linux-kernel - Re: [PATCH v2] RISC-V: Add mvendorid, marchid, and mimpid to /proc/cpuinfo output

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Date:   Wed, 27 Jul 2022 09:55:29 +0100
From:   Ben Dooks <ben.dooks@...ethink.co.uk>
To:     Anup Patel <apatel@...tanamicro.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>
Cc:     Arnd Bergmann <arnd@...db.de>, Anup Patel <anup@...infault.org>,
        linux-kernel@...r.kernel.org,
        Heinrich Schuchardt <heinrich.schuchardt@...onical.com>,
        Atish Patra <atishp@...shpatra.org>,
        linux-riscv@...ts.infradead.org, Nikita Shubin <n.shubin@...ro.com>
Subject: Re: [PATCH v2] RISC-V: Add mvendorid, marchid, and mimpid to
 /proc/cpuinfo output

On 27/07/2022 05:38, Anup Patel wrote:
> Identifying the underlying RISC-V implementation can be important
> for some of the user space applications. For example, the perf tool
> uses arch specific CPU implementation id (i.e. CPUID) to select a
> JSON file describing custom perf events on a CPU.
> 
> Currently, there is no way to identify RISC-V implementation so we
> add mvendorid, marchid, and mimpid to /proc/cpuinfo output.
> 
> Signed-off-by: Anup Patel <apatel@...tanamicro.com>
> Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@...onical.com>
> Tested-by: Nikita Shubin <n.shubin@...ro.com>
> ---
> Changes since v1:
>   - Use IS_ENABLED() to check CONFIG defines
>   - Added RB and TB tags in commit description
> ---
>   arch/riscv/kernel/cpu.c | 51 +++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 51 insertions(+)
> 
> diff --git a/arch/riscv/kernel/cpu.c b/arch/riscv/kernel/cpu.c
> index fba9e9f46a8c..04bcc91c91ea 100644
> --- a/arch/riscv/kernel/cpu.c
> +++ b/arch/riscv/kernel/cpu.c
> @@ -3,10 +3,13 @@
>    * Copyright (C) 2012 Regents of the University of California
>    */
>   
> +#include <linux/cpu.h>
>   #include <linux/init.h>
>   #include <linux/seq_file.h>
>   #include <linux/of.h>
> +#include <asm/csr.h>
>   #include <asm/hwcap.h>
> +#include <asm/sbi.h>
>   #include <asm/smp.h>
>   #include <asm/pgtable.h>
>   
> @@ -64,6 +67,50 @@ int riscv_of_parent_hartid(struct device_node *node)
>   }
>   
>   #ifdef CONFIG_PROC_FS
> +
> +struct riscv_cpuinfo {
> +	unsigned long mvendorid;
> +	unsigned long marchid;
> +	unsigned long mimpid;
> +};
> +static DEFINE_PER_CPU(struct riscv_cpuinfo, riscv_cpuinfo);
> +
> +static int riscv_cpuinfo_starting(unsigned int cpu)
> +{
> +	struct riscv_cpuinfo *ci = this_cpu_ptr(&riscv_cpuinfo);
> +
> +#if IS_ENABLED(CONFIG_RISCV_SBI)
> +	ci->mvendorid = sbi_spec_is_0_1() ? 0 : sbi_get_mvendorid();
> +	ci->marchid = sbi_spec_is_0_1() ? 0 : sbi_get_marchid();
> +	ci->mimpid = sbi_spec_is_0_1() ? 0 : sbi_get_mimpid();

how about:

	if (IS_ENABLED(CONFIG_RISCV_SBI)) {
		...	
	} ... {

or maybe even:


	if (IS_ENABLED(CONFIG_RISCV_SBI)) {
		if (sbi_spec_is_0_1()) {
			...
		}	
	} ... {

would mean better compile coverage (at the slight exepnese of
having "false" sbi_spec_is_0_1() implemenation

> +#elif IS_ENABLED(CONFIG_RISCV_M_MODE)
> +	ci->mvendorid = csr_read(CSR_MVENDORID);
> +	ci->marchid = csr_read(CSR_MARCHID);
> +	ci->mimpid = csr_read(CSR_MIMPID);
> +#else
> +	ci->mvendorid = 0;
> +	ci->marchid = 0;
> +	ci->mimpid = 0;
> +#endif

Would it be easier to zero out all the fields first and then fill them
in if supported?

> +
> +	return 0;
> +}
> +
> +static int __init riscv_cpuinfo_init(void)
> +{
> +	int ret;
> +
> +	ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "riscv/cpuinfo:starting",
> +				riscv_cpuinfo_starting, NULL);
> +	if (ret < 0) {
> +		pr_err("cpuinfo: failed to register hotplug callbacks.\n");
> +		return ret;
> +	}
> +
> +	return 0;
> +}
> +device_initcall(riscv_cpuinfo_init);
> +
>   #define __RISCV_ISA_EXT_DATA(UPROP, EXTID) \
>   	{							\
>   		.uprop = #UPROP,				\
> @@ -178,6 +225,7 @@ static int c_show(struct seq_file *m, void *v)
>   {
>   	unsigned long cpu_id = (unsigned long)v - 1;
>   	struct device_node *node = of_get_cpu_node(cpu_id, NULL);
> +	struct riscv_cpuinfo *ci = per_cpu_ptr(&riscv_cpuinfo, cpu_id);
>   	const char *compat, *isa;
>   
>   	seq_printf(m, "processor\t: %lu\n", cpu_id);
> @@ -188,6 +236,9 @@ static int c_show(struct seq_file *m, void *v)
>   	if (!of_property_read_string(node, "compatible", &compat)
>   	    && strcmp(compat, "riscv"))
>   		seq_printf(m, "uarch\t\t: %s\n", compat);
> +	seq_printf(m, "mvendorid\t: 0x%lx\n", ci->mvendorid);
> +	seq_printf(m, "marchid\t\t: 0x%lx\n", ci->marchid);
> +	seq_printf(m, "mimpid\t\t: 0x%lx\n", ci->mimpid);
>   	seq_puts(m, "\n");
>   	of_node_put(node);
>   


-- 
Ben Dooks				http://www.codethink.co.uk/
Senior Engineer				Codethink - Providing Genius

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