From mboxrd@z Thu Jan 1 00:00:00 1970 From: Richard Purdie Subject: Re: [patch] added brightness feature to lcd class. Date: Mon, 09 Nov 2009 23:35:05 +0000 Message-ID: <1257809705.29038.82.camel@dax.rpnet.com> References: <90b950fc0911020050q3bc3fae8j954ec6ed73d79b5@mail.gmail.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <90b950fc0911020050q3bc3fae8j954ec6ed73d79b5@mail.gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" To: InKi Dae Cc: linux-fbdev-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org, Kyungmin Park , Andrew Morton , Pavel Machek On Mon, 2009-11-02 at 17:50 +0900, InKi Dae wrote: > This patch adds brightness feature to lcd class. > (kernel/driver/video/backlight/lcd.c) > > In the past, most of the lcd panels for embedded system was TFT-LCD > Panel needing backlight device. > But now AMOLED LCD Panel appeared so we should consider brightness > control for AMOLED Panel. > > For the time being, I used backlight fake driver for brightness > control of AMOLED LCD Panel. > But this way is not good, so I propose to add brightness feature to lcd class. > > For this, I attached patch file and if my proposal is approved > Then I will send s6e63m0 and tl2796 AMOLED lcd panel driver based on > lcd class modified soon. Pavel has a good point but let me try and explain it differently. The point of the backlight class is to expose a backlight brightness control to userspace in a consistent well defined way. Anyone wishing to write a piece of software to control the brightness of a backlight then only needs to support *one* interface. It is entirely accepted and normal that multiple "class" devices may appear in userspace for one piece of physical hardware. Your patch duplicates a userspace API and means any backlight application would have to look for *two* different interfaces. This is unacceptable. Why can't your driver just register a backlight interface and an LCD interface? I'd imagine your backlight and LCD can be powered on/off separately too. Please also cc: the backlight/lcd maintainer (me) on backlight/lcd patches in future. Andrew: Can you drop that patch from -mm please as I'm not convinced we need two backlight brightness interfaces around... Cheers, Richard