[PATCH v6 7/7] crypto: caam - limit single JD RNG output to maximum of 16 bytes

[Andrey Smirnov <andrew.smirnov@gmail.com>]

In order to follow recommendation in SP800-90C (section "9.4 The
Oversampling-NRBG Construction") limit the output of "generate" JD
submitted to CAAM. See
https://lore.kernel.org/linux-crypto/VI1PR0402MB3485EF10976A4A69F90E5B0F98580@VI1PR0402MB3485.eurprd04.prod.outlook.com/
for more details.

This change should make CAAM's hwrng driver good enough to have 999
quality rating.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Cc: Chris Healy <cphealy@gmail.com>
Cc: Lucas Stach <l.stach@pengutronix.de>
Cc: Horia Geantă <horia.geanta@nxp.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Iuliana Prodan <iuliana.prodan@nxp.com>
Cc: linux-crypto@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-imx@nxp.com
---
 drivers/crypto/caam/caamrng.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/crypto/caam/caamrng.c b/drivers/crypto/caam/caamrng.c
index 91ccde0240fe..2b75ffffcac9 100644
--- a/drivers/crypto/caam/caamrng.c
+++ b/drivers/crypto/caam/caamrng.c
@@ -23,7 +23,7 @@
 #include "error.h"
 
 /* length of descriptors */
-#define CAAM_RNG_MAX_FIFO_STORE_SIZE	U16_MAX
+#define CAAM_RNG_MAX_FIFO_STORE_SIZE	16
 
 #define CAAM_RNG_FIFO_LEN		SZ_32K /* Must be a multiple of 2 */
 
@@ -134,7 +134,7 @@ static void caam_rng_fill_async(struct caam_rng_ctx *ctx)
 
 	sg_init_table(sg, ARRAY_SIZE(sg));
 	nents = kfifo_dma_in_prepare(&ctx->fifo, sg, ARRAY_SIZE(sg),
-				     CAAM_RNG_FIFO_LEN);
+				     CAAM_RNG_MAX_FIFO_STORE_SIZE);
 	if (!nents)
 		return;
 
@@ -241,6 +241,7 @@ int caam_rng_init(struct device *ctrldev)
 	ctx->rng.init    = caam_init;
 	ctx->rng.cleanup = caam_cleanup;
 	ctx->rng.read    = caam_read;
+	ctx->rng.quality = 999;
 
 	dev_info(ctrldev, "registering rng-caam\n");
 
-- 
2.21.0