From 8f1c5227eccb4e1c47b30bbe4a63b87535d12674 Mon Sep 17 00:00:00 2001 From: Gatien Chevallier Date: Thu, 21 Sep 2023 10:02:56 +0200 Subject: hwrng: stm32 - implement error concealment 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 Signed-off-by: Herbert Xu --- drivers/char/hw_random/stm32-rng.c | 114 +++++++++++++++++++++++++++++++++++-- 1 file changed, 110 insertions(+), 4 deletions(-) (limited to 'drivers/char') diff --git a/drivers/char/hw_random/stm32-rng.c b/drivers/char/hw_random/stm32-rng.c index 54bd5807bbac..adefe8edfd07 100644 --- a/drivers/char/hw_random/stm32-rng.c +++ b/drivers/char/hw_random/stm32-rng.c @@ -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 */ -- cgit v1.2.3