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drivers/entropy: stm32 add seed error recovery

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This commit introduces an automatic recovery procedure in cases an
entropy source error was detected.
- On Series with soft reset support a soft rest is executed.
- On Series w/o soft reset support the pipeline is cleared by reading
  the RNG_DR 12 times.

With this changes the check for seed errors uses SEIS flag instead
of the SECS flag.

Signed-off-by: Thomas Stranger <thomas.stranger@outlook.com>
This commit is contained in:
Thomas Stranger 2021-07-15 16:59:29 +02:00 • committed by Christopher Friedt
commit 95c3916c60
1 changed files with 62 additions and 9 deletions
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71
drivers/entropy/entropy_stm32.c
View file

@ -30,6 +30,10 @@
#define IRQN DT_INST_IRQN(0)
#define IRQ_PRIO DT_INST_IRQ(0, priority)
#if defined(RNG_CR_CONDRST)
#define STM32_CONDRST_SUPPORT
#endif
/*
* This driver need to take into account all STM32 family:
* - simple rng without harware fifo and no DMA.
@ -107,30 +111,79 @@ static int entropy_stm32_got_error(RNG_TypeDef *rng)
return 1;
}
if (LL_RNG_IsActiveFlag_SECS(rng)) {
if (LL_RNG_IsActiveFlag_SEIS(rng)) {
return 1;
}
return 0;
}
#if defined(STM32_CONDRST_SUPPORT)
/* SOCS w/ soft-reset support: execute the reset */
static int recover_seed_error(RNG_TypeDef *rng)
{
uint32_t count_timeout = 0;
LL_RNG_EnableCondReset(rng);
LL_RNG_DisableCondReset(rng);
/* When reset process is done cond reset bit is read 0
* This typically takes: 2 AHB clock cycles + 2 RNG clock cycles.
*/
while (LL_RNG_IsEnabledCondReset(rng) ||
LL_RNG_IsActiveFlag_SEIS(rng) ||
LL_RNG_IsActiveFlag_SECS(rng)) {
count_timeout++;
if (count_timeout == 10) {
return -ETIMEDOUT;
}
}
return 0;
}
#else /* !STM32_CONDRST_SUPPORT */
/* SOCS w/o soft-reset support: flush pipeline */
static int recover_seed_error(RNG_TypeDef *rng)
{
LL_RNG_ClearFlag_SEIS(rng);
for (int i = 0; i < 12; ++i) {
LL_RNG_ReadRandData32(rng);
}
if (LL_RNG_IsActiveFlag_SEIS(rng) != 0) {
return -EIO;
}
return 0;
}
#endif /* !STM32_CONDRST_SUPPORT */
static int random_byte_get(void)
{
int retval = -EAGAIN;
unsigned int key;
RNG_TypeDef *rng = entropy_stm32_rng_data.rng;
key = irq_lock();
if ((LL_RNG_IsActiveFlag_DRDY(entropy_stm32_rng_data.rng) == 1)) {
if (entropy_stm32_got_error(entropy_stm32_rng_data.rng)) {
retval = -EIO;
} else {
retval = LL_RNG_ReadRandData32(
entropy_stm32_rng_data.rng);
retval &= 0xFF;
}
if (LL_RNG_IsActiveFlag_SEIS(rng) && (recover_seed_error(rng) < 0)) {
retval = -EIO;
goto out;
}
if ((LL_RNG_IsActiveFlag_DRDY(rng) == 1)) {
if (entropy_stm32_got_error(rng)) {
retval = -EIO;
goto out;
}
retval = LL_RNG_ReadRandData32(rng);
retval &= 0xFF;
}
out:
irq_unlock(key);
return retval;