iMX6D CAAM RNG problems in v5.10.1

[Robert Hancock <robert.hancock@calian.com>]

Hello,

We have an iMX6D-based board which was previously using 5.4.x kernels.
I have recently started testing v5.10.1 on this board and am running
into an issue with the CAAM RNG. The dmesg is getting output like this
and all reads from /dev/hwrng are failing with EINVAL:

[   17.368368] caam_jr 2101000.jr: 2000025b: CCB: desc idx 2: RNG:
Hardware error
[   17.375721] hwrng: no data available
[   23.200255] caam_jr 2101000.jr: 20003c5b: CCB: desc idx 60: RNG:
Hardware error
[   23.215508] caam_jr 2101000.jr: 20003c5b: CCB: desc idx 60: RNG:
Hardware error
[   23.229249] caam_jr 2101000.jr: 20003c5b: CCB: desc idx 60: RNG:
Hardware error
[   23.243415] caam_jr 2101000.jr: 20003c5b: CCB: desc idx 60: RNG:
Hardware error
[   23.257809] caam_jr 2101000.jr: 20003c5b: CCB: desc idx 60: RNG:
Hardware error
[   23.272109] caam_jr 2101000.jr: 20003c5b: CCB: desc idx 60: RNG:
Hardware error

We are not using secure boot presently, if that matters. On 5.4, no
such issues and /dev/hwrng seems to work fine.

I see there are some CAAM RNG changes between 5.4 and 5.10 but not sure
which might be the cause?

The CAAM initialization output on boot (same on working 5.4 and non-
working 5.10.1 kernels):

[   16.934253] caam 2100000.crypto: Entropy delay = 3200
[   17.000146] caam 2100000.crypto: Instantiated RNG4 SH0
[   17.060911] caam 2100000.crypto: Instantiated RNG4 SH1
[   17.067891] caam 2100000.crypto: device ID = 0x0a16010000000000 (Era
4)
[   17.080289] caam 2100000.crypto: job rings = 2, qi = 0
[   17.113498] caam algorithms registered in /proc/crypto
[   17.120099] caam 2100000.crypto: registering rng-caam

-- 
Robert Hancock
Senior Hardware Designer, Calian Advanced Technologies
www.calian.com