arm64: random: Add data to pool from setup_arch()

Since the arm64 ARCH_RANDOM implementation is not available until
cpufeature has determined the system capabilities it can't be used by
the generic random code to initialize the entropy pool for early use.
Instead explicitly add some data to the pool from setup_arch() if the
boot CPU supports v8.5-RNG, this is the point recommended by the generic
code.

Note that we are only adding data here, it will be mixed into the pool
but won't be credited as entropy. There are currently no suitable
interfaces for that at present - extending the random code to provide
those will be done as a future step. Providing data is better than not
doing so as it will still provide an increase in variation in the output
from the random code and there will be no impact on the rate at which
entropy is credited compared to what we have without this patch.

Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
2 files changed