diff options
Diffstat (limited to 'drivers/char/hw_random/st-rng.c')
| -rw-r--r-- | drivers/char/hw_random/st-rng.c | 10 |
1 files changed, 8 insertions, 2 deletions
diff --git a/drivers/char/hw_random/st-rng.c b/drivers/char/hw_random/st-rng.c index 8c8a435176e8..17f0a092bf24 100644 --- a/drivers/char/hw_random/st-rng.c +++ b/drivers/char/hw_random/st-rng.c @@ -32,8 +32,14 @@ #define ST_RNG_FIFO_SIZE 8 #define ST_RNG_SAMPLE_SIZE 2 /* 2 Byte (16bit) samples */ -/* Samples are available every 0.667us, which we round to 1us */ -#define ST_RNG_FILL_FIFO_TIMEOUT (1 * (ST_RNG_FIFO_SIZE / ST_RNG_SAMPLE_SIZE)) +/* + * Samples are documented to be available every 0.667us, so in theory + * the 4 sample deep FIFO should take 2.668us to fill. However, during + * thorough testing, it became apparent that filling the FIFO actually + * takes closer to 12us. We then multiply by 2 in order to account for + * the lack of udelay()'s reliability, suggested by Russell King. + */ +#define ST_RNG_FILL_FIFO_TIMEOUT (12 * 2) struct st_rng_data { void __iomem *base; |