hwrng: bcm2835 - fix oops when rng h/w is accessed during registration

Commit "d9e7972 hwrng: add randomness to system from rng sources"
exposed a bug in the bcm2835-rng driver resulting in boot failure
on Raspberry Pi due to the following oops:

[   28.261523] BUG: soft lockup - CPU#0 stuck for 23s! [swapper:1]
[   28.271058]
[   28.275958] CPU: 0 PID: 1 Comm: swapper Not tainted 3.14.0+ #11
[   28.285374] task: db480000 ti: db484000 task.ti: db484000
[   28.294279] PC is at bcm2835_rng_read+0x28/0x48
[   28.302276] LR is at hwrng_register+0x1a8/0x238
.
.
.

The RNG h/w is not completely initialized and enabled before
hwrng_register() is called and so the bcm2835_rng_read() fails.
Fix this by making the warmup/enable writes before registering
the RNG source with the hwrng core.

Signed-off-by: Matt Porter <mporter@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 5 insertions, 5 deletions

diff --git a/drivers/char/hw_random/bcm2835-rng.c b/drivers/char/hw_random/bcm2835-rng.c
index 8c3b255e629a..e900961cdd2e 100644
--- a/drivers/char/hw_random/bcm2835-rng.c
+++ b/drivers/char/hw_random/bcm2835-rng.c
@@ -61,18 +61,18 @@ static int bcm2835_rng_probe(struct platform_device *pdev)
         }
         bcm2835_rng_ops.priv = (unsigned long)rng_base;
 
+        /* set warm-up count & enable */
+        __raw_writel(RNG_WARMUP_COUNT, rng_base + RNG_STATUS);
+        __raw_writel(RNG_RBGEN, rng_base + RNG_CTRL);
+
         /* register driver */
         err = hwrng_register(&bcm2835_rng_ops);
         if (err) {
                 dev_err(dev, "hwrng registration failed\n");
                 iounmap(rng_base);
-        } else {
+        } else
                 dev_info(dev, "hwrng registered\n");
 
-                /* set warm-up count & enable */
-                __raw_writel(RNG_WARMUP_COUNT, rng_base + RNG_STATUS);
-                __raw_writel(RNG_RBGEN, rng_base + RNG_CTRL);
-        }
         return err;
 }