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Re: [PATCH 3/3] hwrng: st: Use real-world device timings for timeout

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On Tue, Oct 06, 2015 at 03:44:00PM +0100, Lee Jones wrote:
> 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.

Is that measured?

> +/*
> + * 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

I hope you're not using such a precise figure with udelay().  udelay()
is not guaranteed to give exactly (or even at least) the delay you
request.  It's defined to give an approximate delay.

Many people have a problem understanding that, so I won't explain why
it is that way, just accept that it is and move on... it's not going
to magically get "fixed" because someone has just learnt about this. :)

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[RESEND 1/3] hwrng: st: dt: Fix trivial typo in node address Lee Jones <lee.jones@linaro.org> - 2015-10-06 16:50 +0200
  [PATCH 3/3] hwrng: st: Use real-world device timings for timeout Lee Jones <lee.jones@linaro.org> - 2015-10-06 16:50 +0200
    Re: [PATCH 3/3] hwrng: st: Use real-world device timings for timeout Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-10-06 21:40 +0200
      Re: [PATCH 3/3] hwrng: st: Use real-world device timings for timeout Russell King - ARM Linux <linux@arm.linux.org.uk> - 2015-10-06 23:00 +0200
        Re: [PATCH 3/3] hwrng: st: Use real-world device timings for timeout Lee Jones <lee.jones@linaro.org> - 2015-10-07 10:00 +0200
      Re: [PATCH 3/3] hwrng: st: Use real-world device timings for timeout Lee Jones <lee.jones@linaro.org> - 2015-10-06 23:00 +0200
  Re: [RESEND 1/3] hwrng: st: dt: Fix trivial typo in node address Herbert Xu <herbert@gondor.apana.org.au> - 2015-10-06 17:40 +0200

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