Re: [PATCH v2] cpuidle, ACPI: Evaluate LPI arch_flags for broadcast timer

[Rafael J. Wysocki]

On Mon, Aug 7, 2023 at 5:48 PM Oza Pawandeep <quic_poza@xxxxxxxxxxx> wrote:
>
> Arm® Functional Fixed Hardware Specification defines LPI states, which provide
> an architectural context loss flags field that can be used to describe the
> context that might be lost when an LPI state is entered.
>
> - Core context Lost
>         - General purpose registers.
>         - Floating point and SIMD registers.
>         - System registers, include the System register based
>         - generic timer for the core.
>         - Debug register in the core power domain.
>         - PMU registers in the core power domain.
>         - Trace register in the core power domain.
> - Trace context loss
> - GICR
> - GICD
>
> Qualcomm's custom CPUs preserves the architectural state,
> including keeping the power domain for local timers active.
> when core is power gated, the local timers are sufficient to
> wake the core up without needing broadcast timer.
>
> The patch fixes the evaluation of cpuidle arch_flags, and moves only to
> broadcast timer if core context lost is defined in ACPI LPI.
>
> Signed-off-by: Oza Pawandeep <quic_poza@xxxxxxxxxxx>
>
> diff --git a/arch/arm64/include/asm/acpi.h b/arch/arm64/include/asm/acpi.h
> index bd68e1b7f29f..5493b044864f 100644
> --- a/arch/arm64/include/asm/acpi.h
> +++ b/arch/arm64/include/asm/acpi.h
> @@ -9,6 +9,7 @@
>  #ifndef _ASM_ACPI_H
>  #define _ASM_ACPI_H
>
> +#include <linux/cpuidle.h>
>  #include <linux/efi.h>
>  #include <linux/memblock.h>
>  #include <linux/psci.h>
> @@ -42,6 +43,27 @@
>  #define ACPI_MADT_GICC_SPE  (offsetof(struct acpi_madt_generic_interrupt, \
>         spe_interrupt) + sizeof(u16))
>
> +/*
> + * Arm® Functional Fixed Hardware Specification Version 1.2.
> + * Table 2: Arm Architecture context loss flags
> + */
> +#define CPUIDLE_CORE_CTXT              BIT(0) /* Core context Lost */
> +
> +#ifndef arch_update_idle_state_flags
> +static __always_inline void arch_update_idle_state_flags(u32 arch_flags,
> +                                                       unsigned int *sflags)
> +{
> +  if (arch_flags & CPUIDLE_CORE_CTXT) {
> +       *sflags |= CPUIDLE_FLAG_TIMER_STOP;
> +  }
> +}
> +#define arch_update_idle_state_flags arch_update_idle_state_flags
> +#endif
> +
> +#define CPUIDLE_TRACE_CTXT             BIT(1) /* Trace context loss */
> +#define CPUIDLE_GICR_CTXT              BIT(2) /* GICR */
> +#define CPUIDLE_GICD_CTXT              BIT(3) /* GICD */
> +
>  /* Basic configuration for ACPI */
>  #ifdef CONFIG_ACPI
>  pgprot_t __acpi_get_mem_attribute(phys_addr_t addr);
> diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
> index 9718d07cc2a2..420baec3465c 100644
> --- a/drivers/acpi/processor_idle.c
> +++ b/drivers/acpi/processor_idle.c
> @@ -1221,8 +1221,7 @@ static int acpi_processor_setup_lpi_states(struct acpi_processor *pr)
>                 strscpy(state->desc, lpi->desc, CPUIDLE_DESC_LEN);
>                 state->exit_latency = lpi->wake_latency;
>                 state->target_residency = lpi->min_residency;
> -               if (lpi->arch_flags)
> -                       state->flags |= CPUIDLE_FLAG_TIMER_STOP;
> +               arch_update_idle_state_flags(lpi->arch_flags, &state->flags);
>                 if (i != 0 && lpi->entry_method == ACPI_CSTATE_FFH)
>                         state->flags |= CPUIDLE_FLAG_RCU_IDLE;
>                 state->enter = acpi_idle_lpi_enter;
> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
> index d584f94409e1..60f17c99465b 100644
> --- a/include/linux/acpi.h
> +++ b/include/linux/acpi.h
> @@ -1471,6 +1471,15 @@ static inline int lpit_read_residency_count_address(u64 *address)
>  }
>  #endif
>
> +#ifndef arch_update_idle_state_flags
> +static __always_inline void arch_update_idle_state_flags(u32 arch_flags,
> +                                                       unsigned int *sflags)
> +{
> +
> +}
> +#define arch_update_idle_state_flags arch_update_idle_state_flags
> +#endif
> +
>  #ifdef CONFIG_ACPI_PPTT
>  int acpi_pptt_cpu_is_thread(unsigned int cpu);
>  int find_acpi_cpu_topology(unsigned int cpu, int level);
> --

If I'm to apply this, an ACK from the ARM people is requisite.

Thanks!