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hwrng: stm32 - rework error handling in stm32_rng_read()

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Try to conceal seed errors when possible. If, despite the error
concealing tries, a seed error is still present, then return an error.

A clock error does not compromise the hardware block and data can
still be read from RNG_DR. Just warn that the RNG clock is too slow
and clear RNG_SR.

Signed-off-by: Gatien Chevallier <gatien.chevallier@foss.st.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
This commit is contained in:
Gatien Chevallier 2023-09-21 10:02:57 +02:00 committed by Herbert Xu
parent 8f1c5227ec
commit b17bc6eb7c
1 changed files with 45 additions and 16 deletions
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61
drivers/char/hw_random/stm32-rng.c
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@ -43,6 +43,8 @@
#define RNG_HTCR 0x10
#define RNG_NB_RECOVER_TRIES 3
struct stm32_rng_data {
u32 cr;
u32 nscr;
@ -162,10 +164,10 @@ static int stm32_rng_conceal_seed_error(struct hwrng *rng)
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);
struct stm32_rng_private *priv = container_of(rng, struct stm32_rng_private, rng);
unsigned int i = 0;
int retval = 0, err = 0;
u32 sr;
int retval = 0;
pm_runtime_get_sync((struct device *) priv->rng.priv);
@ -174,30 +176,57 @@ 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);
/* Manage timeout which is based on timer and take */
/* care of initial delay time when enabling rng */
/*
* Manage timeout which is based on timer and take
* care of initial delay time when enabling the RNG.
*/
if (!sr && wait) {
int err;
err = readl_relaxed_poll_timeout_atomic(priv->base
+ RNG_SR,
sr, sr,
10, 50000);
if (err)
if (err) {
dev_err((struct device *)priv->rng.priv,
"%s: timeout %x!\n", __func__, sr);
}
/* If error detected or data not ready... */
if (sr != RNG_SR_DRDY) {
if (WARN_ONCE(sr & (RNG_SR_SEIS | RNG_SR_CEIS),
"bad RNG status - %x\n", sr))
writel_relaxed(0, priv->base + RNG_SR);
break;
}
} else if (!sr) {
/* The FIFO is being filled up */
break;
}
*(u32 *)data = readl_relaxed(priv->base + RNG_DR);
if (sr != RNG_SR_DRDY) {
if (sr & RNG_SR_SEIS) {
err = stm32_rng_conceal_seed_error(rng);
i++;
if (err && i > RNG_NB_RECOVER_TRIES) {
dev_err((struct device *)priv->rng.priv,
"Couldn't recover from seed error\n");
return -ENOTRECOVERABLE;
}
continue;
}
if (WARN_ONCE((sr & RNG_SR_CEIS), "RNG clock too slow - %x\n", sr))
writel_relaxed(0, priv->base + RNG_SR);
}
/* Late seed error case: DR being 0 is an error status */
*(u32 *)data = readl_relaxed(priv->base + RNG_DR);
if (!*(u32 *)data) {
err = stm32_rng_conceal_seed_error(rng);
i++;
if (err && i > RNG_NB_RECOVER_TRIES) {
dev_err((struct device *)priv->rng.priv,
"Couldn't recover from seed error");
return -ENOTRECOVERABLE;
}
continue;
}
i = 0;
retval += sizeof(u32);
data += sizeof(u32);
max -= sizeof(u32);