linux-kernel - Re: [PATCH v3] cpuidle, ACPI: Evaluate LPI arch

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Message-ID: <a4811a5e1df589573a27771749a68d34@kernel.org>
Date:   Wed, 30 Aug 2023 15:07:35 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Oza Pawandeep <quic_poza@...cinc.com>
Cc:     sudeep.holla@....com, catalin.marinas@....com, will@...nel.org,
        rafael@...nel.org, lenb@...nel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-acpi@...r.kernel.org
Subject: Re: [PATCH v3] cpuidle, ACPI: Evaluate LPI arch_flags for broadcast
 timer

On 2023-08-29 21:11, Oza Pawandeep 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.

Isn't that what should be exposed by GTDT when ACPI_GTDT_ALWAYS_ON
is set on the relevant interrupt and EL? The arch timer already
deals with that.

Why do we need anything else?

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...