From patchwork Fri Feb 5 13:25:01 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Sakari Ailus X-Patchwork-Id: 377291 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=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 9948BC433E6 for ; Fri, 5 Feb 2021 22:42:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 68E2464FEB for ; Fri, 5 Feb 2021 22:42:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230034AbhBEWl6 (ORCPT ); Fri, 5 Feb 2021 17:41:58 -0500 Received: from mga12.intel.com ([192.55.52.136]:61266 "EHLO mga12.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229586AbhBENcm (ORCPT ); Fri, 5 Feb 2021 08:32:42 -0500 IronPort-SDR: leOgntPwmnYSChsVUgDrn8OD1MXye/2Cb3nWWCKkc3ZO7mTk9XPjYZEBNPevcZjf7/2MFNsv2/ ioY6CRNZnHJA== X-IronPort-AV: E=McAfee;i="6000,8403,9885"; a="160589445" X-IronPort-AV: E=Sophos;i="5.81,154,1610438400"; d="scan'208";a="160589445" Received: from orsmga002.jf.intel.com ([10.7.209.21]) by fmsmga106.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Feb 2021 05:24:57 -0800 IronPort-SDR: tsFjqPXflkKVrUq2GBeFF08LfZfad/IyEnl8GBObhJxqdcToZHgFwnVZJxHtPExxEYBvyftzFA jY9NJToJRXJQ== X-IronPort-AV: E=Sophos;i="5.81,154,1610438400"; d="scan'208";a="373390607" Received: from paasikivi.fi.intel.com ([10.237.72.42]) by orsmga002-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Feb 2021 05:24:53 -0800 Received: from punajuuri.localdomain (punajuuri.localdomain [192.168.240.130]) by paasikivi.fi.intel.com (Postfix) with ESMTP id 90B8420D38; Fri, 5 Feb 2021 15:24:51 +0200 (EET) Received: from sailus by punajuuri.localdomain with local (Exim 4.92) (envelope-from ) id 1l816f-0005GL-C1; Fri, 05 Feb 2021 15:25:05 +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 v10 3/7] Documentation: ACPI: Document _DSE object usage for enum power state Date: Fri, 5 Feb 2021 15:25:01 +0200 Message-Id: <20210205132505.20173-4-sakari.ailus@linux.intel.com> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20210205132505.20173-1-sakari.ailus@linux.intel.com> References: <20210205132505.20173-1-sakari.ailus@linux.intel.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org Document the use of the _DSE object for setting desirable power state during probe. Signed-off-by: Sakari Ailus Reviewed-by: Tomasz Figa --- Documentation/firmware-guide/acpi/index.rst | 1 + .../firmware-guide/acpi/low-power-probe.rst | 69 +++++++++++++++++++ 2 files changed, 70 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..b96804d959a6c --- /dev/null +++ b/Documentation/firmware-guide/acpi/low-power-probe.rst @@ -0,0 +1,69 @@ +.. 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 _DSE (Device State for Enumeration) object that evaluates to integer 0 may +be used to tell Linux the highest allowed D state for a device 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 +_DSE object evaluates to integer higher than the D state of the device, the +device will not be powered on (put in D0 state) for probe. + +The D states and thus also the allowed values for _DSE are listed below. Refer +to [1] for more information on device power states. + +.. code-block:: text + + Number State Description + 0 D0 Device fully powered on + 1 D1 + 2 D2 + 3 D3hot + 4 D3cold Off + +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. + +References +========== + +[1] https://uefi.org/specifications/ACPI/6.4/02_Definition_of_Terms/Definition_of_Terms.html#device-power-state-definitions + +Example +======= + +An ASL example describing an ACPI device using _DSE object to tell Operating +System the device should remain powered off during probe 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 (_DSE, 0, NotSerialized) + { + Return (0x4) + } + }