Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752299AbdGDXnR (ORCPT ); Tue, 4 Jul 2017 19:43:17 -0400 Received: from smtp2-g21.free.fr ([212.27.42.2]:54748 "EHLO smtp2-g21.free.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752203AbdGDXnQ (ORCPT ); Tue, 4 Jul 2017 19:43:16 -0400 Subject: Re: [PATCH v9 2/3] PCI: Add tango PCIe host bridge support To: Bjorn Helgaas Cc: Marc Gonzalez , Marc Zyngier , Thomas Gleixner , linux-pci , Linux ARM , LKML , Thibaud Cornic , Mark Rutland , Ard Biesheuvel , Greg Kroah-Hartman References: <987fac41-80dc-f1d0-ec0b-91ae57b91bfd@sigmadesigns.com> <20170702231811.GJ18324@bhelgaas-glaptop.roam.corp.google.com> <79382219-c730-da78-3e5f-5abf3173d7ac@sigmadesigns.com> <20170703134031.GG13824@bhelgaas-glaptop.roam.corp.google.com> <16622817-8ccd-107b-be08-676b576f6e8a@sigmadesigns.com> <20170704155855.GI13824@bhelgaas-glaptop.roam.corp.google.com> From: Mason Message-ID: <877fefdf-969d-bc46-3233-f988ccfe4c74@free.fr> Date: Wed, 5 Jul 2017 01:42:47 +0200 User-Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:52.0) Gecko/20100101 Firefox/52.0 SeaMonkey/2.49.1 MIME-Version: 1.0 In-Reply-To: <20170704155855.GI13824@bhelgaas-glaptop.roam.corp.google.com> Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 736 Lines: 21 On 04/07/2017 17:58, Bjorn Helgaas wrote: > It's definitely a hassle to support chips with different register > layouts. Your hardware guys are really making your life hard :) Now where did I put my foam bat... > If the chips are fundamentally different, i.e., if they *operate* > differently in addition to having a different register layout, you > could make two separate drivers. It's the exact same underlying IP. Revision 2 is only a bug fix rev. IIUC, some of the fixes lead to adding a register here, removing a register there... and I don't think the HW dev ever considered the pain of supporting both revs within a single driver. This dual support explains some of the peculiarities you noted in my submission. Regards.