From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.9 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5A895C433F4 for ; Wed, 29 Aug 2018 07:08:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 068B12084D for ; Wed, 29 Aug 2018 07:08:48 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=linaro.org header.i=@linaro.org header.b="UHwvBlsS" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 068B12084D Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linaro.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727667AbeH2LEM (ORCPT ); Wed, 29 Aug 2018 07:04:12 -0400 Received: from mail-wm0-f67.google.com ([74.125.82.67]:39114 "EHLO mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727198AbeH2LEM (ORCPT ); Wed, 29 Aug 2018 07:04:12 -0400 Received: by mail-wm0-f67.google.com with SMTP id q8-v6so4342075wmq.4 for ; Wed, 29 Aug 2018 00:08:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=from:to:cc:subject:date:message-id; bh=hGYHtsxP6qJIBkowwqLcEfY3ekjpkezQKD1guvAXw6I=; b=UHwvBlsSs4XACcwYmxO4D1gLt7a1zWh8LQs/0u7Sgx0bnfu8OPQPZWis4+vS3byauQ tbAK7E5BwoMZXaITymAjZBMfOTM8gkwK3uO89deOBLu7e6nrfA8e858huEvhLcv2QX/2 2KLtAXLxdAzBkqYtVQAcYeKpa3aR8yrWOHCoA= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id; bh=hGYHtsxP6qJIBkowwqLcEfY3ekjpkezQKD1guvAXw6I=; b=BnLR7wUsDE8uJ2cq1y6ZY5xD8mGTSOPR2fdPO4PWYisrWL1eZaTzOwY6ZtUqdJu4fy 9nBKkVRybx/vssjvC5ZQYp5QcDAQEF4hyncWIwhfZ/CabqVquMgVhLdUr2k/NA49ek+B TsHLJrsykwrjxrhAI3aTHGHPieJhbDp1o5sVD4Lm4k8fmhrfqRTuHI0QyYPUCAeh5QaE pAtLvZHo6TSxdBkceM/i84YN6HLCkUB3tvbwzmMrWeYj2841zfQm7tpk83bLXXq2Fyot 5rRaWTeFtJ17Yvg41MCBc561LwGEifmd712Y9iGEMoTYLtDE765vjCr+fNh1uhjYqDeX lrOw== X-Gm-Message-State: APzg51AxuinaJPqEkvw1/mYFBRs5g2ecSw7SJ7pBDuSxFVtHlW96/8QL IXuc9uj9S5/00kV7u1o4p0m3Yg== X-Google-Smtp-Source: ANB0VdbH+c3/oiUJ452jLs3yR/8xS/wiT6Qxc0hB1TmzKXFnos3bajaDM+RJ2aGUV0xxbGGciw1j7Q== X-Received: by 2002:a1c:ae8d:: with SMTP id x135-v6mr3412241wme.20.1535526523911; Wed, 29 Aug 2018 00:08:43 -0700 (PDT) Received: from localhost.localdomain ([2a01:e0a:f:6020:4c23:4749:7ea6:c5af]) by smtp.gmail.com with ESMTPSA id 34-v6sm4984283wra.20.2018.08.29.00.08.42 (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Wed, 29 Aug 2018 00:08:43 -0700 (PDT) From: Vincent Guittot To: robh+dt@kernel.org, mark.rutland@arm.com, devicetree@vger.kernel.org, punit.agrawal@arm.com Cc: edubezval@gmail.com, viresh.kumar@linaro.org, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, Vincent Guittot Subject: [PATCH v2] dt-binding: arm/cpus.txt: fix dynamic-power-coefficient unit Date: Wed, 29 Aug 2018 09:08:38 +0200 Message-Id: <1535526518-29022-1-git-send-email-vincent.guittot@linaro.org> X-Mailer: git-send-email 2.7.4 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The unit of dynamic-power-coefficient is described as mW/MHz/uV^2 whereas its usage in the code assumes that unit is uW/MHz/V^2 In drivers/thermal/cpu_cooling.c, the code is : power = (u64)capacitance * freq_mhz * voltage_mv * voltage_mv; do_div(power, 1000000000); which can be summarized as : power (mW) = capacitance * freq_mhz/1000 * (voltage_mv/1000)^2 or power (mW) = (capacitance * freq_mhz * (voltage_mv/1000)^2) / 1000 then power (mW) = power (uW) / 1000 so power (uW) = capacitance * freq_mhz * (voltage_mv/1000)^2 Furthermore, if we test basic values like : voltage_mv = 1000mV = 1V freq_mhz = 1000Mhz The minimum possible power, when dynamic-power-coefficient equals 1, will be with current unit: min power = 1 * 1000 * (1000000)^2 = 10^15 mW which is not realistic With the unit used by the code, the min power is min power = 1 * 1000 * 1^2 = 1000uW = 1mW which is far more realistic Signed-off-by: Vincent Guittot --- Documentation/devicetree/bindings/arm/cpus.txt | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/Documentation/devicetree/bindings/arm/cpus.txt b/Documentation/devicetree/bindings/arm/cpus.txt index 29e1dc5..71d8cd0 100644 --- a/Documentation/devicetree/bindings/arm/cpus.txt +++ b/Documentation/devicetree/bindings/arm/cpus.txt @@ -274,7 +274,7 @@ described below. Usage: optional Value type: Definition: A u32 value that represents the running time dynamic - power coefficient in units of mW/MHz/uV^2. The + power coefficient in units of uW/MHz/V^2. The coefficient can either be calculated from power measurements or derived by analysis. @@ -285,7 +285,7 @@ described below. Pdyn = dynamic-power-coefficient * V^2 * f - where voltage is in uV, frequency is in MHz. + where voltage is in V, frequency is in MHz. Example 1 (dual-cluster big.LITTLE system 32-bit): -- 2.7.4