Re: [PATCH] MIPS: Expose prid and globalnumber to sysfs

[Greg KH]

On Tue, Aug 09, 2022 at 11:34:44AM +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>
> ---
>  .../ABI/testing/sysfs-devices-system-cpu      | 11 +++
>  arch/mips/kernel/topology.c                   | 96 +++++++++++++++++++
>  2 files changed, 107 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..90b5136afb63 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 +28,97 @@ 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);

static kobjects are nothing you should ever create willingly.  That's a
dynamic reference counted structure being declared on the "stack"?

Please no.

thanks,

greg k-h