From patchwork Wed Aug 26 11:54:32 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Sakari Ailus X-Patchwork-Id: 251698 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=-12.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH, MAILING_LIST_MULTI, SIGNED_OFF_BY, SPF_HELO_NONE, SPF_PASS, 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 458CDC433E1 for ; Wed, 26 Aug 2020 11:51:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1F2562080C for ; Wed, 26 Aug 2020 11:51:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729057AbgHZLvw (ORCPT ); Wed, 26 Aug 2020 07:51:52 -0400 Received: from mga01.intel.com ([192.55.52.88]:45642 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729139AbgHZLvb (ORCPT ); Wed, 26 Aug 2020 07:51:31 -0400 IronPort-SDR: uhORCpgCt4K2QtCJXkYwrK8+AAfHSAWOhO34i0OVSPGtdxOTED7D51nTPSRfYeAzZmHq7cXLrH 6VFNurD/xtLg== X-IronPort-AV: E=McAfee;i="6000,8403,9724"; a="174324059" X-IronPort-AV: E=Sophos;i="5.76,355,1592895600"; d="scan'208";a="174324059" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga006.fm.intel.com ([10.253.24.20]) by fmsmga101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 26 Aug 2020 04:51:31 -0700 IronPort-SDR: NWN7TnPX9XtMQcf/dtvFTwu+mQMQBbsCSntQBSpupBkvPnyVaLhsK94SEcTf0+r42c/H5S04zH 1ceirtnYBRVg== X-IronPort-AV: E=Sophos;i="5.76,355,1592895600"; d="scan'208";a="499691480" Received: from paasikivi.fi.intel.com ([10.237.72.42]) by fmsmga006-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 26 Aug 2020 04:51:28 -0700 Received: from punajuuri.localdomain (punajuuri.localdomain [192.168.240.130]) by paasikivi.fi.intel.com (Postfix) with ESMTP id 8CEB820E50; Wed, 26 Aug 2020 14:50:51 +0300 (EEST) Received: from sailus by punajuuri.localdomain with local (Exim 4.92) (envelope-from ) id 1kAu0e-0001bY-Ue; Wed, 26 Aug 2020 14:54:32 +0300 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 , "Qiu, Tian Shu" Subject: [PATCH v6 6/6] Documentation: ACPI: Document allow-low-power-probe _DSD property Date: Wed, 26 Aug 2020 14:54:32 +0300 Message-Id: <20200826115432.6103-7-sakari.ailus@linux.intel.com> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200826115432.6103-1-sakari.ailus@linux.intel.com> References: <20200826115432.6103-1-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/allow-low-power-probe.rst | 28 +++++++++++++++++++ Documentation/firmware-guide/acpi/index.rst | 1 + 2 files changed, 29 insertions(+) create mode 100644 Documentation/firmware-guide/acpi/dsd/allow-low-power-probe.rst diff --git a/Documentation/firmware-guide/acpi/dsd/allow-low-power-probe.rst b/Documentation/firmware-guide/acpi/dsd/allow-low-power-probe.rst new file mode 100644 index 0000000000000..6fcc89162b898 --- /dev/null +++ b/Documentation/firmware-guide/acpi/dsd/allow-low-power-probe.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. Linux recognizes the _DSD property +"allow-low-power-probe" that can be used for this purpose. + +How it works +============ + +The property "allow-low-power-probe" 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 by +setting the I2C_DRV_FL_ALLOW_LOW_POWER_PROBE flag in struct i2c_driver.flags +field and the "allow-low-power-probe" 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..0070fcde9e669 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/allow-low-power-probe enumeration osi method-customizing