-----Original Message-----
From: Will Deacon <will@xxxxxxxxxx>
Sent: Friday, September 29, 2023 8:05 AM
To: Pawandeep Oza (QUIC) <quic_poza@xxxxxxxxxxx>
Cc: sudeep.holla@xxxxxxx; catalin.marinas@xxxxxxx; rafael@xxxxxxxxxx; lenb@xxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; linux-acpi@xxxxxxxxxxxxxxx
Subject: Re: [PATCH v8] cpuidle, ACPI: Evaluate LPI arch_flags for broadcast timer
On Mon, Sep 18, 2023 at 10:21:40AM -0700, Oza Pawandeep wrote:
> Arm(r) 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.
>
> Fixes: a36a7fecfe607 ("Add support for Low Power Idle(LPI) states")
> Reviewed-by: Sudeep Holla <sudeep.holla@xxxxxxx>
> Acked-by: Rafael J. Wysocki <rafael@xxxxxxxxxx>
> Signed-off-by: Oza Pawandeep <quic_poza@xxxxxxxxxxx>
> ---
>
> Notes:
> Will/Catalin: Rafael has acked and he prefers to take it via arm64
> tree
>
> diff --git a/arch/arm64/include/asm/acpi.h
> b/arch/arm64/include/asm/acpi.h index 4d537d56eb84..269d21209723
> 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>
> @@ -44,6 +45,23 @@
>
> #define ACPI_MADT_GICC_TRBE (offsetof(struct acpi_madt_generic_interrupt, \
> trbe_interrupt) + sizeof(u16))
> +/*
> + * Arm(r) Functional Fixed Hardware Specification Version 1.2.
> + * Table 2: Arm Architecture context loss flags */
> +#define CPUIDLE_CORE_CTXT BIT(0) /* Core context Lost */
> +
> +static __always_inline void _arch_update_idle_state_flags(u32 arch_flags,
> + unsigned int *sflags)
Why can't this just be 'static inline'?
Oza: sure, will let compiler decide.
> +{
> + if (arch_flags & CPUIDLE_CORE_CTXT)
> + *sflags |= CPUIDLE_FLAG_TIMER_STOP; } #define
> +arch_update_idle_state_flags _arch_update_idle_state_flags
Usually, the function and the macro have the same name for this pattern, so I think it would be more consistent to drop the leading underscore from the C function name.
Oza: sure
> +
> +#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
> diff --git a/drivers/acpi/processor_idle.c
> b/drivers/acpi/processor_idle.c index dc615ef6550a..5c1d13eecdd1
> 100644
> --- a/drivers/acpi/processor_idle.c
> +++ b/drivers/acpi/processor_idle.c
> @@ -1217,8 +1217,7 @@ 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);
Hmm, I know Rafael has Acked this, but I think this is pretending to be more generic than it really is. While passing in a pointer to the flags field allows the arch code to set and clear arbitrary flags, we're calling this before we've set CPUIDLE_FLAG_RCU_IDLE, so that cannot be changed.
Why not just name it like it is and return the arch flags directly:
state->flags |= arch_get_idle_state_flags(lpi->arch_flags);
Oza:
?
> 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
> a73246c3c35e..07a825c76bab 100644
> --- a/include/linux/acpi.h
> +++ b/include/linux/acpi.h
> @@ -1480,6 +1480,12 @@ static inline int
> lpit_read_residency_count_address(u64 *address) } #endif
>
> +#ifdef CONFIG_ACPI_PROCESSOR_IDLE
> +#ifndef arch_update_idle_state_flags
> +#define arch_update_idle_state_flags(af, sf) do {} while (0)
I'd prefer defining this to point at an empty static inline function so that we get evaluation and type-checking of the arguments.
Oza: sure
> +#endif
> +#endif /* CONFIG_ACPI_PROCESSOR_IDLE */
Why do you need the outer CONFIG_ guards here?
Oza: this is because of non-ACPI kernel build issue for this config: https://download.01.org/0day-ci/archive/20230915/202309151138.69mFCPtW-lkp@xxxxxxxxx/config
Throwing following
"
All warnings (new ones prefixed by >>):
In file included from arch/arm64/kernel/setup.c:36:
>> arch/arm64/include/asm/acpi.h:60: warning:
>> "arch_update_idle_state_flags" redefined
60 | #define arch_update_idle_state_flags _arch_update_idle_state_flags
|
In file included from arch/arm64/kernel/setup.c:9:
include/linux/acpi.h:1484: note: this is the location of the previous definition
1484 | #define arch_update_idle_state_flags(af, sf) do {} while (0)
|
"
Will
