Re: [PATCH v10 2/7] firmware: hwrng: arm_smccc_trng: Register as an SMCCC device
From: Jason Gunthorpe <jgg@nvidia.com>
Date: 2026-09-04 19:40:07
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linux-coco, lkml
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The SMCCC TRNG interface is a firmware-provided SMCCC service rather than a standalone platform device. Now that the SMCCC core has an SMCCC bus, create an arm-smccc-trng device for the discovered TRNG service and convert the hwrng driver to an SMCCC driver. The SMCCC id table preserves module autoloading for systems where the TRNG driver is built as a module. The sysfs device path changes from the old smccc_trng platform-device path to an arm-smccc device path. No known userspace dependency on the old path was found; a Debian Code Search lookup for the existing platform-device name/path did not find any users. Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> Tested-by: Andre Przywara <andre.przywara@arm.com> Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>diff --git a/arch/arm/include/asm/archrandom.h b/arch/arm/include/asm/archrandom.h index cc4714eb1a7556..ee39a03ddf8abe 100644 --- a/arch/arm/include/asm/archrandom.h +++ b/arch/arm/include/asm/archrandom.h@@ -2,7 +2,7 @@ #ifndef _ASM_ARCHRANDOM_H #define _ASM_ARCHRANDOM_H -static inline bool __init smccc_probe_trng(void) +static inline bool smccc_probe_trng(void) { return false; }
It is preexisting so Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> But I still think this is weird, and now looks weirder with a nice proper device driver. Inline this ARM64 version check code in the driver:
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diff --git a/arch/arm64/include/asm/archrandom.h b/arch/arm64/include/asm/archrandom.h index 8babfbe31f9541..7605dd81bd1e1f 100644 --- a/arch/arm64/include/asm/archrandom.h +++ b/arch/arm64/include/asm/archrandom.h@@ -12,7 +12,7 @@ extern bool smccc_trng_available; -static inline bool __init smccc_probe_trng(void) +static inline bool smccc_probe_trng(void) { struct arm_smccc_res res;
And adjust the kconfig to not permit the driver on ARM32 builds. Achieves the same outcome without involving arch code. Though I have no idea why it doesn't work on ARM32.
[ ... 108 lines skipped ... ] + if (IS_ENABLED(CONFIG_ARM) && ARM_SMCCC_IS_64(smccc_dev->func_id)) + return false;
This test passes for TRNG after all. -- Jason