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Subject[PATCH 3/3] hwrng: st: Use real-world device timings for timeout
Date
Samples are documented to be available every 0.667us, so in theory
the 8 sample deep FIFO should take 5.336us to fill. However, during
thorough testing, it became apparent that filling the FIFO actually
takes closer to 12us.

Signed-off-by: Lee Jones <lee.jones@linaro.org>
---
drivers/char/hw_random/st-rng.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/char/hw_random/st-rng.c b/drivers/char/hw_random/st-rng.c
index 44480fe..3b1432c 100644
--- a/drivers/char/hw_random/st-rng.c
+++ b/drivers/char/hw_random/st-rng.c
@@ -33,8 +33,13 @@
#define ST_RNG_FIFO_DEPTH 8
#define ST_RNG_FIFO_SIZE (ST_RNG_FIFO_DEPTH * ST_RNG_SAMPLE_SIZE)

-/* 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 8 sample deep FIFO should take 5.336us to fill. However, during
+ * thorough testing, it became apparent that filling the FIFO actually
+ * takes closer to 12us.
+ */
+#define ST_RNG_FILL_FIFO_TIMEOUT 12

struct st_rng_data {
void __iomem *base;
--
1.9.1


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