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=-16.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable 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 C959BC433DB for ; Thu, 28 Jan 2021 23:29:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9202C64DFA for ; Thu, 28 Jan 2021 23:29:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231792AbhA1X3Z (ORCPT ); Thu, 28 Jan 2021 18:29:25 -0500 Received: from mga06.intel.com ([134.134.136.31]:55147 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231645AbhA1X3T (ORCPT ); Thu, 28 Jan 2021 18:29:19 -0500 IronPort-SDR: +D+eCNrfk5MvQp6uFh98y8H3pkxk0rjufz1J18yq3jonoyC8WhIl0edG+3OgkczZif0LELRYRy LyWgt364o2Fw== X-IronPort-AV: E=McAfee;i="6000,8403,9878"; a="241856473" X-IronPort-AV: E=Sophos;i="5.79,383,1602572400"; d="scan'208";a="241856473" Received: from fmsmga003.fm.intel.com ([10.253.24.29]) by orsmga104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 28 Jan 2021 15:27:33 -0800 IronPort-SDR: hlr8EkA9peJ/k/cPmqW8tP0oIOQguldpmVA+yYsXDKWOaT8MJr+JcfiX2QqN9sXlLPhoFtmUzM zaLbHek99NSg== X-IronPort-AV: E=Sophos;i="5.79,383,1602572400"; d="scan'208";a="411236742" Received: from paasikivi.fi.intel.com ([10.237.72.42]) by fmsmga003-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 28 Jan 2021 15:27:29 -0800 Received: from punajuuri.localdomain (punajuuri.localdomain [192.168.240.130]) by paasikivi.fi.intel.com (Postfix) with ESMTP id C8A2521B1D; Fri, 29 Jan 2021 01:27:27 +0200 (EET) Received: from sailus by punajuuri.localdomain with local (Exim 4.92) (envelope-from ) id 1l5GhF-0004FG-ON; Fri, 29 Jan 2021 01:27:29 +0200 From: Sakari Ailus To: linux-i2c@vger.kernel.org Cc: Wolfram Sang , "Rafael J. Wysocki" , linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org, Greg Kroah-Hartman , rajmohan.mani@intel.com, Tomasz Figa , Bartosz Golaszewski , Bingbu Cao , Chiranjeevi Rapolu , Hyungwoo Yang , linux-media@vger.kernel.org Subject: [PATCH v9 3/7] Documentation: ACPI: Document _PRE object usage for enum power state Date: Fri, 29 Jan 2021 01:27:25 +0200 Message-Id: <20210128232729.16064-3-sakari.ailus@linux.intel.com> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200903081550.6012-1-sakari.ailus@linux.intel.com> References: <20200903081550.6012-1-sakari.ailus@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-i2c@vger.kernel.org Document the use of the _PRE object for setting desirable power state during probe. Signed-off-by: Sakari Ailus --- Documentation/firmware-guide/acpi/index.rst | 1 + .../firmware-guide/acpi/low-power-probe.rst | 51 +++++++++++++++++++ 2 files changed, 52 insertions(+) create mode 100644 Documentation/firmware-guide/acpi/low-power-probe.rst diff --git a/Documentation/firmware-guide/acpi/index.rst b/Documentation/firmware-guide/acpi/index.rst index f72b5f1769fb2..d02712acccbc0 100644 --- a/Documentation/firmware-guide/acpi/index.rst +++ b/Documentation/firmware-guide/acpi/index.rst @@ -25,5 +25,6 @@ ACPI Support acpi-lid lpit video_extension + low-power-probe extcon-intel-int3496 intel-pmc-mux diff --git a/Documentation/firmware-guide/acpi/low-power-probe.rst b/Documentation/firmware-guide/acpi/low-power-probe.rst new file mode 100644 index 0000000000000..3437f8c8f233a --- /dev/null +++ b/Documentation/firmware-guide/acpi/low-power-probe.rst @@ -0,0 +1,51 @@ +.. SPDX-License-Identifier: GPL-2.0 + +====================================== +Probing I²C devices in low power state +====================================== + +Introduction +============ + +In some cases it may be preferred to leave certain devices powered off for the +entire system bootup if powering on these devices has adverse side effects, +beyond just powering on the said device. + +How it works +============ + +The _PRE object that evaluates to integer 0 may be used to tell Linux that the +device should remain in the low power state during probe. If the driver +indicates its support for this by setting the I2C_DRV_FL_ALLOW_LOW_POWER_PROBE +flag in struct i2c_driver.flags field and the _PRE object evaluates to integer +0, the device will not be powered on for probe. + +The downside is that as the device is not powered on, even if there's a problem +with the device, the driver likely probes just fine but the first user will +find out the device doesn't work, instead of a failure at probe time. This +feature should thus be used sparingly. + +Example +======= + +An ASL example describing an ACPI device using this property looks like +this. Some objects not relevant from the example point of view have been +omitted. + +.. code-block:: text + + Device (CAM0) + { + Name (_HID, "SONY319A") + Name (_UID, Zero) + Name (_CRS, ResourceTemplate () + { + I2cSerialBus(0x0020, ControllerInitiated, 0x00061A80, + AddressingMode7Bit, "\\_SB.PCI0.I2C0", + 0x00, ResourceConsumer) + }) + Name (_PRE, 0, NotSerialized) + { + Return (0x0) + } + } -- 2.20.1