From 3537a855e3858b1f8b6cee545a22b8b67037235c Mon Sep 17 00:00:00 2001 From: Phil Elwell Date: Wed, 22 Mar 2023 15:30:38 +0000 Subject: [PATCH] hwrng: bcm2835 - sleep more intelligently While waiting for random data, use sleeps that are proportional to the amount of data expected. Prevent indefinite waits by giving up if nothing is received for a second. See: https://github.com/raspberrypi/linux/issues/5390 Signed-off-by: Phil Elwell --- drivers/char/hw_random/bcm2835-rng.c | 20 ++++++++++++++------ 1 file changed, 14 insertions(+), 6 deletions(-) --- a/drivers/char/hw_random/bcm2835-rng.c +++ b/drivers/char/hw_random/bcm2835-rng.c @@ -14,6 +14,7 @@ #include #include #include +#include #define RNG_CTRL 0x0 #define RNG_STATUS 0x4 @@ -28,6 +29,9 @@ #define RNG_INT_OFF 0x1 +#define RNG_FIFO_WORDS 4 +#define RNG_US_PER_WORD 34 /* Tuned for throughput */ + struct bcm2835_rng_priv { struct hwrng rng; void __iomem *base; @@ -64,19 +68,23 @@ static inline void rng_writel(struct bcm static int bcm2835_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait) { + u32 retries = 1000000/(RNG_FIFO_WORDS * RNG_US_PER_WORD); struct bcm2835_rng_priv *priv = to_rng_priv(rng); u32 max_words = max / sizeof(u32); u32 num_words, count; - while ((rng_readl(priv, RNG_STATUS) >> 24) == 0) { - if (!wait) + num_words = rng_readl(priv, RNG_STATUS) >> 24; + + while (!num_words) { + if (!wait || !retries) return 0; - hwrng_yield(rng); + retries--; + usleep_range((u32)RNG_US_PER_WORD, + (u32)RNG_US_PER_WORD * RNG_FIFO_WORDS); + num_words = rng_readl(priv, RNG_STATUS) >> 24; } - num_words = rng_readl(priv, RNG_STATUS) >> 24; - if (num_words > max_words) - num_words = max_words; + num_words = min(num_words, max_words); for (count = 0; count < num_words; count++) ((u32 *)buf)[count] = rng_readl(priv, RNG_DATA);