Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756159AbXJ1XNE (ORCPT ); Sun, 28 Oct 2007 19:13:04 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753187AbXJ1XMx (ORCPT ); Sun, 28 Oct 2007 19:12:53 -0400 Received: from mailgw2.3essentials.com ([66.179.153.59]:3811 "EHLO mailgw2.3essentials.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753566AbXJ1XMw (ORCPT ); Sun, 28 Oct 2007 19:12:52 -0400 Message-ID: <4725174F.40701@antonello.org> Date: Mon, 29 Oct 2007 00:12:15 +0100 From: "lists@antonello.org" User-Agent: Thunderbird 2.0.0.6 (X11/20070728) MIME-Version: 1.0 To: Matt Domsch CC: linux-kernel@vger.kernel.org Subject: Re: [PATCH] Dell laptop backlight driver References: <4724B4F5.80004@antonello.org> <20071028161955.GF23359@auslistsprd01.us.dell.com> <4724CF9F.6050908@antonello.org> <20071028192031.GA11442@auslistsprd01.us.dell.com> In-Reply-To: <20071028192031.GA11442@auslistsprd01.us.dell.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3424 Lines: 75 Matt Domsch wrote: > On Sun, Oct 28, 2007 at 07:06:23PM +0100, lists@antonello.org wrote: >> Matt Domsch wrote: >>> On Sun, Oct 28, 2007 at 05:12:37PM +0100, jack@antonello.org wrote: >>>> Hello, >>>> this driver implements backlight control on Dell laptops >>>> which use SMI for changing brightness levels. >>>> >>>> The driver is INCOMPLETE since it is unable to probe some required >>>> parameters >>>> in order to perform backlight control. Such parameters are found in a Dell >>>> proprietary DMI table which should be parsed. For now external tools may >>>> be >>>> used to find these parameters by hand. So if you intend to try this out, >>>> FIRST write your laptop model parameters correctly inside the source code >>>> as explained in Documentation/dell-laptop.txt. >>>> >>>> Parts of this driver may also be used to provide additional >>>> functionalities >>>> similarly to the drivers/misc/*-laptop.c drivers. >>> Why is this better done in the kernel rather than in userspace with >>> libsmbios as you've noted? >>> >> I had to do a kernelspace driver for controlling the backlight. This >> was part of a college project assignment. In order for it to be valid >> for an operating system course, it had to be in kernelspace (not >> Unix programming) :). >> >> As i mentioned that can be done in userspace and it IS sensible to do >> so. I know that the code which was already written for Dell implied >> a userspace approach, but i simply had no choice. >> >> I also don't expect this driver to become mainstream, but since i have >> written it, other people might want to have a look at it. > > OK, that's fair. > > >> Finally i really don't think there's any sensible way of implementing >> Linux LCD Backlight Abstraction relying on a userspace application. >> That would mean the kernel calling userspace code to change the >> brightness, then this latter code would again call the kernel to trigger >> a SMI and so on. That's just not a good design. I think a userspace >> solution implies choosing NOT to implement the LCD Abstraction. Causing >> Dell laptops to be treated differently from other machines (as they are >> not compliant with Linux's own interface). > > I've had this discussion on lkml before. Short story is, until Dell > laptops implement the ACPI methods that the backlight API expects, the > only sane way to do it is to let libsmbios handle it. Moving the > fairly large and complex libsmbios into the kernel isn't a good idea > (imho). > > > I agree. The problem is that Dell's DMI tables are not defined in the SMBIOS standard. Thus getting the parameters required for the backlight control (io port, io code, location) needs to be dealt with specifically. Plus DMI is not as comprehensively supported as ACPI is under Linux. I think reading Dell's tables to find out backlight parameters in kernelspace is possible. Unfortunately it would require a significant amount of brand new code to be written. And i'm not sure it is worth the effort. Libsmbios is big and complex because it is written in proficient C++ with lots of OO abstraction. It is also portable. But the task accomplished is simple in principle. jacopo - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/