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Date:   Tue, 19 Apr 2022 13:27:45 +0300
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Subject: Re: [PATCH v3] crypto: caam - fix i.MX6SX entropy delay value
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To:     Fabio Estevam <festevam@gmail.com>,
        "herbert@gondor.apana.org.au" <herbert@gondor.apana.org.au>
Cc:     Gaurav Jain <gaurav.jain@nxp.com>, Varun Sethi <V.Sethi@nxp.com>,
        "linux-crypto@vger.kernel.org" <linux-crypto@vger.kernel.org>,
        Fabio Estevam <festevam@denx.de>
References: <20220418122728.203919-1-festevam@gmail.com>
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On 4/18/2022 3:27 PM, Fabio Estevam wrote:
> 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
> caam_jr 2101000.jr: 20003c5b: CCB: desc idx 60: RNG: Hardware error
> 
> 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/
> 
> Fixes: 358ba762d9f1 ("crypto: caam - enable prediction resistance in HRWNG") 
> Signed-off-by: Fabio Estevam <festevam@denx.de>
> ---
> Changes since v2:
> - Added Fixes tag. (Horia)
> 
> Change since v1:
> - Align the fix with U-Boot.
> 
>  drivers/crypto/caam/ctrl.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/drivers/crypto/caam/ctrl.c b/drivers/crypto/caam/ctrl.c
> index ca0361b2dbb0..c515c20442d5 100644
> --- a/drivers/crypto/caam/ctrl.c
> +++ b/drivers/crypto/caam/ctrl.c
> @@ -648,6 +648,8 @@ static int caam_probe(struct platform_device *pdev)
>  			return ret;
>  	}
>  
> +	if (of_machine_is_compatible("fsl,imx6sx"))
> +		ent_delay = 12000;
>  
This looks rather randomly placed in the probe() function.
I'd suggest moving it into the RNG initialization area.
Another benefit would be calling of_machine_is_compatible() only once.

>  	/* Get configuration properties from device tree */
>  	/* First, get register page */
> @@ -871,6 +873,15 @@ static int caam_probe(struct platform_device *pdev)
>  			 */
>  			ret = instantiate_rng(dev, inst_handles,
>  					      gen_sk);
> +			/*
> +			 * Entropy delay is calculated via self-test method.
> +			 * Self-test is run across different voltages and
> +			 * temperatures.
A clarification wrt. terminology:
-"self-tests" refer to HW checks done when initializing the RNG
(instantiating the RNG state handle), they are statistical tests to check
the quality of the entropy
-"TRNG characterization" is the offline process of determining the entropy delay
values that are "suitable" - i.e. allowing TRNG to work correctly across
ranges of temperature, voltage and clock frequency

> +			 * If worst case value for ent_dly is identified,
> +			 * the loop can be skipped for that platform.
> +			 */
> +			if (of_machine_is_compatible("fsl,imx6sx"))
> +				break;
>  			if (ret == -EAGAIN)
>  				/*
>  				 * if here, the loop will rerun,

Thanks,
Horia