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From:   "Pawandeep Oza (QUIC)" <quic_poza@quicinc.com>
To:     'Sudeep Holla' <sudeep.holla@arm.com>,
        "Pawandeep Oza (QUIC)" <quic_poza@quicinc.com>
CC:     Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        "Rafael J . Wysocki" <rafael@kernel.org>,
        Len Brown <lenb@kernel.org>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-acpi@vger.kernel.org" <linux-acpi@vger.kernel.org>,
        Jamie Iles <jiles@qti.qualcomm.com>
Subject: RE: [PATCH] cpuidle, ACPI: Evaluate LPI arch_flags for broadcast
 timer
Thread-Topic: [PATCH] cpuidle, ACPI: Evaluate LPI arch_flags for broadcast
 timer
Thread-Index: AQHZtOXPWJW8A9EhYUWJUYorSZkKy6+/jquAgA6BpPE=
Date:   Thu, 27 Jul 2023 19:03:42 +0000
Message-ID: <CH0PR02MB8073B417648AB9DE5D8E25B2F601A@CH0PR02MB8073.namprd02.prod.outlook.com>
References: <20230712172458.2507434-1-quic_poza@quicinc.com>
 <20230718133201.qsulwupte6l6bmdm@bogus>
In-Reply-To: <20230718133201.qsulwupte6l6bmdm@bogus>
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Hi Sudeep,

Please find my comments inline.

Regards,
Oza.

-----Original Message-----
From: Sudeep Holla <sudeep.holla@arm.com>=20
Sent: Tuesday, July 18, 2023 6:32 AM
To: Pawandeep Oza (QUIC) <quic_poza@quicinc.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>; Will Deacon <will@kernel.org=
>; Sudeep Holla <sudeep.holla@arm.com>; Rafael J . Wysocki <rafael@kernel.o=
rg>; Len Brown <lenb@kernel.org>; linux-arm-kernel@lists.infradead.org; lin=
ux-kernel@vger.kernel.org; linux-acpi@vger.kernel.org; Jamie Iles <jiles@qt=
i.qualcomm.com>
Subject: Re: [PATCH] cpuidle, ACPI: Evaluate LPI arch_flags for broadcast t=
imer

On Wed, Jul 12, 2023 at 10:24:58AM -0700, Oza Pawandeep wrote:
> Arm(r) Functional Fixed Hardware Specification defines LPI states, which=
=20
> provides an architectural context loss flags field that can be used to=20
> describe the context that might be lost when an LPI state is entered.
>=20
> - 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
>=20
> Qualcomm's custom CPUs preserves the architectural state, including=20
> keeping the power domain for local timers active.
> when core is power gated, the local timers are sufficient to wake the=20
> core up without needing broadcast timer.
>=20
> The patch fixes the evaluation of cpuidle arch_flags, and moves only=20
> to broadcast timer if core context lost is defined in ACPI LPI.
>=20
> Signed-off-by: Oza Pawandeep <quic_poza@quicinc.com>
>=20
> diff --git a/arch/arm64/include/asm/acpi.h=20
> b/arch/arm64/include/asm/acpi.h index bd68e1b7f29f..9c335968316c=20
> 100644
> --- a/arch/arm64/include/asm/acpi.h
> +++ b/arch/arm64/include/asm/acpi.h
> @@ -42,6 +42,24 @@
>  #define ACPI_MADT_GICC_SPE  (offsetof(struct acpi_madt_generic_interrupt=
, \
>  	spe_interrupt) + sizeof(u16))
> =20
> +/*
> + * 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 */
> +
> +#ifndef arch_acpi_lpi_timer_stopped
> +static __always_inline bool arch_acpi_lpi_timer_stopped(u32=20
> +arch_flags)

As mentioned by you above, the core context is not just timer context, so c=
alling this function so is misleading.

 Oza: Will take care of you last 2 comments, probably this should be taken =
care as well with that.

> +{
> +  return arch_flags & CPUIDLE_CORE_CTXT; } #define=20
> +arch_acpi_lpi_timer_stopped arch_acpi_lpi_timer_stopped #endif
> +
> +#define CPUIDLE_TRACE_CTXT		BIT(1) /* Trace context loss */
> +#define CPUIDLE_GICR_CTXT		BIT(2) /* GICR */
> +#define CPUIDLE_GICD_CTXT		BIT(3) /* GICD */
> +

Do we really need to define these unused bitfields ? DO you have plans to u=
se them ?

Oza: this is basically defined in ARM FFH - I think no harm is having them =
here for sake of completeness.

>  /* Basic configuration for ACPI */
>  #ifdef	CONFIG_ACPI
>  pgprot_t __acpi_get_mem_attribute(phys_addr_t addr); diff --git=20
> a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c index=20
> 9718d07cc2a2..8ea1f2b3bf96 100644
> --- a/drivers/acpi/processor_idle.c
> +++ b/drivers/acpi/processor_idle.c
> @@ -1221,7 +1221,7 @@ static int acpi_processor_setup_lpi_states(struct a=
cpi_processor *pr)
>  		strscpy(state->desc, lpi->desc, CPUIDLE_DESC_LEN);
>  		state->exit_latency =3D lpi->wake_latency;
>  		state->target_residency =3D lpi->min_residency;
> -		if (lpi->arch_flags)
> +		if (arch_acpi_lpi_timer_stopped(lpi->arch_flags))

While setting CPUIDLE_FLAG_TIMER_STOP if any flags set is already questiona=
ble, checking for arch specific flag in the generic code is even more quest=
ionable now. I wonder if it makes more sense to have a arch specific helper=
 to update the state->flags based on how arch specific interpretation of lp=
i->arch_flags ?

>  			state->flags |=3D CPUIDLE_FLAG_TIMER_STOP;
>  		if (i !=3D 0 && lpi->entry_method =3D=3D ACPI_CSTATE_FFH)
>  			state->flags |=3D CPUIDLE_FLAG_RCU_IDLE; diff --git=20
> a/include/linux/acpi.h b/include/linux/acpi.h index=20
> d584f94409e1..b24f1cd1cebb 100644
> --- a/include/linux/acpi.h
> +++ b/include/linux/acpi.h
> @@ -1471,6 +1471,14 @@ static inline int=20
> lpit_read_residency_count_address(u64 *address)  }  #endif
> =20
> +#ifndef arch_acpi_lpi_timer_stopped
> +static __always_inline bool arch_acpi_lpi_timer_stopped(u32=20
> +arch_flags) {
> +  return (arch_flags !=3D 0);
> +}
> +#define arch_acpi_lpi_timer_stopped arch_acpi_lpi_timer_stopped=20
> +#endif
> +

This looks ugly and main reason for my above comment. I am thinking of arch=
_update_idle_state_flags(lpi->arch_flags, &state->flags) and make it do not=
hing on non arm platforms. I don't think we will be breaking anything(i.e. =
no need to check arch_flags !=3D 0. It is incorrect strictly speaking but t=
here are no non-arm users ATM, but that doesn't mean we can trickle the arc=
h specific LPI FFH details into the generic code.

Oza: Let me work on above 2 comments and post the new patch.

--
Regards,
Sudeep