From patchwork Sat Feb 11 03:17:10 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Zhang, Rui" X-Patchwork-Id: 13136807 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6C82AC636D3 for ; Sat, 11 Feb 2023 03:17:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229480AbjBKDRz (ORCPT ); Fri, 10 Feb 2023 22:17:55 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34234 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229498AbjBKDRy (ORCPT ); Fri, 10 Feb 2023 22:17:54 -0500 Received: from mga14.intel.com (mga14.intel.com [192.55.52.115]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C3ADC56EC6; Fri, 10 Feb 2023 19:17:43 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1676085463; x=1707621463; h=from:to:cc:subject:date:message-id:mime-version: content-transfer-encoding; bh=sb+EmESFN2NwMi7oUF5AK4fv80o+2wrYvPnvn9rSR1A=; b=mBu3WwJHYlx00v2WmeFJZQXG4ZpYvE2rVUrQsHFqEnxoDE/DZEF+Z2by KVGqOIyGMstF6kPF8bLPb9c2pD3s70vZI5vhXmzKVkFxyLfKSK2nauKAN 0/aOFUSvZG5IVWXCYDBR2vHh38FNKcYvfYrDGME4N4GevRc2u9T5TziH8 spxtIjxQDYevxHw3CZiHer84p/KA03yt7Ft/RwA9tBA9v6CtIuvwMKLkA cN57RenFWMywtzPBdHC3z8fO3kHr8sh89PbC/r73h5SsQBpVsNUlCP9dQ kANvgDFGYWcd1Qlr3dLaPh2rZri3d0/vhnNQ3yBpC7h2nYU/nBbbE6Nwq g==; X-IronPort-AV: E=McAfee;i="6500,9779,10617"; a="330586656" X-IronPort-AV: E=Sophos;i="5.97,287,1669104000"; d="scan'208";a="330586656" Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by fmsmga103.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 Feb 2023 19:17:23 -0800 X-IronPort-AV: E=McAfee;i="6500,9779,10617"; a="731919112" X-IronPort-AV: E=Sophos;i="5.97,287,1669104000"; d="scan'208";a="731919112" Received: from danma-mobl1.ccr.corp.intel.com (HELO rzhang1-DESK.intel.com) ([10.254.213.8]) by fmsmga008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 Feb 2023 19:17:22 -0800 From: Zhang Rui To: linux-pm@vger.kernel.org, rafael.j.wysocki@intel.com, daniel.lezcano@linaro.org Cc: linux-kernel@vger.kernel.org, srinivas.pandruvada@intel.com Subject: [PATCH V2] powercap/intel_rapl: Fix handling for large time window Date: Sat, 11 Feb 2023 11:17:10 +0800 Message-Id: <20230211031710.277459-1-rui.zhang@intel.com> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org When setting the power limit time window, software updates the 'y' bits and 'f' bits in the power limit register, and the value hardware takes follows the formula below Time window = 2 ^ y * (1 + f / 4) * Time_Unit When handling large time window input from userspace, using left shifting breaks in two cases, 1. when ilog2(value) is bigger than 31, in expression "1 << y", left shifting by more than 31 bits has undefined behavior. This breaks 'y'. For example, on an Alderlake platform, "1 << 32" returns 1. 2. when ilog2(value) equals 31, "1 << 31" returns negative value because '1' is recognized as signed int. And this breaks 'f'. Given that 'y' has 5 bits and hardware can never take a value larger than 31, fix the first problem by clamp the time window to the maximum possible value that the hardware can take. Fix the second problem by using unsigned bit left shift. Note that hardware has its own maximum time window limitation, which may be lower than the time window value retrieved from the power limit register. When this happens, hardware clamps the input to its maximum time window limitation. That is why a software clamp is preferred to handle the problem on hand. Signed-off-by: Zhang Rui --- Change since V1: 1. drop pr_warn message for bogus userspace input. 2. Add a comment when handling the large exponent. --- drivers/powercap/intel_rapl_common.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/drivers/powercap/intel_rapl_common.c b/drivers/powercap/intel_rapl_common.c index 26d00b1853b4..69526d21699d 100644 --- a/drivers/powercap/intel_rapl_common.c +++ b/drivers/powercap/intel_rapl_common.c @@ -999,7 +999,15 @@ static u64 rapl_compute_time_window_core(struct rapl_package *rp, u64 value, do_div(value, rp->time_unit); y = ilog2(value); - f = div64_u64(4 * (value - (1 << y)), 1 << y); + + /* + * The target hardware field has 7 bits, return all ones if + * the exponent is too large. + */ + if (y > 0x1f) + return 0x7f; + + f = div64_u64(4 * (value - (1ULL << y)), 1ULL << y); value = (y & 0x1f) | ((f & 0x3) << 5); } return value;