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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 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 ADE4EC433FF for ; Tue, 13 Aug 2019 14:00:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 87135206C2 for ; Tue, 13 Aug 2019 14:00:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729038AbfHMOA7 (ORCPT ); Tue, 13 Aug 2019 10:00:59 -0400 Received: from mail-ot1-f65.google.com ([209.85.210.65]:33422 "EHLO mail-ot1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727724AbfHMOA7 (ORCPT ); Tue, 13 Aug 2019 10:00:59 -0400 Received: by mail-ot1-f65.google.com with SMTP id q20so19894321otl.0 for ; Tue, 13 Aug 2019 07:00:58 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:reply-to:subject:to:cc:references:from :organization:message-id:date:user-agent:mime-version:in-reply-to :content-language:content-transfer-encoding; bh=Idmq9Ela+dAzEHfkXXgCpLtAAlGcGfcAq5nVbCa7csQ=; b=b8b9mBNdUe1FswywPoKhLuorcUV4N5oBuoc+yzZSu36Lm/idZJ73Hf87dA37ItLPFS iCUI6v7lLbKA3R7HdDeh0c9EXRqnbYKxADOfp8x+lZSbBiuNA6ZkqPucaSvf1M9SKSoZ WLfoPpEx9Zxzp6QujXCgPXGVer8iL7PccH3vpCeJh8m4GrU8GPWTgAjpQuJTblkwsv9a rTT/qEwXiHzMfFZLzXas5dc/b/a2xixGMgnep6kONKN5Si4bJ57Zq7NojvezRHuRGUAU bSi9sPkx8JLONTmpmJakt3c/I9ZyX5Ide+J4SYihgzWFkJBCcw4rBtnuaHbvhtpsLU3V gbow== X-Gm-Message-State: APjAAAUmtcNcoaq/F2EptrpEiis8jmqzFVKTplgnHMAkOypmXmUQcnDs KWAlWYJCg6iLXv9ZrXJv9N02bA== X-Google-Smtp-Source: APXvYqxcHGhMgSCYok78PR7yvPzptpT3YD5UEkb319vYu7Xf5HBHeeR+wgip9mNwQL4ltLXlzzt+uw== X-Received: by 2002:a02:37c6:: with SMTP id r189mr32472750jar.118.1565704858100; Tue, 13 Aug 2019 07:00:58 -0700 (PDT) Received: from masetto.ahs3 (c-67-165-232-89.hsd1.co.comcast.net. [67.165.232.89]) by smtp.gmail.com with ESMTPSA id v13sm10600441iol.60.2019.08.13.07.00.57 (version=TLS1_3 cipher=AEAD-AES128-GCM-SHA256 bits=128/128); Tue, 13 Aug 2019 07:00:57 -0700 (PDT) Reply-To: ahs3@redhat.com Subject: Re: [PATCH] ACPI / CPPC: do not require the _PSD method when using CPPC To: linux-acpi@vger.kernel.org Cc: linux-kernel@vger.kernel.org, "Rafael J . Wysocki" , Len Brown References: <20190805170338.29493-1-ahs3@redhat.com> From: Al Stone Organization: Red Hat, Inc. Message-ID: Date: Tue, 13 Aug 2019 08:00:56 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190805170338.29493-1-ahs3@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-acpi-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-acpi@vger.kernel.org On 8/5/19 11:03 AM, 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")) { > + 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) { > Rafael, Any other comments? Would it be possible to pull this into an -rc? I'd really like to avoid anyone else having to ship Linux-specific DSDTs and SSDTs. Thanks. -- ciao, al ----------------------------------- Al Stone Software Engineer Red Hat, Inc. ahs3@redhat.com -----------------------------------