[PATCH] hwrng: airoha set rng quality to 900

[Aleksander Jan Bajkowski]

Airoha uses RAW mode to collect noise from the TRNG. These appear to
be unprocessed oscillations from the tero loop. For this reason, they
do not have a perfect distribution and entropy. Simple noise compression
reduces its size by 9%, so setting the quality to 900 seems reasonable.
The same value is used by the downstream driver.

Compare the size before and after compression:
$ ls -l random_airoha*
-rw-r--r-- 1 aleksander aleksander 76546048 Jan  3 23:43 random_airoha
-rw-rw-r-- 1 aleksander aleksander 69783562 Jan  5 20:23 random_airoha.zip

FIPS test results:
$ cat random_airoha | rngtest -c 10000
rngtest 2.6
Copyright (c) 2004 by Henrique de Moraes Holschuh
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

rngtest: starting FIPS tests...
rngtest: bits received from input: 200000032
rngtest: FIPS 140-2 successes: 0
rngtest: FIPS 140-2 failures: 10000
rngtest: FIPS 140-2(2001-10-10) Monobit: 9957
rngtest: FIPS 140-2(2001-10-10) Poker: 10000
rngtest: FIPS 140-2(2001-10-10) Runs: 10000
rngtest: FIPS 140-2(2001-10-10) Long run: 4249
rngtest: FIPS 140-2(2001-10-10) Continuous run: 0
rngtest: input channel speed: (min=953.674; avg=27698.935; max=19073.486)Mibits/s
rngtest: FIPS tests speed: (min=59.791; avg=298.028; max=328.853)Mibits/s
rngtest: Program run time: 647638 microseconds

In general, these data look like real noise, but with lower entropy
than expected.

Fixes: e53ca8efcc5e ("hwrng: airoha - add support for Airoha EN7581 TRNG")
Suggested-by: Benjamin Larsson <benjamin.larsson@xxxxxxxxxx>
Signed-off-by: Aleksander Jan Bajkowski <olek2@xxxxx>
---
 drivers/char/hw_random/airoha-trng.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/char/hw_random/airoha-trng.c b/drivers/char/hw_random/airoha-trng.c
index 1dbfa9505c21..9a648f6d9fd4 100644
--- a/drivers/char/hw_random/airoha-trng.c
+++ b/drivers/char/hw_random/airoha-trng.c
@@ -212,6 +212,7 @@ static int airoha_trng_probe(struct platform_device *pdev)
 	trng->rng.init = airoha_trng_init;
 	trng->rng.cleanup = airoha_trng_cleanup;
 	trng->rng.read = airoha_trng_read;
+	trng->rng.quality = 900;
 
 	ret = devm_hwrng_register(dev, &trng->rng);
 	if (ret) {
-- 
2.47.3