Re: [PATCH 3/5] LoongArch: cpu-probe: Move IOCSR probing out of cpu_probe_common

[Huacai Chen]

Hi, Jiaxun,

On Sat, Sep 7, 2024 at 6:17 PM Jiaxun Yang <jiaxun.yang@xxxxxxxxxxx> wrote:
>
> IOCSR register definition appears to be a platform specific
> spec instead of architecture spec, even for Loongson CPUs
> there is no guarantee that IOCSR will always present.
>
> Thus it's dangerous to perform IOCSR probing without checking
> CPU type and instruction availability.
I don't think this is necessary. Loongson's Chip engineers confirm
that IOCSR is always present in Loongson processors. If other
LoongArch (not Loongson) processors have no IOCSR, they should
implement their own cpu_probe_abc() instead of cpu_probe_loongson().

Huacai

>
> Signed-off-by: Jiaxun Yang <jiaxun.yang@xxxxxxxxxxx>
> ---
>  arch/loongarch/kernel/cpu-probe.c | 63 ++++++++++++++++++++++++---------------
>  1 file changed, 39 insertions(+), 24 deletions(-)
>
> diff --git a/arch/loongarch/kernel/cpu-probe.c b/arch/loongarch/kernel/cpu-probe.c
> index 6a82ceb6e321..968b5a35a0d2 100644
> --- a/arch/loongarch/kernel/cpu-probe.c
> +++ b/arch/loongarch/kernel/cpu-probe.c
> @@ -173,22 +173,6 @@ static void cpu_probe_common(struct cpuinfo_loongarch *c)
>         if (config & CPUCFG6_PMP)
>                 c->options |= LOONGARCH_CPU_PMP;
>
> -       config = iocsr_read32(LOONGARCH_IOCSR_FEATURES);
> -       if (config & IOCSRF_CSRIPI)
> -               c->options |= LOONGARCH_CPU_CSRIPI;
> -       if (config & IOCSRF_EXTIOI)
> -               c->options |= LOONGARCH_CPU_EXTIOI;
> -       if (config & IOCSRF_FREQSCALE)
> -               c->options |= LOONGARCH_CPU_SCALEFREQ;
> -       if (config & IOCSRF_FLATMODE)
> -               c->options |= LOONGARCH_CPU_FLATMODE;
> -       if (config & IOCSRF_EIODECODE)
> -               c->options |= LOONGARCH_CPU_EIODECODE;
> -       if (config & IOCSRF_AVEC)
> -               c->options |= LOONGARCH_CPU_AVECINT;
> -       if (config & IOCSRF_VM)
> -               c->options |= LOONGARCH_CPU_HYPERVISOR;
> -
>         config = csr_read32(LOONGARCH_CSR_ASID);
>         config = (config & CSR_ASID_BIT) >> CSR_ASID_BIT_SHIFT;
>         asid_mask = GENMASK(config - 1, 0);
> @@ -231,16 +215,8 @@ static char cpu_full_name[MAX_NAME_LEN] = "        -        ";
>
>  static inline void cpu_probe_loongson(struct cpuinfo_loongarch *c, unsigned int cpu)
>  {
> -       uint64_t *vendor = (void *)(&cpu_full_name[VENDOR_OFFSET]);
> -       uint64_t *cpuname = (void *)(&cpu_full_name[CPUNAME_OFFSET]);
>         const char *core_name = "Unknown";
>
> -       if (!__cpu_full_name[cpu])
> -               __cpu_full_name[cpu] = cpu_full_name;
> -
> -       *vendor = iocsr_read64(LOONGARCH_IOCSR_VENDOR);
> -       *cpuname = iocsr_read64(LOONGARCH_IOCSR_CPUNAME);
> -
>         switch (c->processor_id & PRID_SERIES_MASK) {
>         case PRID_SERIES_LA132:
>                 c->cputype = CPU_LOONGSON32;
> @@ -283,6 +259,36 @@ static inline void cpu_probe_loongson(struct cpuinfo_loongarch *c, unsigned int
>         pr_info("%s Processor probed (%s Core)\n", __cpu_family[cpu], core_name);
>  }
>
> +static inline void iocsr_probe_loongson(struct cpuinfo_loongarch *c, unsigned int cpu)
> +{
> +       uint64_t *vendor = (void *)(&cpu_full_name[VENDOR_OFFSET]);
> +       uint64_t *cpuname = (void *)(&cpu_full_name[CPUNAME_OFFSET]);
> +       unsigned int config;
> +
> +       *vendor = iocsr_read64(LOONGARCH_IOCSR_VENDOR);
> +       *cpuname = iocsr_read64(LOONGARCH_IOCSR_CPUNAME);
> +
> +       if (!__cpu_full_name[cpu])
> +               __cpu_full_name[cpu] = cpu_full_name;
> +
> +       config = iocsr_read32(LOONGARCH_IOCSR_FEATURES);
> +       if (config & IOCSRF_CSRIPI)
> +               c->options |= LOONGARCH_CPU_CSRIPI;
> +       if (config & IOCSRF_EXTIOI)
> +               c->options |= LOONGARCH_CPU_EXTIOI;
> +       if (config & IOCSRF_FREQSCALE)
> +               c->options |= LOONGARCH_CPU_SCALEFREQ;
> +       if (config & IOCSRF_FLATMODE)
> +               c->options |= LOONGARCH_CPU_FLATMODE;
> +       if (config & IOCSRF_EIODECODE)
> +               c->options |= LOONGARCH_CPU_EIODECODE;
> +       if (config & IOCSRF_AVEC)
> +               c->options |= LOONGARCH_CPU_AVECINT;
> +       if (config & IOCSRF_VM)
> +               c->options |= LOONGARCH_CPU_HYPERVISOR;
> +
> +}
> +
>  #ifdef CONFIG_64BIT
>  /* For use by uaccess.h */
>  u64 __ua_limit;
> @@ -331,6 +337,15 @@ void cpu_probe(void)
>                 break;
>         }
>
> +       if (c->options & LOONGARCH_CPU_IOCSR) {
> +               switch (c->cputype) {
> +               case CPU_LOONGSON32:
> +               case CPU_LOONGSON64:
> +                       iocsr_probe_loongson(c, cpu);
> +                       break;
> +               }
> +       }
> +
>         BUG_ON(!__cpu_family[cpu]);
>         BUG_ON(c->cputype == CPU_UNKNOWN);
>
>
> --
> 2.46.0
>