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=-7.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS 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 D1552C2D0CE for ; Tue, 21 Jan 2020 16:09:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A4557217F4 for ; Tue, 21 Jan 2020 16:09:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1579622996; bh=R1eEXnFyip2fv+0SKvdc1gYFUwou2ZbCerOxCchGwKs=; h=References:In-Reply-To:From:Date:Subject:To:Cc:List-ID:From; b=s5GBtR5BNaE+aTYlZcQs4vgGqHYX88DH837ct9EdnbCo5FK0por+2FuGptRxmMaRR IAOrMhPbQ0zJ2Qqx1zAlCBJLiYVYSKgFgJ8/SiRY+DuAqVlHhRiHLSTDLIf2LbtsbS tuAIPWjlksZWyhyrP2bmfywz2kcCs7v8trbOjonk= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729030AbgAUQJ4 convert rfc822-to-8bit (ORCPT ); Tue, 21 Jan 2020 11:09:56 -0500 Received: from mail-oi1-f195.google.com ([209.85.167.195]:35365 "EHLO mail-oi1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726555AbgAUQJ4 (ORCPT ); Tue, 21 Jan 2020 11:09:56 -0500 Received: by mail-oi1-f195.google.com with SMTP id k4so3065190oik.2; Tue, 21 Jan 2020 08:09:55 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc:content-transfer-encoding; bh=WN3HnFcBCL605feigra+tO+syYiJ3DTCVagEeBtU1zE=; b=pY4OHNDSoG/gfHQ3/qw2TD+J856e/Wn44+XpHnemeKDgaqkXMcwLSOtQ/dpIvDDDca ERFtnEP2fx44/QU3K0VQvPC1AM5mBMLxQwaohYKuwtPm78pLPTFFE7q1isROpOp5nvKX 30IJDN4D7g5xCuhD/UXfW7+qd+SwFinlxl1sOwij2CzNDZ7kExlbameD0U4iPzDGDYry pDlenB/+gaWWHCOQZsATobEKXhPrWRxwtk9q28HODwy+Lt4UzU4L8l7b9PYe3MYIOoLn sxwfB5YT0JZ00Bb+OxS/LGNO5by2al81nCcgouhVrV97lQ2UIsx4bXvihBrvvlW7ih63 srww== X-Gm-Message-State: APjAAAV8FBC5bdbZdbGgMK6GzfMvm5p8vYbVAPY4LMPHvmz9gaJ9HLik 8/1mvUZNIKYmRtVcui17jM2oHr/WXj36wql+yhU= X-Google-Smtp-Source: APXvYqyFb+SVqk9VpuQeRnX96Fhq2Tj/z5ocFPbgiTRYbyNkL8iXSmsSj+ocij4JKF0ClJaAcyrt26a2HU5ddNAJ9aE= X-Received: by 2002:a54:4e96:: with SMTP id c22mr3615375oiy.110.1579622995229; Tue, 21 Jan 2020 08:09:55 -0800 (PST) MIME-Version: 1.0 References: <20200121134157.20396-1-sakari.ailus@linux.intel.com> <20200121134157.20396-7-sakari.ailus@linux.intel.com> In-Reply-To: <20200121134157.20396-7-sakari.ailus@linux.intel.com> From: "Rafael J. Wysocki" Date: Tue, 21 Jan 2020 17:09:44 +0100 Message-ID: Subject: Re: [PATCH v4 6/6] Documentation: ACPI: Document probe-low-power _DSD property To: Sakari Ailus Cc: linux-i2c , Wolfram Sang , "Rafael J. Wysocki" , 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 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT Sender: linux-acpi-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-acpi@vger.kernel.org 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 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 >