On Mon, Aug 15, 2022 at 04:56:58PM +0000, Jiaxun Yang wrote:
> Some application would like to know precise model and rev of processor
> to do errata workaround or optimization.
>
> Expose them in sysfs as:
> /sys/devices/system/cpu/cpuX/regs/identification/prid
> /sys/devices/system/cpu/cpuX/regs/identification/globalnumber
>
> Reusing AArch64 CPU registers directory.
>
> Signed-off-by: Jiaxun Yang <jiaxun.yang@xxxxxxxxxxx>
> ---
> v2: Drop static qualifier for kobj (gregkh)
> v3: Use kzalloc to allocate struct cpuregs.
> note: When Greg mentioned about static I was thinking about
> static qualifier of percpu variable. After reading documents
> again it turns out kobjs should be allocated at runtime. Arm64's
> cpuinfo kobj is also on a percpu variable... I guess that was a
> intentional use?
> ---
> .../ABI/testing/sysfs-devices-system-cpu | 11 ++
> arch/mips/kernel/topology.c | 103 ++++++++++++++++++
> 2 files changed, 114 insertions(+)
>
> diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
> index 5bf61881f012..adf855e7bb9b 100644
> --- a/Documentation/ABI/testing/sysfs-devices-system-cpu
> +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
> @@ -512,6 +512,17 @@ Description: information about CPUs heterogeneity.
>
> cpu_capacity: capacity of cpuX.
>
> +What: /sys/devices/system/cpu/cpuX/regs/
> + /sys/devices/system/cpu/cpuX/regs/identification/
> + /sys/devices/system/cpu/cpuX/regs/identification/prid
> + /sys/devices/system/cpu/cpuX/regs/identification/globalnumber
> +Date: Augest 2022
> +Contact: Linux MIPS Kernel Mailing list <linux-mips@xxxxxxxxxxxxxxx>
> +Description: MIPS CPU registers
> +
> + 'identification' directory exposes the Processor ID and Global Number
> + registers for identifying model and revision of the CPU.
> +
> What: /sys/devices/system/cpu/vulnerabilities
> /sys/devices/system/cpu/vulnerabilities/meltdown
> /sys/devices/system/cpu/vulnerabilities/spectre_v1
> diff --git a/arch/mips/kernel/topology.c b/arch/mips/kernel/topology.c
> index 9429d85a4703..bbb7d4b51ffe 100644
> --- a/arch/mips/kernel/topology.c
> +++ b/arch/mips/kernel/topology.c
> @@ -5,6 +5,8 @@
> #include <linux/node.h>
> #include <linux/nodemask.h>
> #include <linux/percpu.h>
> +#include <linux/seq_file.h>
> +#include <linux/smp.h>
>
> static DEFINE_PER_CPU(struct cpu, cpu_devices);
>
> @@ -26,3 +28,104 @@ static int __init topology_init(void)
> }
>
> subsys_initcall(topology_init);
> +
> +static struct kobj_type cpuregs_kobj_type = {
> + .sysfs_ops = &kobj_sysfs_ops,
> +};
> +
> +struct cpureg {
> + struct kobject kobj;
> + struct cpuinfo_mips *info;
> +};
> +static DEFINE_PER_CPU(struct cpureg *, cpuregs);
> +
> +#define kobj_to_cpureg(kobj) container_of(kobj, struct cpureg, kobj)
> +#define CPUREGS_ATTR_RO(_name, _field) \
> + static ssize_t _name##_show(struct kobject *kobj, \
> + struct kobj_attribute *attr, char *buf) \
> + { \
> + struct cpuinfo_mips *info = kobj_to_cpureg(kobj)->info; \
> + \
> + return sprintf(buf, "0x%08x\n", info->_field); \
> + } \
> + static struct kobj_attribute cpuregs_attr_##_name = __ATTR_RO(_name)
> +
> +CPUREGS_ATTR_RO(prid, processor_id);
> +CPUREGS_ATTR_RO(globalnumber, globalnumber);
> +
> +static struct attribute *cpuregs_id_attrs[] = {
> + &cpuregs_attr_prid.attr,
> + &cpuregs_attr_globalnumber.attr,
> + NULL
> +};
> +
> +static const struct attribute_group cpuregs_attr_group = {
> + .attrs = cpuregs_id_attrs,
> + .name = "identification"
> +};
> +
> +static int cpuregs_cpu_online(unsigned int cpu)
> +{
> + int rc;
> + struct device *dev;
> + struct cpureg *reg;
> +
> + dev = get_cpu_device(cpu);
> + if (!dev) {
> + rc = -ENODEV;
> + goto out;
> + }
> + reg = kzalloc(sizeof(struct cpureg), GFP_KERNEL);
> + if (!reg) {
> + rc = -ENOMEM;
> + goto out;
> + }
> + rc = kobject_init_and_add(®->kobj, &cpuregs_kobj_type,
> + &dev->kobj, "regs");
> + if (rc)
> + goto out_kfree;
No, please read the documentation for kobject_init_and_add() for what to
properly do in a failure of this function.
thanks,
greg k-h
