From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matthew Garrett Subject: Re: [REGRESSION/PATCH] acpi: blacklist win8 OSI for ASUS Zenbok Prime UX31A Date: Wed, 31 Jul 2013 06:14:22 +0100 Message-ID: <20130731051421.GA15766@srcf.ucam.org> References: <1375125658-1223-1-git-send-email-felipe.contreras@gmail.com> <3453253.oZLO1ChPbL@vostro.rjw.lan> <37178266.QXgbv9rq0i@vostro.rjw.lan> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from cavan.codon.org.uk ([93.93.128.6]:59851 "EHLO cavan.codon.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752988Ab3GaFO3 (ORCPT ); Wed, 31 Jul 2013 01:14:29 -0400 Content-Disposition: inline In-Reply-To: Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: Felipe Contreras Cc: "Rafael J. Wysocki" , Aaron Lu , linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org, Len Brown , Linus Torvalds On Tue, Jul 30, 2013 at 07:11:06PM -0500, Felipe Contreras wrote: > No, the ACPI driver is exposing a backlight interface, which has a > defined stable API. >>From the ACPI spec: 'The OEM may define the number 0 as "Zero brightness" that can mean to turn off the lighting (e.g. LCD panel backlight) in the device.' There's no mechanism for an OS to know whether or not a firmware implementation will actually turn the backlight off at 0, so there's no way the OS can define the lowest backlight state as anything other than "May or may not turn the screen off". If your userspace application depends on specific numbers having specific meanings, your userspace application is broken. Don't ascribe meanings to arbitrary values. -- Matthew Garrett | mjg59@srcf.ucam.org