From patchwork Tue Sep 1 21:03:33 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Sakari Ailus X-Patchwork-Id: 11749489 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 2F918618 for ; Tue, 1 Sep 2020 21:03:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 22310208CA for ; Tue, 1 Sep 2020 21:03:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728799AbgIAVDh (ORCPT ); Tue, 1 Sep 2020 17:03:37 -0400 Received: from mga12.intel.com ([192.55.52.136]:23422 "EHLO mga12.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728098AbgIAVDf (ORCPT ); Tue, 1 Sep 2020 17:03:35 -0400 IronPort-SDR: +Mr+6vVp5TJcvdxd+Pd3f/P+4f6nPYNghpaOWlLO115JuqYUs+Q5Z+8QnWapQEHZRPjVuPZK6H z8D2hMACKukw== X-IronPort-AV: E=McAfee;i="6000,8403,9731"; a="136786013" X-IronPort-AV: E=Sophos;i="5.76,380,1592895600"; d="scan'208";a="136786013" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by fmsmga106.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 01 Sep 2020 14:03:35 -0700 IronPort-SDR: XEZWkK12m3NRurgxOZ0Ler6s1GjrNyuUSTV2HECMOdTxCR64tDMXiREISajPYuDtfexl3iBdJk Xnq+rSUltiSA== X-IronPort-AV: E=Sophos;i="5.76,380,1592895600"; d="scan'208";a="477343364" Received: from paasikivi.fi.intel.com ([10.237.72.42]) by orsmga005-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 01 Sep 2020 14:03:31 -0700 Received: from punajuuri.localdomain (punajuuri.localdomain [192.168.240.130]) by paasikivi.fi.intel.com (Postfix) with ESMTP id A383722AF1; Wed, 2 Sep 2020 00:03:24 +0300 (EEST) Received: from sailus by punajuuri.localdomain with local (Exim 4.92) (envelope-from ) id 1kDDRF-0002Da-HG; Wed, 02 Sep 2020 00:03:33 +0300 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 v7 6/6] Documentation: ACPI: Document allow-low-power-probe _DSD property Date: Wed, 2 Sep 2020 00:03:33 +0300 Message-Id: <20200901210333.8462-7-sakari.ailus@linux.intel.com> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200901210333.8462-1-sakari.ailus@linux.intel.com> References: <20200901210333.8462-1-sakari.ailus@linux.intel.com> MIME-Version: 1.0 Sender: linux-media-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-media@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