On Sun 2019-10-06 11:06:38, Linus Torvalds wrote: > On Sun, Oct 6, 2019 at 10:35 AM Pavel Machek <pa...@ucw.cz> wrote: > > > > It will not: boot is now halted because systemd wants some > > entropy. Everything is idle and very little interrupts are > > happening. We have spinning rust, but it is idle, and thus not > > generating any interrupts. > > Yes, but we have that problem now solved. > > Except on embedded platforms that have garbage CPU's without even a > cycle counter. > > But those won't have spinning rust anyway. > > Yes, bad SSD's and MMC disks (that they do have) will generate timing > noise too, but in the absense of a cycle counter, that noise won't be > much use.
Even without cycle counter... if we _know_ we are trying to generate
entropy and have MMC available, we don't care about power and
performance.
So we can just...
issue read request on MMC
while (!interrupt_done)
i++
...and then use i++ as poor man's version of cycle counter.
[We would not want to do that in normal operation, for obvious
reasons, just when userland is blocked and waiting for entropy.]
Hmm?
Best regards,
Pavel
--
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