s390/crypto: use TRNG for seeding/reseeding
With the z14 machine there came also a CPACF hardware extension which provides a True Random Number Generator. This TRNG can be accessed with a new subfunction code within the CPACF prno instruction and provides random data with very high entropy. So if there is a TRNG available, let's use it for initial seeding and reseeding instead of the current implementation which tries to generate entropy based on stckf (store clock fast) jitters. For details about the amount of data needed and pulled for seeding and reseeding there can be explaining comments in the code found. Signed-off-by: Harald Freudenberger <freude@linux.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
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