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=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 A7F9AC433FF for ; Tue, 13 Aug 2019 21:59:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 827572067D for ; Tue, 13 Aug 2019 21:59:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726534AbfHMV7Y (ORCPT ); Tue, 13 Aug 2019 17:59:24 -0400 Received: from cloudserver094114.home.pl ([79.96.170.134]:58580 "EHLO cloudserver094114.home.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726155AbfHMV7X (ORCPT ); Tue, 13 Aug 2019 17:59:23 -0400 Received: from 79.184.255.155.ipv4.supernova.orange.pl (79.184.255.155) (HELO kreacher.localnet) by serwer1319399.home.pl (79.96.170.134) with SMTP (IdeaSmtpServer 0.83.275) id 470f59cd6541f77a; Tue, 13 Aug 2019 23:59:21 +0200 From: "Rafael J. Wysocki" To: Al Stone Cc: linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org, Len Brown Subject: Re: [PATCH] ACPI / CPPC: do not require the _PSD method when using CPPC Date: Tue, 13 Aug 2019 23:59:21 +0200 Message-ID: <521915646.RcUJINxfhL@kreacher> In-Reply-To: <20190805170338.29493-1-ahs3@redhat.com> References: <20190805170338.29493-1-ahs3@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Sender: linux-acpi-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-acpi@vger.kernel.org On Monday, August 5, 2019 7:03:38 PM CEST 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. > > Signed-off-by: Al Stone > Cc: Rafael J. Wysocki > Cc: Len Brown > --- > drivers/acpi/cppc_acpi.c | 11 +++++++---- > 1 file changed, 7 insertions(+), 4 deletions(-) > > diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c > index 15f103d7532b..e9ecfa13e997 100644 > --- a/drivers/acpi/cppc_acpi.c > +++ b/drivers/acpi/cppc_acpi.c > @@ -365,10 +365,13 @@ static int acpi_get_psd(struct cpc_desc *cpc_ptr, acpi_handle handle) > union acpi_object *psd = NULL; > struct acpi_psd_package *pdomain; > > - status = acpi_evaluate_object_typed(handle, "_PSD", NULL, &buffer, > - ACPI_TYPE_PACKAGE); > - if (ACPI_FAILURE(status)) > - return -ENODEV; > + if (acpi_has_method(handle, "_PSD")) { It would be better to compare the status below to AE_NOT_FOUND and return 0 if that's the case. A couple of code lines could be saved this way at least. > + status = acpi_evaluate_object_typed(handle, "_PSD", NULL, > + &buffer, ACPI_TYPE_PACKAGE); > + if (ACPI_FAILURE(status)) > + return -ENODEV; > + } else > + return 0; /* _PSD is optional */ > > psd = buffer.pointer; > if (!psd || psd->package.count != 1) { >