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Date: Fri, 1 May 2020 16:07:39 +0100
From: Steven Price <steven.price@....com>
To: Sudeep Holla <sudeep.holla@....com>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>
Cc: Catalin Marinas <Catalin.Marinas@....com>,
Will Deacon <will@...nel.org>,
Mark Rutland <Mark.Rutland@....com>,
Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"Harb Abdulhamid (harb@...erecomputing.com)"
<harb@...erecomputing.com>
Subject: Re: [PATCH 5/5] arm/arm64: smccc: Add ARCH_SOC_ID support
On 30/04/2020 12:48, Sudeep Holla wrote:
> SMCCC v1.2 adds a new optional function SMCCC_ARCH_SOC_ID to obtain a
> SiP defined SoC identification value. Add support for the same.
>
> Also using the SoC bus infrastructure, let us expose the platform
> specific SoC atrributes under sysfs. We also provide custom sysfs for
> the vendor ID as JEP-106 bank and identification code.
>
> Signed-off-by: Sudeep Holla <sudeep.holla@....com>
> ---
> drivers/firmware/psci/Makefile | 2 +-
> drivers/firmware/psci/soc_id.c | 148 +++++++++++++++++++++++++++++++++
> include/linux/arm-smccc.h | 5 ++
> 3 files changed, 154 insertions(+), 1 deletion(-)
> create mode 100644 drivers/firmware/psci/soc_id.c
>
> diff --git a/drivers/firmware/psci/Makefile b/drivers/firmware/psci/Makefile
> index 1956b882470f..c0b0c9ca57e4 100644
> --- a/drivers/firmware/psci/Makefile
> +++ b/drivers/firmware/psci/Makefile
> @@ -1,4 +1,4 @@
> # SPDX-License-Identifier: GPL-2.0
> #
> -obj-$(CONFIG_ARM_PSCI_FW) += psci.o
> +obj-$(CONFIG_ARM_PSCI_FW) += psci.o soc_id.o
> obj-$(CONFIG_ARM_PSCI_CHECKER) += psci_checker.o
> diff --git a/drivers/firmware/psci/soc_id.c b/drivers/firmware/psci/soc_id.c
> new file mode 100644
> index 000000000000..820f69dad7f5
> --- /dev/null
> +++ b/drivers/firmware/psci/soc_id.c
> @@ -0,0 +1,148 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright 2020 Arm Limited
> + */
> +
> +#include <linux/arm-smccc.h>
> +#include <linux/bitfield.h>
> +#include <linux/device.h>
> +#include <linux/module.h>
> +#include <linux/kernel.h>
> +#include <linux/slab.h>
> +#include <linux/sys_soc.h>
> +
> +#define SOCID_JEP106_BANK_IDX_MASK GENMASK(30, 24)
> +#define SOCID_JEP106_ID_CODE_MASK GENMASK(23, 16)
> +#define SOCID_IMP_DEF_SOC_ID_MASK GENMASK(15, 0)
> +#define JEP106_BANK_IDX(x) (u8)(FIELD_GET(SOCID_JEP106_BANK_IDX_MASK, (x)))
> +#define JEP106_ID_CODE(x) (u8)(FIELD_GET(SOCID_JEP106_ID_CODE_MASK, (x)))
> +#define IMP_DEF_SOC_ID(x) (u16)(FIELD_GET(SOCID_IMP_DEF_SOC_ID_MASK, (x)))
> +
> +static int soc_id_version;
> +static struct soc_device *soc_dev;
> +static struct soc_device_attribute *soc_dev_attr;
> +
> +static int smccc_map_error_codes(unsigned long a0)
> +{
> + if (a0 == SMCCC_RET_INVALID_PARAMETER)
> + return -EINVAL;
> + if (a0 == SMCCC_RET_NOT_SUPPORTED)
> + return -EOPNOTSUPP;
> + return 0;
It seems odd to special case just those errors. While they are the only
errors we expect, any result with the high bit set is an error (arguably
a bug in the firmware) so should really cause an error return.
> +}
> +
> +static int smccc_soc_id_support_check(void)
> +{
> + struct arm_smccc_res res;
> +
> + if (arm_smccc_1_1_get_conduit() == SMCCC_CONDUIT_NONE) {
> + pr_err("%s: invalid SMCCC conduit\n", __func__);
> + return -EOPNOTSUPP;
> + }
> +
> + arm_smccc_1_1_invoke(ARM_SMCCC_ARCH_FEATURES_FUNC_ID,
> + ARM_SMCCC_ARCH_SOC_ID, &res);
> +
> + return smccc_map_error_codes(res.a0);
> +}
> +
> +static ssize_t
> +jep106_cont_bank_code_show(struct device *dev, struct device_attribute *attr,
> + char *buf)
> +{
> + return sprintf(buf, "%02x\n", JEP106_BANK_IDX(soc_id_version) + 1);
> +}
> +
> +static DEVICE_ATTR_RO(jep106_cont_bank_code);
> +
> +static ssize_t
> +jep106_identification_code_show(struct device *dev,
> + struct device_attribute *attr, char *buf)
> +{
> + return sprintf(buf, "%02x\n", JEP106_ID_CODE(soc_id_version) & 0x7F);
It seems odd to have the mask defined to include a bit that is then
always masked off. From the spec I presume this is a parity bit, but it
would be good to have a comment explaining this.
> +}
> +
> +static DEVICE_ATTR_RO(jep106_identification_code);
> +
> +static struct attribute *jep106_id_attrs[] = {
> + &dev_attr_jep106_cont_bank_code.attr,
> + &dev_attr_jep106_identification_code.attr,
> + NULL
> +};
> +
> +ATTRIBUTE_GROUPS(jep106_id);
> +
> +static int __init smccc_soc_init(void)
> +{
> + struct device *dev;
> + int ret, soc_id_rev;
> + struct arm_smccc_res res;
> + static char soc_id_str[8], soc_id_rev_str[12];
> +
> + if (arm_smccc_get_version() < ARM_SMCCC_VERSION_1_2)
> + return 0;
NIT: Do we actually need to check the version here - or would probing
ARM_SMCCC_ARCH_FEATURES_FUNC_ID as is done below sufficient? I'm not
aware of this relying on any new semantics that v1.2 added.
> +
> + ret = smccc_soc_id_support_check();
> + if (ret)
> + return ret;
This seems odd - if the version is <v1.2 then we return 0. But if it's
>=1.2 but doesn't support SOC_ID then it's an error return?
> +
> + arm_smccc_1_1_invoke(ARM_SMCCC_ARCH_SOC_ID, 0, &res);
> +
> + ret = smccc_map_error_codes(res.a0);
> + if (ret)
> + return ret;
> +
> + soc_id_version = res.a0;
> +
> + arm_smccc_1_1_invoke(ARM_SMCCC_ARCH_SOC_ID, 1, &res);
> +
> + ret = smccc_map_error_codes(res.a0);
> + if (ret)
> + return ret;
> +
> + soc_id_rev = res.a0;
> +
> + soc_dev_attr = kzalloc(sizeof(*soc_dev_attr), GFP_KERNEL);
> + if (!soc_dev_attr)
> + return -ENOMEM;
> +
> + sprintf(soc_id_str, "0x%04x", IMP_DEF_SOC_ID(soc_id_version));
> + sprintf(soc_id_rev_str, "0x%08x", soc_id_rev);
> +
> + soc_dev_attr->soc_id = soc_id_str;
> + soc_dev_attr->revision = soc_id_rev_str;
> +
> + soc_dev = soc_device_register(soc_dev_attr);
> + if (IS_ERR(soc_dev)) {
> + ret = PTR_ERR(soc_dev);
> + goto free_soc;
> + }
> +
> + dev = soc_device_to_device(soc_dev);
> +
> + ret = devm_device_add_groups(dev, jep106_id_groups);
> + if (ret) {
> + dev_err(dev, "sysfs create failed: %d\n", ret);
> + goto unregister_soc;
> + }
> +
> + pr_info("SMCCC SoC ID: %s Revision %s\n", soc_dev_attr->soc_id,
> + soc_dev_attr->revision);
> +
> + return 0;
> +
> +unregister_soc:
> + soc_device_unregister(soc_dev);
> +free_soc:
> + kfree(soc_dev_attr);
> + return ret;
> +}
> +module_init(smccc_soc_init);
> +
> +static void __exit smccc_soc_exit(void)
> +{
> + if (soc_dev)
> + soc_device_unregister(soc_dev);
> + kfree(soc_dev_attr);
> +}
> +module_exit(smccc_soc_exit);
> diff --git a/include/linux/arm-smccc.h b/include/linux/arm-smccc.h
> index d6b0f4acc707..04414fc2000f 100644
> --- a/include/linux/arm-smccc.h
> +++ b/include/linux/arm-smccc.h
> @@ -68,6 +68,11 @@
> ARM_SMCCC_SMC_32, \
> 0, 1)
>
> +#define ARM_SMCCC_ARCH_SOC_ID \
> + ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL, \
> + ARM_SMCCC_SMC_32, \
> + 0, 2)
> +
> #define ARM_SMCCC_ARCH_WORKAROUND_1 \
> ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL, \
> ARM_SMCCC_SMC_32, \
>
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