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hwrng: stm32 - implement error concealment

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The RNG driver should be capable of recovering from an error. Implement
an error concealment API. This avoids irrecoverable RNG state.

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 10:02:56 +02:00 committed by Herbert Xu
parent 6b85a7e141
commit 8f1c5227ec
1 changed files with 110 additions and 4 deletions
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114
drivers/char/hw_random/stm32-rng.c
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@ -29,10 +29,12 @@
#define RNG_CR_ENTROPY_SRC_MASK (RNG_CR_CONFIG1 | RNG_CR_NISTC | RNG_CR_CONFIG2 | RNG_CR_CONFIG3)
#define RNG_CR_CONFIG_MASK (RNG_CR_ENTROPY_SRC_MASK | RNG_CR_CED)
#define RNG_SR 0x04
#define RNG_SR_SEIS BIT(6)
#define RNG_SR_CEIS BIT(5)
#define RNG_SR_DRDY BIT(0)
#define RNG_SR 0x04
#define RNG_SR_DRDY BIT(0)
#define RNG_SR_CECS BIT(1)
#define RNG_SR_SECS BIT(2)
#define RNG_SR_CEIS BIT(5)
#define RNG_SR_SEIS BIT(6)
#define RNG_DR 0x08
@ -57,6 +59,107 @@ struct stm32_rng_private {
bool ced;
};
/*
* Extracts from the STM32 RNG specification when RNG supports CONDRST.
*
* When a noise source (or seed) error occurs, the RNG stops generating
* random numbers and sets to “1” both SEIS and SECS bits to indicate
* that a seed error occurred. (...)
*
* 1. Software reset by writing CONDRST at 1 and at 0 (see bitfield
* description for details). This step is needed only if SECS is set.
* Indeed, when SEIS is set and SECS is cleared it means RNG performed
* the reset automatically (auto-reset).
* 2. If SECS was set in step 1 (no auto-reset) wait for CONDRST
* to be cleared in the RNG_CR register, then confirm that SEIS is
* cleared in the RNG_SR register. Otherwise just clear SEIS bit in
* the RNG_SR register.
* 3. If SECS was set in step 1 (no auto-reset) wait for SECS to be
* cleared by RNG. The random number generation is now back to normal.
*/
static int stm32_rng_conceal_seed_error_cond_reset(struct stm32_rng_private *priv)
{
struct device *dev = (struct device *)priv->rng.priv;
u32 sr = readl_relaxed(priv->base + RNG_SR);
u32 cr = readl_relaxed(priv->base + RNG_CR);
int err;
if (sr & RNG_SR_SECS) {
/* Conceal by resetting the subsystem (step 1.) */
writel_relaxed(cr | RNG_CR_CONDRST, priv->base + RNG_CR);
writel_relaxed(cr & ~RNG_CR_CONDRST, priv->base + RNG_CR);
} else {
/* RNG auto-reset (step 2.) */
writel_relaxed(sr & ~RNG_SR_SEIS, priv->base + RNG_SR);
goto end;
}
err = readl_relaxed_poll_timeout_atomic(priv->base + RNG_CR, cr, !(cr & RNG_CR_CONDRST), 10,
100000);
if (err) {
dev_err(dev, "%s: timeout %x\n", __func__, sr);
return err;
}
/* Check SEIS is cleared (step 2.) */
if (readl_relaxed(priv->base + RNG_SR) & RNG_SR_SEIS)
return -EINVAL;
err = readl_relaxed_poll_timeout_atomic(priv->base + RNG_SR, sr, !(sr & RNG_SR_SECS), 10,
100000);
if (err) {
dev_err(dev, "%s: timeout %x\n", __func__, sr);
return err;
}
end:
return 0;
}
/*
* Extracts from the STM32 RNG specification, when CONDRST is not supported
*
* When a noise source (or seed) error occurs, the RNG stops generating
* random numbers and sets to “1” both SEIS and SECS bits to indicate
* that a seed error occurred. (...)
*
* The following sequence shall be used to fully recover from a seed
* error after the RNG initialization:
* 1. Clear the SEIS bit by writing it to “0”.
* 2. Read out 12 words from the RNG_DR register, and discard each of
* them in order to clean the pipeline.
* 3. Confirm that SEIS is still cleared. Random number generation is
* back to normal.
*/
static int stm32_rng_conceal_seed_error_sw_reset(struct stm32_rng_private *priv)
{
unsigned int i = 0;
u32 sr = readl_relaxed(priv->base + RNG_SR);
writel_relaxed(sr & ~RNG_SR_SEIS, priv->base + RNG_SR);
for (i = 12; i != 0; i--)
(void)readl_relaxed(priv->base + RNG_DR);
if (readl_relaxed(priv->base + RNG_SR) & RNG_SR_SEIS)
return -EINVAL;
return 0;
}
static int stm32_rng_conceal_seed_error(struct hwrng *rng)
{
struct stm32_rng_private *priv = container_of(rng, struct stm32_rng_private, rng);
dev_dbg((struct device *)priv->rng.priv, "Concealing seed error\n");
if (priv->data->has_cond_reset)
return stm32_rng_conceal_seed_error_cond_reset(priv);
else
return stm32_rng_conceal_seed_error_sw_reset(priv);
};
static int stm32_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
{
struct stm32_rng_private *priv =
@ -66,6 +169,9 @@ static int stm32_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
pm_runtime_get_sync((struct device *) priv->rng.priv);
if (readl_relaxed(priv->base + RNG_SR) & RNG_SR_SEIS)
stm32_rng_conceal_seed_error(rng);
while (max >= sizeof(u32)) {
sr = readl_relaxed(priv->base + RNG_SR);
/* Manage timeout which is based on timer and take */