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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 7F631C433FF for ; Wed, 7 Aug 2019 11:41:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5D97321BF6 for ; Wed, 7 Aug 2019 11:41:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726873AbfHGLlV (ORCPT ); Wed, 7 Aug 2019 07:41:21 -0400 Received: from foss.arm.com ([217.140.110.172]:46970 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726860AbfHGLlV (ORCPT ); Wed, 7 Aug 2019 07:41:21 -0400 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 0860A28; Wed, 7 Aug 2019 04:41:21 -0700 (PDT) Received: from e107155-lin (e107155-lin.cambridge.arm.com [10.1.196.42]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 3B16A3F575; Wed, 7 Aug 2019 04:41:20 -0700 (PDT) Date: Wed, 7 Aug 2019 12:41:18 +0100 From: Sudeep Holla To: Al Stone Cc: linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org, "Rafael J . Wysocki" , Len Brown Subject: Re: [PATCH] ACPI / CPPC: do not require the _PSD method when using CPPC Message-ID: <20190807114118.GJ16546@e107155-lin> References: <20190805170338.29493-1-ahs3@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190805170338.29493-1-ahs3@redhat.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-acpi-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-acpi@vger.kernel.org On Mon, Aug 05, 2019 at 11:03:38AM -0600, Al Stone wrote: > According to the ACPI 6.3 specification, the _PSD method is optional > when using CPPC. The underlying assumption appears to be that each CPU > can change frequency independently from all other CPUs; _PSD is provided > to tell the OS that some processors can NOT do that. > > However, the acpi_get_psd() function returns -ENODEV if there is no _PSD > method present, or an ACPI error status if an error occurs when evaluating > _PSD, if present. This essentially makes _PSD mandatory when using CPPC, > in violation of the specification, and only on Linux. > > This has forced some firmware writers to provide a dummy _PSD, even though > it is irrelevant, but only because Linux requires it; other OSPMs follow > the spec. We really do not want to have OS specific ACPI tables, though. > > So, correct acpi_get_psd() so that it does not return an error if there > is no _PSD method present, but does return a failure when the method can > not be executed properly. This allows _PSD to be optional as it should > be. > Makes sense to me. FWIW, Reviewed-by: Sudeep Holla < sudeep.holla@arm.com> -- Regards, Sudeep