linux-kernel - Re: [PATCH v1 2/5] ACPI: bus: Set CPPC _OSC bits for all and when CPPC

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Message-ID: <20220511142220.sjfhikuf6fydnrkb@bogus>
Date:   Wed, 11 May 2022 15:22:20 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Pierre Gondois <pierre.gondois@....com>
Cc:     linux-kernel@...r.kernel.org, Ionela.Voinescu@....com,
        Sudeep Holla <sudeep.holla@....com>, Dietmar.Eggemann@....com,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Robert Moore <robert.moore@...el.com>,
        linux-acpi@...r.kernel.org, linux-pm@...r.kernel.org,
        devel@...ica.org
Subject: Re: [PATCH v1 2/5] ACPI: bus: Set CPPC _OSC bits for all and when
 CPPC_LIB is supported

On Wed, May 11, 2022 at 03:45:56PM +0200, Pierre Gondois wrote:
> The _OSC method allows the OS and firmware to communicate about
> supported features/capabitlities. It also allows the OS to take
> control of some features.
> 
> In ACPI 6.4, s6.2.11.2 Platform-Wide OSPM Capabilities, the CPPC
> (resp. v2) bit should be set by the OS if it 'supports controlling
> processor performance via the interfaces described in the _CPC
> object'.
> 
> The OS supports CPPC and parses the _CPC object only if
> CONFIG_ACPI_CPPC_LIB is set. Replace the x86 specific
> boot_cpu_has(X86_FEATURE_HWP) dynamic check with an arch
> generic CONFIG_ACPI_CPPC_LIB build-time check.
> 
> Note:
> CONFIG_X86_INTEL_PSTATE selects CONFIG_ACPI_CPPC_LIB.

While this is work as per the spec, by not sure what kind of ACPI firmware are
in the wild. So be prepared to relax/constrain to original feature check
for x86, unfortunate but may be needed.

Anyways,

Reviewed-by: Sudeep Holla <sudeep.holla@....com>

-- 
Regards,
Sudeep