Re: [PATCH] hwrng: stm32 - fix build warning

Arnd Bergmann
2016-05-24T08:33:19Z

On Tuesday, May 24, 2016 9:59:41 AM CEST Maxime Coquelin wrote:
> 2016-05-23 22:35 GMT+02:00 Arnd Bergmann <arnd@arndb.de>:
> > On Monday, May 23, 2016 6:14:08 PM CEST Sudip Mukherjee wrote:
> >> diff --git a/drivers/char/hw_random/stm32-rng.c b/drivers/char/hw_random/stm32-rng.c
> >> index 92a8106..0533370 100644
> >> --- a/drivers/char/hw_random/stm32-rng.c
> >> +++ b/drivers/char/hw_random/stm32-rng.c
> >> @@ -52,7 +52,7 @@ static int stm32_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
> >> {
> >> struct stm32_rng_private *priv =
> >> container_of(rng, struct stm32_rng_private, rng);
> >> - u32 sr;
> >> + u32 sr = 0;
> >> int retval = 0;
> >>
> >> pm_runtime_get_sync((struct device *) priv->rng.priv);
> >
> > Does this work as well?
> >
> > diff --git a/drivers/char/hw_random/stm32-rng.c b/drivers/char/hw_random/stm32-rng.c
> > index 92a810648bd0..5c836b0afa40 100644
> > --- a/drivers/char/hw_random/stm32-rng.c
> > +++ b/drivers/char/hw_random/stm32-rng.c
> > @@ -79,7 +79,7 @@ static int stm32_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
> > max -= sizeof(u32);
> > }
> >
> > - if (WARN_ONCE(sr & (RNG_SR_SEIS | RNG_SR_CEIS),
> > + if (WARN_ONCE(retval > 0 && (sr & (RNG_SR_SEIS | RNG_SR_CEIS)),
> > "bad RNG status - %x\n", sr))
> > writel_relaxed(0, priv->base + RNG_SR);
> >
> > I think it would be nicer to not add a bogus initialization.
> Hmm, no sure this nicer.
> The while loop can break before retval is incremented when sr value is
> not expected (sr != RNG_SR_DRDY).
> In that case, we certainly want to print sr value.

Ah, you are right.

> Maybe the better way is just to initialize sr with status register content?

> pm_runtime_get_sync((struct device *) priv->rng.priv);
>
>+ sr = readl_relaxed(priv->base + RNG_SR);
> while (max > sizeof(u32)) {
>- sr = readl_relaxed(priv->base + RNG_SR);
> if (!sr && wait) {
> unsigned int timeout = RNG_TIMEOUT;

I think that introduces a bug: you really want to read the status
register on each loop iteration.

How about moving the error handling into the loop itself?

Arnd

diff --git a/drivers/char/hw_random/stm32-rng.c b/drivers/char/hw_random/stm32-rng.c
index 92a810648bd0..fceacd809462 100644
--- a/drivers/char/hw_random/stm32-rng.c
+++ b/drivers/char/hw_random/stm32-rng.c
@@ -59,6 +59,10 @@ static int stm32_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)

while (max > sizeof(u32)) {
sr = readl_relaxed(priv->base + RNG_SR);
+ if (WARN_ONCE(sr & (RNG_SR_SEIS | RNG_SR_CEIS),
+ "bad RNG status - %x\n", sr))
+ writel_relaxed(0, priv->base + RNG_SR);
+
if (!sr && wait) {
unsigned int timeout = RNG_TIMEOUT;

@@ -79,10 +83,6 @@ static int stm32_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
max -= sizeof(u32);
}

- if (WARN_ONCE(sr & (RNG_SR_SEIS | RNG_SR_CEIS),
- "bad RNG status - %x\n", sr))
- writel_relaxed(0, priv->base + RNG_SR);
-
pm_runtime_mark_last_busy((struct device *) priv->rng.priv);
pm_runtime_put_sync_autosuspend((struct device *) priv->rng.priv);