From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752135AbaIYGmp (ORCPT ); Thu, 25 Sep 2014 02:42:45 -0400 Received: from metis.ext.pengutronix.de ([92.198.50.35]:46664 "EHLO metis.ext.pengutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751978AbaIYGmn (ORCPT ); Thu, 25 Sep 2014 02:42:43 -0400 Date: Thu, 25 Sep 2014 08:42:42 +0200 From: Sascha Hauer To: Nikita Yushchenko Cc: devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, Gennady Kuznetsov , Aleksey Makarov Subject: Re: Device tree vs hardware configurations Message-ID: <20140925064242.GJ4992@pengutronix.de> References: <5421B4B0.1020306@dev.rtsoft.ru> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5421B4B0.1020306@dev.rtsoft.ru> X-Sent-From: Pengutronix Hildesheim X-URL: http://www.pengutronix.de/ X-IRC: #ptxdist @freenode X-Accept-Language: de,en X-Accept-Content-Type: text/plain X-Uptime: 08:21:34 up 14 days, 23:09, 54 users, load average: 0.07, 0.06, 0.08 User-Agent: Mutt/1.5.21 (2010-09-15) X-SA-Exim-Connect-IP: 2001:67c:670:100:1d::c0 X-SA-Exim-Mail-From: sha@pengutronix.de X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: linux-kernel@vger.kernel.org Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Nikita, On Tue, Sep 23, 2014 at 09:58:08PM +0400, Nikita Yushchenko wrote: > Hi > > I'm currently forward-porting a BSP for imx6-based custom board from > pre-devicetree kernel to modern kernel. > > In old BSP there was a board setup file, that registered all board's > devices. For new BSP, I need to replace that with device tree based > solution. > > However, old BSP used conditional code to register devices > differently based on GPIO inputs and on kernel command line. This > approach was used to > > - handle board's jumper that switches SPI CS lines: current jumper > setting is available over gpio, depending on that old BSP registered > chips differently, > > - handle different i2c connections on different board revisions: > board has 5 i2c busses with quite a few devices connected, these > busses are routed to different hardware busses on different board > revisions, board revision could be read over gpios. > > - handle different possible display connections (lvds vs lcd, 6bit > vs 8bit hw interface) based on kernel command line options > > - handle different possible camera connections by registered camera > differently based on kernel command line option > > ... and more, > > > Device tree describes hardware unconditionally. I already have to > provide 2 dts files for imx6q and imx6dl based setups (both just > include a common dtsi) ... But providing separate dts file for > every possible hardware configuration will result into 2^n device > trees, which is inconvenient visible regression against old BSP that > "just worked" on all hardware configurations. > > > Is there a sane way to handle hardware configurations like above in > device tree based kernel? This depends on your definition of sane, but here the options I know of: - Let the bootloader modify the device tree based on the GPIOs. This seems doable in new projects, but not when you want to keep the old bootloader. - Use device tree overlays in the Kernel which is something Pantelis Antoniou works on. I think the intention here is more to plug a daughter board to a CPU board. I don't know how good this works when you have to manipulate many different places in the device tree. - I heard people working on a shim to place between bootloader and kernel. The shim translates the bootloader information into the device tree. I can't remember who it was though. For going this way I wouldn't rewrite the shim but use barebox instead of course ;) BTW where do the command line options in your setup come from? Are they autogenerated from other informations in the bootloader or are they entered there by a user? Sascha -- Pengutronix e.K. | | Industrial Linux Solutions | http://www.pengutronix.de/ | Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |