			0x10
 
+/*
+ * EIP76 RNG takes approx. 700us to produce 16 bytes of output data
+ * as per testing results. And to account for the lack of udelay()'s
+ * reliability, we keep the timeout as 1000us.
+ */
+#define RNG_DATA_FILL_TIMEOUT			100
+
 enum {
 	RNG_OUTPUT_0_REG = 0,
 	RNG_OUTPUT_1_REG,
@@ -176,7 +183,7 @@ static int omap_rng_do_read(struct hwrng *rng, void *data, size_t max,
 	if (max < priv->pdata->data_size)
 		return 0;
 
-	for (i = 0; i < 20; i++) {
+	for (i = 0; i < RNG_DATA_FILL_TIMEOUT; i++) {
 		present = priv->pdata->data_present(priv);
 		if (present || !wait)
 			break;
-- 
2.7.4