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

[Gavin Shan <gshan@redhat.com>]

On 10/13/26 7:58 PM, Suzuki K Poulose wrote:
> On 13/10/2026 04:53, Gavin Shan wrote:
>> 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)
> 
> We could. But I am wondering if that adds any value ? If the RMM
> exists and responds to the RMI_ABI_VERSION, it must be so on a
> platform with v1.2 or greater ? The extra check doesn't hurt.
> 

It's required as documented in section "B1.1 overview" of RMM-spec-v2.0-bet3.
In the same section, there are more requirements regarding the SMCCC version
when SVE/SME are supported. I don't see a practical problem if the check is
missed since the combination of TF-A and TF-RMM are the only RMM-spec-v2.0-bet3
implementation (as I knew) where the SMCCC version has been set to v1.5 in the
'master' branch.

Thanks,
Gavin

> Suzuki
> 
>>          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;
>>> +}
>>> +
>>
>> [...]
>>
>>
>>
>