[PATCH v2 1/2] hwrng: stm32 - use pm_runtime_resume_and_get()

[Marek Vasut]

include/linux/pm_runtime.h pm_runtime_get_sync() description suggests to
... consider using pm_runtime_resume_and_get() instead of it, especially
if its return value is checked by the caller, as this is likely to result
in cleaner code.

This is indeed better, switch to pm_runtime_resume_and_get() which
correctly suspends the device again in case of failure. Also add error
checking into the RNG driver in case pm_runtime_resume_and_get() does
fail, which is currently not done, and it does detect sporadic -EACCES
error return after resume, which would otherwise lead to a hang due to
register access on un-resumed hardware. Now the read simply errors out
and the system does not hang.

Acked-by: Gatien Chevallier <gatien.chevallier at foss.st.com>
Signed-off-by: Marek Vasut <marex at denx.de>
---
Cc: "Uwe Kleine-König" <u.kleine-koenig at pengutronix.de>
Cc: Alexandre Torgue <alexandre.torgue at foss.st.com>
Cc: Gatien Chevallier <gatien.chevallier at foss.st.com>
Cc: Herbert Xu <herbert at gondor.apana.org.au>
Cc: Marek Vasut <marex at denx.de>
Cc: Maxime Coquelin <mcoquelin.stm32 at gmail.com>
Cc: Olivia Mackall <olivia at selenic.com>
Cc: Rob Herring <robh at kernel.org>
Cc: Yang Yingliang <yangyingliang at huawei.com>
Cc: kernel at dh-electronics.com
Cc: linux-arm-kernel at lists.infradead.org
Cc: linux-crypto at vger.kernel.org
Cc: linux-stm32 at st-md-mailman.stormreply.com
---
V2: Add AB from Gatien
---
 drivers/char/hw_random/stm32-rng.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/char/hw_random/stm32-rng.c b/drivers/char/hw_random/stm32-rng.c
index 0e903d6e22e30..6dec4adc49853 100644
--- a/drivers/char/hw_random/stm32-rng.c
+++ b/drivers/char/hw_random/stm32-rng.c
@@ -187,7 +187,9 @@ static int stm32_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
 	int retval = 0, err = 0;
 	u32 sr;
 
-	pm_runtime_get_sync((struct device *) priv->rng.priv);
+	retval = pm_runtime_resume_and_get((struct device *)priv->rng.priv);
+	if (retval)
+		return retval;
 
 	if (readl_relaxed(priv->base + RNG_SR) & RNG_SR_SEIS)
 		stm32_rng_conceal_seed_error(rng);
-- 
2.43.0