From patchwork Tue Jan 21 13:41:57 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Sakari Ailus X-Patchwork-Id: 194449 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=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH, MAILING_LIST_MULTI, SIGNED_OFF_BY, SPF_HELO_NONE, SPF_PASS, 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 3CC17C2D0DB for ; Tue, 21 Jan 2020 13:41:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1D47D2070C for ; Tue, 21 Jan 2020 13:41:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729186AbgAUNlv (ORCPT ); Tue, 21 Jan 2020 08:41:51 -0500 Received: from mga02.intel.com ([134.134.136.20]:28735 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729159AbgAUNlt (ORCPT ); Tue, 21 Jan 2020 08:41:49 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga003.fm.intel.com ([10.253.24.29]) by orsmga101.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 21 Jan 2020 05:41:49 -0800 X-IronPort-AV: E=Sophos;i="5.70,346,1574150400"; d="scan'208";a="275304981" Received: from paasikivi.fi.intel.com ([10.237.72.42]) by fmsmga003-auth.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 21 Jan 2020 05:41:45 -0800 Received: from punajuuri.localdomain (punajuuri.localdomain [192.168.240.130]) by paasikivi.fi.intel.com (Postfix) with ESMTP id 9EA1620B1D; Tue, 21 Jan 2020 15:41:39 +0200 (EET) Received: from sailus by punajuuri.localdomain with local (Exim 4.92) (envelope-from ) id 1ittn4-0005K5-1c; Tue, 21 Jan 2020 15:41:58 +0200 From: Sakari Ailus To: linux-i2c@vger.kernel.org Cc: Wolfram Sang , "Rafael J. Wysocki" , linux-acpi@vger.kernel.org, Bingbu Cao , linux-media@vger.kernel.org, Chiranjeevi Rapolu , Hyungwoo Yang , Bartosz Golaszewski , Arnd Bergmann , linux-kernel@vger.kernel.org, Greg Kroah-Hartman , rajmohan.mani@intel.com, Tomasz Figa Subject: [PATCH v4 6/6] Documentation: ACPI: Document probe-low-power _DSD property Date: Tue, 21 Jan 2020 15:41:57 +0200 Message-Id: <20200121134157.20396-7-sakari.ailus@linux.intel.com> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200121134157.20396-1-sakari.ailus@linux.intel.com> References: <20200121134157.20396-1-sakari.ailus@linux.intel.com> MIME-Version: 1.0 Sender: linux-acpi-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-acpi@vger.kernel.org Document the probe-low-power _DSD property and how it is used with I²C drivers. Signed-off-by: Sakari Ailus --- .../acpi/dsd/probe-low-power.rst | 28 +++++++++++++++++++ Documentation/firmware-guide/acpi/index.rst | 1 + 2 files changed, 29 insertions(+) create mode 100644 Documentation/firmware-guide/acpi/dsd/probe-low-power.rst diff --git a/Documentation/firmware-guide/acpi/dsd/probe-low-power.rst b/Documentation/firmware-guide/acpi/dsd/probe-low-power.rst new file mode 100644 index 0000000000000..e0343ffefe071 --- /dev/null +++ b/Documentation/firmware-guide/acpi/dsd/probe-low-power.rst @@ -0,0 +1,28 @@ +.. 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. The _DSD property +"probe-low-power" has been defined for this purpose. + +How it works +============ + +The property "probe-low-power" boolean property may be used to tell Linux +that the I²C framework should instruct the kernel ACPI framework to leave +the device in the low power state. If the driver indicates its support for +this in its struct i2c_driver.probe_low_power field and the +"probe-low-power" property is present, 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. diff --git a/Documentation/firmware-guide/acpi/index.rst b/Documentation/firmware-guide/acpi/index.rst index ad3b5afdae77e..4e4ac675c0ff8 100644 --- a/Documentation/firmware-guide/acpi/index.rst +++ b/Documentation/firmware-guide/acpi/index.rst @@ -11,6 +11,7 @@ ACPI Support dsd/graph dsd/data-node-references dsd/leds + dsd/probe-low-power enumeration osi method-customizing