Re: [PATCH V3 11/20] RISC-V: ACPI: Cache and retrieve the RINTC structure

[Andrew Jones <ajones@ventanamicro.com>]

On Fri, Mar 03, 2023 at 07:06:38PM +0530, Sunil V L wrote:
> RINTC structures in the MADT provide mapping between the hartid
> and the CPU. This is required many times even at run time like
> cpuinfo. So, instead of parsing the ACPI table every time, cache
> the RINTC structures and provide a function to get the correct
> RINTC structure for a given cpu.
> 
> Signed-off-by: Sunil V L <sunilvl@ventanamicro.com>
> Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---
>  arch/riscv/include/asm/acpi.h |  9 ++++++
>  arch/riscv/kernel/acpi.c      | 56 +++++++++++++++++++++++++++++++++++
>  2 files changed, 65 insertions(+)
> 
> diff --git a/arch/riscv/include/asm/acpi.h b/arch/riscv/include/asm/acpi.h
> index 111a8ed10af1..8be16c1ef7da 100644
> --- a/arch/riscv/include/asm/acpi.h
> +++ b/arch/riscv/include/asm/acpi.h
> @@ -61,6 +61,10 @@ static inline void arch_fix_phys_package_id(int num, u32 slot) { }
>  
>  int acpi_get_riscv_isa(struct acpi_table_header *table,
>  		       unsigned int cpu, const char **isa);
> +
> +struct acpi_madt_rintc *acpi_cpu_get_madt_rintc(int cpu);
> +
> +u32 get_acpi_id_for_cpu(int cpu);
>  #else
>  static inline int acpi_get_riscv_isa(struct acpi_table_header *table,
>  				     unsigned int cpu, const char **isa)
> @@ -68,6 +72,11 @@ static inline int acpi_get_riscv_isa(struct acpi_table_header *table,
>  	return -EINVAL;
>  }
>  
> +static inline u32 get_acpi_id_for_cpu(int cpu)
> +{
> +	return -1;
> +}

Why do we need this stub? I wouldn't expect non-ACPI code to need an ACPI
ID.

> +
>  #endif /* CONFIG_ACPI */
>  
>  #endif /*_ASM_ACPI_H*/
> diff --git a/arch/riscv/kernel/acpi.c b/arch/riscv/kernel/acpi.c
> index 81d448c41714..8b3d68d8225f 100644
> --- a/arch/riscv/kernel/acpi.c
> +++ b/arch/riscv/kernel/acpi.c
> @@ -24,6 +24,62 @@ EXPORT_SYMBOL(acpi_disabled);
>  int acpi_pci_disabled = 1;	/* skip ACPI PCI scan and IRQ initialization */
>  EXPORT_SYMBOL(acpi_pci_disabled);
>  
> +static struct acpi_madt_rintc cpu_madt_rintc[NR_CPUS];
> +
> +static int acpi_parse_madt_rintc(union acpi_subtable_headers *header, const unsigned long end)
> +{
> +	struct acpi_madt_rintc *rintc = (struct acpi_madt_rintc *)header;
> +	int cpuid;
> +
> +	if (!(rintc->flags & ACPI_MADT_ENABLED))
> +		return 0;

Why not cache the data even when its disabled? We also cache the flags so
we can always check later too.

> +
> +	cpuid = riscv_hartid_to_cpuid(rintc->hart_id);
> +	if (cpuid >= 0 && cpuid < NR_CPUS)

What does it mean for the above check to fail? Bad ACPI tables?

> +		cpu_madt_rintc[cpuid] = *rintc;
> +
> +	return 0;
> +}
> +
> +static int acpi_init_rintc_array(void)
> +{
> +	if (acpi_table_parse_madt(ACPI_MADT_TYPE_RINTC, acpi_parse_madt_rintc, 0) > 0)
> +		return 0;
> +
> +	return -ENODEV;
> +}
> +
> +/*
> + * Instead of parsing (and freeing) the ACPI table, cache
> + * the RINTC structures since they are frequently used
> + * like in  cpuinfo.
> + */
> +struct acpi_madt_rintc *acpi_cpu_get_madt_rintc(int cpu)
> +{
> +	static bool rintc_init_done;
> +
> +	if (!rintc_init_done) {
> +		if (acpi_init_rintc_array()) {
> +			pr_err("No valid RINTC entries exist\n");
> +			return NULL;
> +		}
> +
> +		rintc_init_done = true;
> +	}
> +
> +	return &cpu_madt_rintc[cpu];
> +}
> +
> +u32 get_acpi_id_for_cpu(int cpu)
> +{
> +	struct acpi_madt_rintc *rintc = acpi_cpu_get_madt_rintc(cpu);
> +
> +	if (!rintc)
> +		return -1;

Is -1 defined as an invalid ACPI ID? I'm wondering if we shouldn't just
BUG in acpi_init_rintc_array() if we fail to initialize and then we can
unconditionally return rintc->uid here.

> +
> +	return rintc->uid;
> +}
> +
>  /*
>   * __acpi_map_table() will be called before paging_init(), so early_ioremap()
>   * or early_memremap() should be called here to for ACPI table mapping.
> -- 
> 2.34.1
>

Thanks,
drew