From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754900Ab3AaHbH (ORCPT ); Thu, 31 Jan 2013 02:31:07 -0500 Received: from mail-da0-f45.google.com ([209.85.210.45]:39119 "EHLO mail-da0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752521Ab3AaHbD (ORCPT ); Thu, 31 Jan 2013 02:31:03 -0500 Message-ID: <510A1DAC.1070106@gmail.com> Date: Thu, 31 Jan 2013 15:30:52 +0800 From: Mark Zhang User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130106 Thunderbird/17.0.2 MIME-Version: 1.0 To: Alexandre Courbot CC: Stephen Warren , Laurent Pinchart , Thierry Reding , Mark Zhang , Linux Kernel Mailing List , "linux-fbdev@vger.kernel.org" , "linux-tegra@vger.kernel.org" , "acourbot@nvidia.com" Subject: Re: [RFC 1/4] video: panel: add CLAA101WA01A panel support References: <1359514939-15653-1-git-send-email-acourbot@nvidia.com> <1359514939-15653-2-git-send-email-acourbot@nvidia.com> <5108C9C1.1090707@gmail.com> <51098064.7030902@wwwdotorg.org> <5109EA2A.8020204@gmail.com> <5109F916.8080404@gmail.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/31/2013 02:36 PM, Alexandre Courbot wrote: > On Thu, Jan 31, 2013 at 1:54 PM, Mark Zhang wrote: >> Display controller don't know whether the panel has EDID EEPROM but the >> panel driver knows. So why we need to make display controller queries >> EDID blindly? Since panel driver knows about all "video modes/panel >> size" stuffs, why not we let it handle all these things? > > The DC actually does know whether the connected panel supports EDID - > in this case, the output node will have a property for the DDC bus, > e.g. > > nvidia,ddc-i2c-bus = <&lcd_ddc>; > > If no DDC bus is specified or if transfer fails, the DC driver can > still query the panel driver for hardcoded modes. > Strictly speaking, according to my understanding, "nvidia,ddc-i2c-bus" means tegra has a hardware ddc channel, this doesn't mean we can get the EDID from this DDC surely. > Also passing a function pointer to get_modes() does not relief the DC > driver from probing for the DDC bus. You will still have to handle > both conditions (DDC bus present or not), the check will just be moved > into your callback function. > Yes. But panel driver decides whether the DDC probing is needed. If the panel has an EEPROM, it can call the function which display controller provides to do a DDC probing, it not, panel driver just ignores this function pointer and return the hardcoded modes directly. > Alex. >