Re: [PATCH v14 06/44] arm64: RMI: Check for RMI support at init

[Gavin Shan <gshan@redhat.com>]

Hi Steven,

On 5/13/26 11:17 PM, Steven Price wrote:
> Query the RMI version number and check if it is a compatible version.
> The first two feature registers are read and exposed for future code to
> use.
> 
> Signed-off-by: Steven Price <steven.price@arm.com>
> ---
> v14:
>   * This moves the basic RMI setup into the 'kernel' directory. This is
>     because RMI will be used for some features outside of KVM so should
>     be available even if KVM isn't compiled in.
> ---
>   arch/arm64/include/asm/rmi_cmds.h |  3 ++
>   arch/arm64/kernel/Makefile        |  2 +-
>   arch/arm64/kernel/cpufeature.c    |  1 +
>   arch/arm64/kernel/rmi.c           | 65 +++++++++++++++++++++++++++++++
>   4 files changed, 70 insertions(+), 1 deletion(-)
>   create mode 100644 arch/arm64/kernel/rmi.c
> 

[...]

> diff --git a/arch/arm64/kernel/rmi.c b/arch/arm64/kernel/rmi.c
> new file mode 100644
> index 000000000000..99c1ccc35c11
> --- /dev/null
> +++ b/arch/arm64/kernel/rmi.c
> @@ -0,0 +1,65 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2023-2025 ARM Ltd.
> + */
> +
> +#include <linux/memblock.h>
> +
> +#include <asm/rmi_cmds.h>
> +
> +unsigned long rmm_feat_reg0;
> +unsigned long rmm_feat_reg1;
> +
> +static int rmi_check_version(void)
> +{
> +	struct arm_smccc_res res;
> +	unsigned short version_major, version_minor;
> +	unsigned long host_version = RMI_ABI_VERSION(RMI_ABI_MAJOR_VERSION,
> +						     RMI_ABI_MINOR_VERSION);
> +	unsigned long aa64pfr0 = read_sanitised_ftr_reg(SYS_ID_AA64PFR0_EL1);
> +
> +	/* If RME isn't supported, then RMI can't be */
> +	if (cpuid_feature_extract_unsigned_field(aa64pfr0, ID_AA64PFR0_EL1_RME_SHIFT) == 0)
> +		return -ENXIO;
> +
> +	arm_smccc_1_1_invoke(SMC_RMI_VERSION, host_version, &res);
> +
> +	if (res.a0 == SMCCC_RET_NOT_SUPPORTED)
> +		return -ENXIO;
> +
> +	version_major = RMI_ABI_VERSION_GET_MAJOR(res.a1);
> +	version_minor = RMI_ABI_VERSION_GET_MINOR(res.a1);
> +
> +	if (res.a0 != RMI_SUCCESS) {
> +		unsigned short high_version_major, high_version_minor;
> +
> +		high_version_major = RMI_ABI_VERSION_GET_MAJOR(res.a2);
> +		high_version_minor = RMI_ABI_VERSION_GET_MINOR(res.a2);
> +
> +		pr_err("Unsupported RMI ABI (v%d.%d - v%d.%d) we want v%d.%d\n",
> +		       version_major, version_minor,
> +		       high_version_major, high_version_minor,
> +		       RMI_ABI_MAJOR_VERSION,
> +		       RMI_ABI_MINOR_VERSION);
> +		return -ENXIO;
> +	}
> +
> +	pr_info("RMI ABI version %d.%d\n", version_major, version_minor);
> +
> +	return 0;
> +}
> +
> +static int __init arm64_init_rmi(void)
> +{
> +	/* Continue without realm support if we can't agree on a version */
> +	if (rmi_check_version())
> +		return 0;

Is this still a valid point that we have to return zero on errors returned
from rmi_check_version() or other other function calls like rmi_features()?
arm64_init_rmi() is triggered by subsys_initcall() where the return value
needs to indicate success or failure. It's fine to return error code from
arm64_init_rmi() in the path.

> +
> +	if (WARN_ON(rmi_features(0, &rmm_feat_reg0)))
> +		return 0;
> +	if (WARN_ON(rmi_features(1, &rmm_feat_reg1)))
> +		return 0;
> +
> +	return 0;
> +}
> +subsys_initcall(arm64_init_rmi);

Thanks,
Gavin