linux-kernel - [PATCH] hwrng: bcm2835: add reset support

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Message-Id: <20210222194510.14004-1-noltari@gmail.com>
Date:   Mon, 22 Feb 2021 20:45:10 +0100
From:   Álvaro Fernández Rojas 
        <noltari@...il.com>
To:     Matt Mackall <mpm@...enic.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        Florian Fainelli <f.fainelli@...il.com>,
        Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>,
        bcm-kernel-feedback-list@...adcom.com,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Rikard Falkeborn <rikard.falkeborn@...il.com>,
        Álvaro Fernández Rojas 
        <noltari@...il.com>, linux-crypto@...r.kernel.org,
        linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH] hwrng: bcm2835: add reset support

BCM6368 devices need to reset the in order to generate true random numbers.
This is what BCM6368 produces without a reset:
root@...nWrt:/# cat /dev/hwrng | rngtest -c 1000
rngtest 6.10
Copyright (c) 2004 by Henrique de Moraes Holschuh
This is free software; see the source for copying conditions.  There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

rngtest: starting FIPS tests...
rngtest: bits received from input: 20000032
rngtest: FIPS 140-2 successes: 0
rngtest: FIPS 140-2 failures: 1000
rngtest: FIPS 140-2(2001-10-10) Monobit: 2
rngtest: FIPS 140-2(2001-10-10) Poker: 1000
rngtest: FIPS 140-2(2001-10-10) Runs: 1000
rngtest: FIPS 140-2(2001-10-10) Long run: 30
rngtest: FIPS 140-2(2001-10-10) Continuous run: 0
rngtest: input channel speed: (min=37.253; avg=320.827; max=635.783)Mibits/s
rngtest: FIPS tests speed: (min=12.141; avg=15.034; max=16.428)Mibits/s
rngtest: Program run time: 1336176 microseconds
cat: write error: Broken pipe

Signed-off-by: Álvaro Fernández Rojas <noltari@...il.com>
---
 drivers/char/hw_random/bcm2835-rng.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/char/hw_random/bcm2835-rng.c b/drivers/char/hw_random/bcm2835-rng.c
index 1a7c43b43c6b..1b93a896d8e8 100644
--- a/drivers/char/hw_random/bcm2835-rng.c
+++ b/drivers/char/hw_random/bcm2835-rng.c
@@ -13,6 +13,7 @@
 #include <linux/platform_device.h>
 #include <linux/printk.h>
 #include <linux/clk.h>
+#include <linux/reset.h>

 #define RNG_CTRL	0x0
 #define RNG_STATUS	0x4
@@ -32,6 +33,7 @@ struct bcm2835_rng_priv {
 	void __iomem *base;
 	bool mask_interrupts;
 	struct clk *clk;
+	struct reset_control *reset;
 };

 static inline struct bcm2835_rng_priv *to_rng_priv(struct hwrng *rng)
@@ -94,6 +96,10 @@ static int bcm2835_rng_init(struct hwrng *rng)
 			return ret;
 	}

+	ret = reset_control_reset(priv->reset);
+	if (ret)
+		return ret;
+
 	if (priv->mask_interrupts) {
 		/* mask the interrupt */
 		val = rng_readl(priv, RNG_INT_MASK);
@@ -159,6 +165,10 @@ static int bcm2835_rng_probe(struct platform_device *pdev)
 	if (PTR_ERR(priv->clk) == -EPROBE_DEFER)
 		return -EPROBE_DEFER;

+	priv->reset = devm_reset_control_get_optional_exclusive(dev, NULL);
+	if (IS_ERR(priv->reset))
+		return PTR_ERR(priv->reset);
+
 	priv->rng.name = pdev->name;
 	priv->rng.init = bcm2835_rng_init;
 	priv->rng.read = bcm2835_rng_read;
-- 
2.20.1