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From:   Fabio Estevam <festevam@gmail.com>
To:     herbert@gondor.apana.org.au
Cc:     horia.geanta@nxp.com, gaurav.jain@nxp.com, V.Sethi@nxp.com,
        linux-crypto@vger.kernel.org, Fabio Estevam <festevam@denx.de>,
        stable@vger.kernel.org
Subject: [PATCH v5] crypto: caam - fix i.MX6SX entropy delay value
Date:   Wed, 20 Apr 2022 09:06:01 -0300
Message-Id: <20220420120601.1015362-1-festevam@gmail.com>
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Precedence: bulk

From: Fabio Estevam <festevam@denx.de>

Since commit 358ba762d9f1 ("crypto: caam - enable prediction resistance
in HRWNG") the following CAAM errors can be seen on i.MX6SX:

caam_jr 2101000.jr: 20003c5b: CCB: desc idx 60: RNG: Hardware error
hwrng: no data available

This error is due to an incorrect entropy delay for i.MX6SX.

Fix it by increasing the minimum entropy delay for i.MX6SX
as done in U-Boot:
https://patchwork.ozlabs.org/project/uboot/patch/20220415111049.2565744-1-gaurav.jain@nxp.com/

As explained in the U-Boot patch:

"RNG self tests are run to determine the correct entropy delay.
Such tests are executed with different voltages and temperatures to identify
the worst case value for the entropy delay. For i.MX6SX, it was determined
that after adding a margin value of 1000 the minimum entropy delay should be
at least 12000."

Cc: <stable@vger.kernel.org>
Fixes: 358ba762d9f1 ("crypto: caam - enable prediction resistance in HRWNG") 
Signed-off-by: Fabio Estevam <festevam@denx.de>
Reviewed-by: Horia Geantă <horia.geanta@nxp.com>
---
Changes since v4:
- Change the function name to needs_entropy_delay_adjustment() - Vabhav
- Improve the commit log by adding the explanation from the U-Boot
patch - Vabhav

 drivers/crypto/caam/ctrl.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/drivers/crypto/caam/ctrl.c b/drivers/crypto/caam/ctrl.c
index ca0361b2dbb0..f87aa2169e5f 100644
--- a/drivers/crypto/caam/ctrl.c
+++ b/drivers/crypto/caam/ctrl.c
@@ -609,6 +609,13 @@ static bool check_version(struct fsl_mc_version *mc_version, u32 major,
 }
 #endif
 
+static bool needs_entropy_delay_adjustment(void)
+{
+	if (of_machine_is_compatible("fsl,imx6sx"))
+		return true;
+	return false;
+}
+
 /* Probe routine for CAAM top (controller) level */
 static int caam_probe(struct platform_device *pdev)
 {
@@ -855,6 +862,8 @@ static int caam_probe(struct platform_device *pdev)
 			 * Also, if a handle was instantiated, do not change
 			 * the TRNG parameters.
 			 */
+			if (needs_entropy_delay_adjustment())
+				ent_delay = 12000;
 			if (!(ctrlpriv->rng4_sh_init || inst_handles)) {
 				dev_info(dev,
 					 "Entropy delay = %u\n",
@@ -871,6 +880,15 @@ static int caam_probe(struct platform_device *pdev)
 			 */
 			ret = instantiate_rng(dev, inst_handles,
 					      gen_sk);
+			/*
+			 * Entropy delay is determined via TRNG characterization.
+			 * TRNG characterization is run across different voltages
+			 * and temperatures.
+			 * If worst case value for ent_dly is identified,
+			 * the loop can be skipped for that platform.
+			 */
+			if (needs_entropy_delay_adjustment())
+				break;
 			if (ret == -EAGAIN)
 				/*
 				 * if here, the loop will rerun,
-- 
2.25.1