Re: [PATCH v22 02/10] firmware: arm_rmm: Check for RMI support at init

[Gavin Shan <gshan@redhat.com>]

Hi Suzuki,

On 10/2/26 4:14 PM, Suzuki K Poulose wrote:
> From: Steven Price <steven.price@arm.com>
> 
> Query the RMI version number and check if it is a compatible version.
> All RMM feature registers are read and exposed for future code to
> use. Also restrict the support to SMC conduit.
> 
> We only support this for Little Endian kernels, the Big Endian kernel
> support is anyway marked BROKEN and is being removed.
> 
> Cc: Marc Zyngier <maz@kernel.org>
> Cc: Oliver Upton <oupton@kernel.org>
> Reviewed-by: Jonathan Cameron <jonathan.cameron@oss.qualcomm.com>
> Reviewed-by: Gavin Shan <gshan@redhat.com>
> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
> Tested-by: Gavin Shan <gshan@redhat.com>
> Signed-off-by: Steven Price <steven.price@arm.com>
> Co-developed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> ---

[...]

> ---
>   MAINTAINERS                       |   2 +
>   arch/arm64/Kconfig                |   1 +
>   arch/arm64/kernel/cpufeature.c    |   1 +
>   arch/arm64/kvm/sys_regs.c         |   2 +
>   drivers/firmware/Kconfig          |   1 +
>   drivers/firmware/Makefile         |   1 +
>   drivers/firmware/arm_rmm/Kconfig  |  25 +++++++
>   drivers/firmware/arm_rmm/Makefile |   1 +
>   drivers/firmware/arm_rmm/rmi.c    | 112 ++++++++++++++++++++++++++++++
>   include/linux/arm-rmi-cmds.h      |  48 +++++++++++++
>   10 files changed, 194 insertions(+)
>   create mode 100644 drivers/firmware/arm_rmm/Kconfig
>   create mode 100644 drivers/firmware/arm_rmm/Makefile
>   create mode 100644 drivers/firmware/arm_rmm/rmi.c
>   create mode 100644 include/linux/arm-rmi-cmds.h
> 

[...]

> diff --git a/drivers/firmware/arm_rmm/rmi.c b/drivers/firmware/arm_rmm/rmi.c
> new file mode 100644
> index 0000000000000..06f5392c982d2
> --- /dev/null
> +++ b/drivers/firmware/arm_rmm/rmi.c
> @@ -0,0 +1,112 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2023-2026 ARM Ltd.
> + */
> +
> +#include <linux/arm-rmi-cmds.h>
> +#include <linux/cpufeature.h>
> +#include <linux/memblock.h>
> +#include <linux/slab.h>
> +
> +#include <asm/memory.h>
> +#include <asm/pgtable-hwdef.h>
> +
> +/* RMM v2.0 defines RmiFeatureRegister0 to RmiFeatureRegister4. */
> +static unsigned long rmi_feat_reg_cache[5] __ro_after_init;
> +
> +static int rmi_check_version(void)
> +{
> +	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);
> +	struct arm_smccc_1_2_regs res = {
> +		SMC_RMI_VERSION, host_version,
> +	};
> +
> +	/* 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;
> +
> +	if (arm_smccc_1_1_get_conduit() != SMCCC_CONDUIT_SMC)
> +		return -ENXIO;

I think we need to ensure SMCCC version is v1.2 or a newer one here? arm_smccc_1_2_smc()
is immediately called by rmi_smccc_invoke() after this check.

	if (arm_smccc_1_1_get_conduit() != SMCCC_CONDUIT_SMC ||
             arm_smccc_get_version() < ARM_SMCCC_VERSION_1_2)
		return -ENXIO;

Thanks,
Gavin

> +
> +	rmi_smccc_invoke(&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;
> +}
> +

[...]