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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 v4] crypto: caam - fix i.MX6SX entropy delay value
Date:   Tue, 19 Apr 2022 08:44:44 -0300
Message-Id: <20220419114444.586113-1-festevam@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
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/

Cc: <stable@vger.kernel.org>
Fixes: 358ba762d9f1 ("crypto: caam - enable prediction resistance in HRWNG") 
Signed-off-by: Fabio Estevam <festevam@denx.de>
---
Changes since v3:
- Add a needs_extended_entropy_delay() function
- Assign the 'ent_delay' inside the the RNG initialization area. (Horia)
- Change the terminology as per Horia's explanation.

 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..5b989a842ee9 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_extended_entropy_delay(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_extended_entropy_delay())
+				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_extended_entropy_delay())
+				break;
 			if (ret == -EAGAIN)
 				/*
 				 * if here, the loop will rerun,
-- 
2.25.1