On Mon, Oct 14, 2019 at 05:32:45PM +0530, Sumit Garg wrote:
> Existing RNG data read timeout is 200us but it doesn't cover EIP76 RNG
> data rate which takes approx. 700us to produce 16 bytes of output data
> as per testing results. So configure the timeout as 1000us to also take
> account of lack of udelay()'s reliability.
What "lack of udelay()'s reliability" are you concerned about?
Daniel.
>
> Fixes: 383212425c92 ("hwrng: omap - Add device variant for SafeXcel IP-76 found in Armada 8K")
> Cc: <stable@xxxxxxxxxxxxxxx>
> Signed-off-by: Sumit Garg <sumit.garg@xxxxxxxxxx>
> ---
> drivers/char/hw_random/omap-rng.c | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/char/hw_random/omap-rng.c b/drivers/char/hw_random/omap-rng.c
> index b27f396..e329f82 100644
> --- a/drivers/char/hw_random/omap-rng.c
> +++ b/drivers/char/hw_random/omap-rng.c
> @@ -66,6 +66,13 @@
> #define OMAP4_RNG_OUTPUT_SIZE 0x8
> #define EIP76_RNG_OUTPUT_SIZE 0x10
>
> +/*
> + * EIP76 RNG takes approx. 700us to produce 16 bytes of output data
> + * as per testing results. And to account for the lack of udelay()'s
> + * reliability, we keep the timeout as 1000us.
> + */
> +#define RNG_DATA_FILL_TIMEOUT 100
> +
> enum {
> RNG_OUTPUT_0_REG = 0,
> RNG_OUTPUT_1_REG,
> @@ -176,7 +183,7 @@ static int omap_rng_do_read(struct hwrng *rng, void *data, size_t max,
> if (max < priv->pdata->data_size)
> return 0;
>
> - for (i = 0; i < 20; i++) {
> + for (i = 0; i < RNG_DATA_FILL_TIMEOUT; i++) {
> present = priv->pdata->data_present(priv);
> if (present || !wait)
> break;
> --
> 2.7.4
>
