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Date:   Thu, 11 Aug 2022 19:21:57 -0700
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Subject: Re: [PATCH v2] MIPS: Expose prid and globalnumber to sysfs
Content-Language: en-US
To:     Jiaxun Yang <jiaxun.yang@flygoat.com>, linux-mips@vger.kernel.org
Cc:     linux-kernel@vger.kernel.org, tsbogend@alpha.franken.de,
        linux-api@vger.kernel.org
References: <20220811101236.1925-1-jiaxun.yang@flygoat.com>
From:   Florian Fainelli <f.fainelli@gmail.com>
In-Reply-To: <20220811101236.1925-1-jiaxun.yang@flygoat.com>
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On 8/11/2022 3:12 AM, 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@flygoat.com>
> ---
> v2: Drop static qualifier for kobj (gregkh)
> ---
>   .../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

typo: August

> +Contact:	Linux MIPS Kernel Mailing list <linux-mips@vger.kernel.org>
> +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..0e3730f3c00f 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;
> +};
> +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);	\

Would not you be able to simplify this greatly with just:

	struct cpuinfo_mips *info = current_cpu_data;

and not have to associate that with struct with the kobject?
-- 
Florian