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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 5993BC2D0CE for ; Tue, 21 Jan 2020 16:19:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 39798217F4 for ; Tue, 21 Jan 2020 16:19:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729154AbgAUQTD (ORCPT ); Tue, 21 Jan 2020 11:19:03 -0500 Received: from mga12.intel.com ([192.55.52.136]:24252 "EHLO mga12.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726555AbgAUQTD (ORCPT ); Tue, 21 Jan 2020 11:19:03 -0500 X-Amp-Result: UNSCANNABLE X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by fmsmga106.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 21 Jan 2020 08:19:02 -0800 X-IronPort-AV: E=Sophos;i="5.70,346,1574150400"; d="scan'208";a="399712222" Received: from paasikivi.fi.intel.com ([10.237.72.42]) by orsmga005-auth.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 21 Jan 2020 08:18:58 -0800 Received: by paasikivi.fi.intel.com (Postfix, from userid 1000) id 4392B2072F; Tue, 21 Jan 2020 18:18:56 +0200 (EET) Date: Tue, 21 Jan 2020 18:18:56 +0200 From: Sakari Ailus To: "Rafael J. Wysocki" Cc: linux-i2c , Wolfram Sang , ACPI Devel Maling List , Bingbu Cao , linux-media@vger.kernel.org, Chiranjeevi Rapolu , Hyungwoo Yang , Bartosz Golaszewski , Arnd Bergmann , Linux Kernel Mailing List , Greg Kroah-Hartman , "Mani, Rajmohan" , Tomasz Figa Subject: Re: [PATCH v4 6/6] Documentation: ACPI: Document probe-low-power _DSD property Message-ID: <20200121161856.GZ5440@paasikivi.fi.intel.com> References: <20200121134157.20396-1-sakari.ailus@linux.intel.com> <20200121134157.20396-7-sakari.ailus@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-media-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org On Tue, Jan 21, 2020 at 05:09:44PM +0100, Rafael J. Wysocki wrote: > On Tue, Jan 21, 2020 at 2:41 PM Sakari Ailus > wrote: > > > > 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. > > Well, if you say "has been defined", you need to provide a pointer to > the definition document (a specification of some sort or similar). How about: s/has been defined/is used/ > > > + > > +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 > > -- > > 2.20.1 > > -- Sakari Ailus