linux-kernel - Re: [PATCH v2 5/7] hwrng: exynos: Add SMC based TRNG operation

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Message-ID: <oypijdbk3vu3qd.fsf%l.stelmach@samsung.com>
Date: Thu, 20 Jun 2024 15:46:02 +0200
From: Lukasz Stelmach <l.stelmach@...sung.com>
To: Sam Protsenko <semen.protsenko@...aro.org>
Cc: Krzysztof Kozlowski <krzk+dt@...nel.org>,  Rob Herring
	<robh@...nel.org>,  Conor Dooley <conor+dt@...nel.org>,  Anand Moon
	<linux.amoon@...il.com>,  Olivia Mackall <olivia@...enic.com>,  Herbert Xu
	<herbert@...dor.apana.org.au>,  Alim Akhtar <alim.akhtar@...sung.com>,
	linux-samsung-soc@...r.kernel.org,  linux-crypto@...r.kernel.org,
	devicetree@...r.kernel.org,  linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 5/7] hwrng: exynos: Add SMC based TRNG operation

It was <2024-06-18 wto 15:45>, when Sam Protsenko wrote:
> On some Exynos chips like Exynos850 the access to Security Sub System
> (SSS) registers is protected with TrustZone, and therefore only possible
> from EL3 monitor software. The Linux kernel is running in EL1, so the
> only way for the driver to obtain TRNG data is via SMC calls to EL3
> monitor. Implement such SMC operation and use it when EXYNOS_SMC flag is
> set in the corresponding chip driver data.
>
> Signed-off-by: Sam Protsenko <semen.protsenko@...aro.org>
> Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
> ---
> Changes in v2:
>   - Used the "reversed Christmas tree" style in the variable declaration
>     block in exynos_trng_do_read_smc()
>   - Renamed .quirks to .flags in the driver structure
>   - Added Krzysztof's R-b tag
>
>  drivers/char/hw_random/exynos-trng.c | 133 +++++++++++++++++++++++++--
>  1 file changed, 123 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/char/hw_random/exynos-trng.c b/drivers/char/hw_random/exynos-trng.c
> index 99a0b271ffb7..497d6018c6ba 100644
> --- a/drivers/char/hw_random/exynos-trng.c
> +++ b/drivers/char/hw_random/exynos-trng.c
> @@ -10,6 +10,7 @@
>   * Krzysztof Kozłowski <krzk@...nel.org>
>   */

[...]

> +static int exynos_trng_init_smc(struct hwrng *rng)
> +{
> +	struct arm_smccc_res res;
> +
> +	arm_smccc_smc(SMC_CMD_RANDOM, HWRNG_INIT, 0, 0, 0, 0, 0, 0, &res);
> +	if (res.a0 != HWRNG_RET_OK)
> +		return -EIO;
> +
> +	return 0;
> +}
> +

Does this driver requiers some vendor-specifig bootloading code?
I am testing the code on a WinLink E850-96 board booted with the
upstream u-boot and it fails during init (res0.a is -1).

[    1.883413] exynos-trng 12081400.rng: Could not register hwrng device
[    1.893394] exynos-trng 12081400.rng: probe with driver exynos-trng failed with error -5

If an additional code outside the kernel is required for this to run,
then maybe the error message should reflect that.

Kind regards,
-- 
Łukasz Stelmach
Samsung R&D Institute Poland
Samsung Electronics

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