diff options
Diffstat (limited to 'drivers/rng/stm32_rng.c')
| -rw-r--r-- | drivers/rng/stm32_rng.c | 163 |
1 files changed, 140 insertions, 23 deletions
diff --git a/drivers/rng/stm32_rng.c b/drivers/rng/stm32_rng.c index f943acd7d22..b1a790b217f 100644 --- a/drivers/rng/stm32_rng.c +++ b/drivers/rng/stm32_rng.c @@ -32,6 +32,8 @@ #define RNG_DR 0x08 +#define RNG_NB_RECOVER_TRIES 3 + /* * struct stm32_rng_data - RNG compat data * @@ -52,45 +54,160 @@ struct stm32_rng_plat { 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_plat *pdata) +{ + u32 sr = readl_relaxed(pdata->base + RNG_SR); + u32 cr = readl_relaxed(pdata->base + RNG_CR); + int err; + + if (sr & RNG_SR_SECS) { + /* Conceal by resetting the subsystem (step 1.) */ + writel_relaxed(cr | RNG_CR_CONDRST, pdata->base + RNG_CR); + writel_relaxed(cr & ~RNG_CR_CONDRST, pdata->base + RNG_CR); + } else { + /* RNG auto-reset (step 2.) */ + writel_relaxed(sr & ~RNG_SR_SEIS, pdata->base + RNG_SR); + return 0; + } + + err = readl_relaxed_poll_timeout(pdata->base + RNG_SR, sr, !(sr & RNG_CR_CONDRST), 100000); + if (err) { + log_err("%s: timeout %x\n", __func__, sr); + return err; + } + + /* Check SEIS is cleared (step 2.) */ + if (readl_relaxed(pdata->base + RNG_SR) & RNG_SR_SEIS) + return -EINVAL; + + err = readl_relaxed_poll_timeout(pdata->base + RNG_SR, sr, !(sr & RNG_SR_SECS), 100000); + if (err) { + log_err("%s: timeout %x\n", __func__, sr); + return err; + } + + 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_plat *pdata) +{ + uint i = 0; + u32 sr = readl_relaxed(pdata->base + RNG_SR); + + writel_relaxed(sr & ~RNG_SR_SEIS, pdata->base + RNG_SR); + + for (i = 12; i != 0; i--) + (void)readl_relaxed(pdata->base + RNG_DR); + + if (readl_relaxed(pdata->base + RNG_SR) & RNG_SR_SEIS) + return -EINVAL; + + return 0; +} + +static int stm32_rng_conceal_seed_error(struct stm32_rng_plat *pdata) +{ + log_debug("Concealing RNG seed error\n"); + + if (pdata->data->has_cond_reset) + return stm32_rng_conceal_seed_error_cond_reset(pdata); + else + return stm32_rng_conceal_seed_error_sw_reset(pdata); +}; + static int stm32_rng_read(struct udevice *dev, void *data, size_t len) { - int retval, i; - u32 sr, count, reg; + int retval; + u32 sr, reg; size_t increment; struct stm32_rng_plat *pdata = dev_get_plat(dev); + uint tries = 0; while (len > 0) { retval = readl_poll_timeout(pdata->base + RNG_SR, sr, - sr & RNG_SR_DRDY, 10000); - if (retval) + sr, 10000); + if (retval) { + log_err("%s: Timeout RNG no data", __func__); return retval; + } - if (sr & (RNG_SR_SEIS | RNG_SR_SECS)) { - /* As per SoC TRM */ - clrbits_le32(pdata->base + RNG_SR, RNG_SR_SEIS); - for (i = 0; i < 12; i++) - readl(pdata->base + RNG_DR); - if (readl(pdata->base + RNG_SR) & RNG_SR_SEIS) { - log_err("RNG Noise"); - return -EIO; + if (sr != RNG_SR_DRDY) { + if (sr & RNG_SR_SEIS) { + retval = stm32_rng_conceal_seed_error(pdata); + tries++; + if (retval || tries > RNG_NB_RECOVER_TRIES) { + log_err("%s: Couldn't recover from seed error", __func__); + return -ENOTRECOVERABLE; + } + + /* Start again */ + continue; + } + + if (sr & RNG_SR_CEIS) { + log_info("RNG clock too slow"); + writel_relaxed(0, pdata->base + RNG_SR); } - /* start again */ - continue; } /* * Once the DRDY bit is set, the RNG_DR register can - * be read four consecutive times. + * be read up to four consecutive times. */ - count = 4; - while (len && count) { - reg = readl(pdata->base + RNG_DR); - memcpy(data, ®, min(len, sizeof(u32))); - increment = min(len, sizeof(u32)); - data += increment; - len -= increment; - count--; + reg = readl(pdata->base + RNG_DR); + /* Late seed error case: DR being 0 is an error status */ + if (!reg) { + retval = stm32_rng_conceal_seed_error(pdata); + tries++; + + if (retval || tries > RNG_NB_RECOVER_TRIES) { + log_err("%s: Couldn't recover from seed error", __func__); + return -ENOTRECOVERABLE; + } + + /* Start again */ + continue; } + + increment = min(len, sizeof(u32)); + memcpy(data, ®, increment); + data += increment; + len -= increment; + + tries = 0; } return 0; |