linux-kernel - [PATCH] hwrng: airoha set rng quality to 900

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Message-ID: <20260105204204.2430571-1-olek2@wp.pl>
Date: Mon,  5 Jan 2026 21:41:49 +0100
From: Aleksander Jan Bajkowski <olek2@...pl>
To: benjamin.larsson@...exis.eu,
	olivia@...enic.com,
	herbert@...dor.apana.org.au,
	olek2@...pl,
	martin@...ser.cx,
	ansuelsmth@...il.com,
	linux-crypto@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] hwrng: airoha set rng quality to 900

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@...exis.eu>
Signed-off-by: Aleksander Jan Bajkowski <olek2@...pl>
---
 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