[PATCH v2 1/6] crypto: caam - RNG4 TRNG errata

[Andrey Smirnov]

The TRNG as used in RNG4, used in CAAM has a documentation issue. The
effect is that it is possible that the entropy used to instantiate the
DRBG may be old entropy, rather than newly generated entropy. There is
proper programming guidance, but it is not in the documentation.

Signed-off-by: Aymen Sghaier <aymen.sghaier@xxxxxxx>
Signed-off-by: Vipul Kumar <vipul_kumar@xxxxxxxxxx>
[andrew.smirnov@xxxxxxxxx ported to upstream kernel]
Signed-off-by: Andrey Smirnov <andrew.smirnov@xxxxxxxxx>
Cc: Chris Healy <cphealy@xxxxxxxxx>
Cc: Lucas Stach <l.stach@xxxxxxxxxxxxxx>
Cc: Horia GeantÄ <horia.geanta@xxxxxxx>
Cc: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Cc: Iuliana Prodan <iuliana.prodan@xxxxxxx>
Cc: linux-crypto@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: linux-imx@xxxxxxx
---
 drivers/crypto/caam/ctrl.c | 11 ++++++++---
 drivers/crypto/caam/regs.h |  3 ++-
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/drivers/crypto/caam/ctrl.c b/drivers/crypto/caam/ctrl.c
index d7c3c3805693..df4db10e9fca 100644
--- a/drivers/crypto/caam/ctrl.c
+++ b/drivers/crypto/caam/ctrl.c
@@ -338,8 +338,12 @@ static void kick_trng(struct platform_device *pdev, int ent_delay)
 	ctrl = (struct caam_ctrl __iomem *)ctrlpriv->ctrl;
 	r4tst = &ctrl->r4tst[0];
 
-	/* put RNG4 into program mode */
-	clrsetbits_32(&r4tst->rtmctl, 0, RTMCTL_PRGM);
+	/*
+	 * Setting both RTMCTL:PRGM and RTMCTL:TRNG_ACC causes TRNG to
+	 * properly invalidate the entropy in the entropy register and
+	 * force re-generation.
+	 */
+	clrsetbits_32(&r4tst->rtmctl, 0, RTMCTL_PRGM | RTMCTL_ACC);
 
 	/*
 	 * Performance-wise, it does not make sense to
@@ -369,7 +373,8 @@ static void kick_trng(struct platform_device *pdev, int ent_delay)
 	 * select raw sampling in both entropy shifter
 	 * and statistical checker; ; put RNG4 into run mode
 	 */
-	clrsetbits_32(&r4tst->rtmctl, RTMCTL_PRGM, RTMCTL_SAMP_MODE_RAW_ES_SC);
+	clrsetbits_32(&r4tst->rtmctl, RTMCTL_PRGM | RTMCTL_ACC,
+		      RTMCTL_SAMP_MODE_RAW_ES_SC);
 }
 
 static int caam_get_era_from_hw(struct caam_ctrl __iomem *ctrl)
diff --git a/drivers/crypto/caam/regs.h b/drivers/crypto/caam/regs.h
index 05127b70527d..c191e8fd0fa7 100644
--- a/drivers/crypto/caam/regs.h
+++ b/drivers/crypto/caam/regs.h
@@ -487,7 +487,8 @@ struct rngtst {
 
 /* RNG4 TRNG test registers */
 struct rng4tst {
-#define RTMCTL_PRGM	0x00010000	/* 1 -> program mode, 0 -> run mode */
+#define RTMCTL_ACC  BIT(5)  /* TRNG access mode */
+#define RTMCTL_PRGM BIT(16) /* 1 -> program mode, 0 -> run mode */
 #define RTMCTL_SAMP_MODE_VON_NEUMANN_ES_SC	0 /* use von Neumann data in
 						     both entropy shifter and
 						     statistical checker */
-- 
2.21.0