From: Christian Loehle <christian.loehle@arm.com>
To: "Rafael J. Wysocki (Intel)" <rafael@kernel.org>
Cc: Viresh Kumar <viresh.kumar@linaro.org>,
linux-pm@vger.kernel.org, linux-acpi@vger.kernel.org,
linux-kernel@vger.kernel.org, Jie Zhan <zhanjie9@hisilicon.com>,
Lifeng Zheng <zhenglifeng1@huawei.com>,
Pierre Gondois <pierre.gondois@arm.com>,
Sumit Gupta <sumitg@nvidia.com>,
Sudeep Holla <sudeep.holla@arm.com>,
Ionela Voinescu <ionela.voinescu@arm.com>,
zhongqiu.han@oss.qualcomm.com
Subject: Re: [PATCH v3 1/3] ACPI: CPPC: Reject desired_perf reads on ACPI 6.6+
Date: Mon, 3 Aug 2026 15:44:02 +0100 [thread overview]
Message-ID: <c2082cfa-9473-448b-9efc-e70801bb2873@arm.com> (raw)
In-Reply-To: <CAJZ5v0iDuOJ2C_P8G9xD9BV7XEpQroyPecqM30ZxfEL=PzROAg@mail.gmail.com>
On 8/3/26 15:38, Rafael J. Wysocki (Intel) wrote:
>> When CPPC feedback counters cannot provide a usable sample, cppc-cpufreq
>> calls cppc_get_desired_perf() because some platforms repurpose Desired
>> Performance to report actual delivered performance.
>>
>> The fallback was added for platforms on which Desired Performance reflects
>> delivered performance. ACPI 6.6 defines the register as write-only, so
>> invoking that workaround on an ACPI 6.6 or later platform would require an
>> invalid register read.
>>
>> Make cppc_get_desired_perf() return -EOPNOTSUPP in that case. When checking
>> the FADT minor revision, mask off its upper errata-generation bits and
>> compare only the specification minor version.
> I'm wondering if the _CPC revision can be used for this instead of the
> spec revision?
>
> The _CPC revision changed from 3 to 4 between ACPI 6.5 and ACPI 6.6,
> so doing that should be straightforward.
Yup you're correct, much nicer, I'll fix that
next prev parent reply other threads:[~2026-08-03 14:44 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-29 10:02 [PATCHv2 0/3] ACPI: CPPC: Avoid Desired Performance reads on ACPI 6.6+ Christian Loehle
2026-07-29 10:02 ` [PATCHv2 1/3] ACPI: CPPC: Reject desired_perf " Christian Loehle
2026-07-31 10:45 ` Zhongqiu Han
2026-08-03 9:12 ` Christian Loehle
2026-07-31 20:52 ` Sumit Gupta
2026-07-29 10:02 ` [PATCHv2 2/3] ACPI: CPPC: Skip desired_perf read in cppc_get_perf() Christian Loehle
2026-07-31 12:38 ` Zhongqiu Han
2026-07-29 10:02 ` [PATCHv2 3/3] ACPI: CPPC: Stop reading desired_perf " Christian Loehle
2026-07-31 13:19 ` Zhongqiu Han
2026-08-03 10:02 ` [PATCH v3 0/3] ACPI: CPPC: Avoid Desired Performance reads on ACPI 6.6+ Christian Loehle
2026-08-03 10:02 ` [PATCH v3 1/3] ACPI: CPPC: Reject desired_perf " Christian Loehle
2026-08-03 14:38 ` Rafael J. Wysocki (Intel)
2026-08-03 14:44 ` Christian Loehle [this message]
2026-08-03 10:02 ` [PATCH v3 2/3] ACPI: CPPC: Skip desired_perf read in cppc_get_perf() Christian Loehle
2026-08-03 14:43 ` Rafael J. Wysocki (Intel)
2026-08-03 10:02 ` [PATCH v3 3/3] ACPI: CPPC: Stop reading desired_perf " Christian Loehle
2026-08-03 13:07 ` [PATCH v3 0/3] ACPI: CPPC: Avoid Desired Performance reads on ACPI 6.6+ Sumit Gupta
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