From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 0C14840E8E7; Mon, 3 Aug 2026 14:44:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785768248; cv=none; b=Kpv+y/puMRISjGHZ+JYzHMJtai+/4XbYFzGqH5wxtI6hMcGEbOdvrIFC4w51e5ZsPkdIHX3M3QDaQ41Spmh6vdqHEelba3vD35CxTWfQ7ycxt/qPWQspM/hFTFno1z48qfR2fwS7cKib1P90U3YaNYHseArSuhaEjekDhdMMRfc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785768248; c=relaxed/simple; bh=RCE4KSfoKwNfQQqMo0WObq9YygCPT+zkEvtfzR2db+o=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=lOMWbXCHlisV0CfDYOjpS/ioyUCkjGW9mL/0P+1GvfxyFOaWqhY07jB1dVpT0k7EoocYD0ZO1Oycadnk4GyhOcdGrCIB94TgmBMgD/sI2VPzFJtkO2H08AFqCRsymrAF488pUkLdA35KWT3Xm3ZT2lXqWaccoa7gVCgEEXCuzAI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=UTxq8Dpe; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="UTxq8Dpe" Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 47B2D143D; Mon, 3 Aug 2026 07:44:02 -0700 (PDT) Received: from [10.1.39.91] (e127648.arm.com [10.1.39.91]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8D1173F632; Mon, 3 Aug 2026 07:44:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1785768246; bh=RCE4KSfoKwNfQQqMo0WObq9YygCPT+zkEvtfzR2db+o=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=UTxq8Dpe1DfvtPj7XOtTSZl555t/REJYvlbcnaRoEEA+Inym4/1TPgK3YJOcDy4G4 TBMbPSIuA3tE5PuTMdCX+nOxBBnu5jKn7PCTMue+cxV7WLzAeqY9IwmHdWxzi3tUzg Pa3D6orWcODhMkxuaCNCiqnyZtSlYClz+QLLYOt4= Message-ID: Date: Mon, 3 Aug 2026 15:44:02 +0100 Precedence: bulk X-Mailing-List: linux-acpi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 1/3] ACPI: CPPC: Reject desired_perf reads on ACPI 6.6+ To: "Rafael J. Wysocki (Intel)" Cc: Viresh Kumar , linux-pm@vger.kernel.org, linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org, Jie Zhan , Lifeng Zheng , Pierre Gondois , Sumit Gupta , Sudeep Holla , Ionela Voinescu , zhongqiu.han@oss.qualcomm.com References: <20260729100245.2628302-1-christian.loehle@arm.com> <18ee922e97441b99b9ab346fe559d837d05eb5e7.1785749175.git.christian.loehle@arm.com> Content-Language: en-US From: Christian Loehle In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit 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