From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9420EC4332F for ; Tue, 19 Oct 2021 15:57:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7975961038 for ; Tue, 19 Oct 2021 15:57:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232833AbhJSQAD (ORCPT ); Tue, 19 Oct 2021 12:00:03 -0400 Received: from relay1-d.mail.gandi.net ([217.70.183.193]:48339 "EHLO relay1-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231495AbhJSQAD (ORCPT ); Tue, 19 Oct 2021 12:00:03 -0400 Received: (Authenticated sender: thomas.petazzoni@bootlin.com) by relay1-d.mail.gandi.net (Postfix) with ESMTPSA id 655E7240006; Tue, 19 Oct 2021 15:57:47 +0000 (UTC) Date: Tue, 19 Oct 2021 17:57:46 +0200 From: Thomas Petazzoni To: Andrew Lunn Cc: =?UTF-8?B?S8O2cnk=?= Maincent , Geert Uytterhoeven , netdev , Linux-Renesas , Linux Kernel Mailing List , Sergey Shtylyov , "David S. Miller" , Jakub Kicinski , Lad Prabhakar , Biju Das , Sergei Shtylyov , Adam Ford , Yoshihiro Shimoda , Yang Yingliang Subject: Re: [PATCH] net: renesas: Fix rgmii-id delays Message-ID: <20211019175746.11b388ce@windsurf> In-Reply-To: References: <20211019145719.122751-1-kory.maincent@bootlin.com> <20211019173520.0154a8cb@kmaincent-XPS-13-7390> Organization: Bootlin X-Mailer: Claws Mail 3.18.0 (GTK+ 2.24.33; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Tue, 19 Oct 2021 17:41:49 +0200 Andrew Lunn wrote: > > When people update the kernel version don't they update also the devicetree? > > DT is ABI. Driver writers should not break old blobs running on new > kernels. Often the DT blob is updated with the kernel, but it is not > required. It could be stored in a hard to reach place, shared with > u-boot etc. Right, but conversely if someone reads the DT bindings that exists today, specifies phy-mode = "rgmii-rxid" or phy-mmode = "rmgii-txid", this person will get incorrect behavior. Sure a behavior that is backward compatible with older DTs, but a terribly wrong one when you write a new DT and read the DT binding documentation. This is exactly the problem that happened to us. I know that those properties are considered obsolete, but even though they are considered as such, they are still supported, but for this particular MAC driver, with an inverted meaning compared to what the DT binding documentation says. What wins: DT ABI backward compatibility, or correctness of the DT binding ? :-) Best regards, Thomas -- Thomas Petazzoni, co-owner and CEO, Bootlin Embedded Linux and Kernel engineering and training https://bootlin.com