Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751922AbdF3RQS (ORCPT ); Fri, 30 Jun 2017 13:16:18 -0400 Received: from mail-it0-f52.google.com ([209.85.214.52]:34861 "EHLO mail-it0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751072AbdF3RQQ (ORCPT ); Fri, 30 Jun 2017 13:16:16 -0400 MIME-Version: 1.0 In-Reply-To: References: <20170316215057.452220163@linutronix.de> <20170630031849.GP23705@tassilo.jf.intel.com> From: Linus Torvalds Date: Fri, 30 Jun 2017 10:16:15 -0700 X-Google-Sender-Auth: GVDTXcETNPtpXyIqMhC5nGtWIZw Message-ID: Subject: Re: [tip:x86/platform] x86/PCI/mmcfg: Switch to ECAM config mode if possible To: Thomas Gleixner Cc: Andi Kleen , Yinghai Lu , Stephane Eranian , "H. Peter Anvin" , Ingo Molnar , Peter Zijlstra , Borislav Petkov , Linux Kernel Mailing List , Bjorn Helgaas , Matthew Wilcox , Ivan Kokshaysky , "linux-tip-commits@vger.kernel.org" Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1304 Lines: 38 On Fri, Jun 30, 2017 at 7:30 AM, Thomas Gleixner wrote: >> But MCFG problems were a long time ago and noone uses these systems anymore, >> so perhaps he is right. > > The obvious solution to this is to force type 1 for older machines, i.e. <= > K8. Some day we should stop supporting 15+ years old crap just because we > can. No. The fact is, type 1 is the *good* thing. It's the standard thing that has worked pretty much forever, and that is not just tested, but has good semantics. The new stuff is the crazy crap. It's crazy crap in so many ways: - non-deterministic memory addresses found in firmware tables that have had bugs - using MMIO means that there are lots of basic issues with fundamental things like write gathering and ordering The right thing to do is to just admit that the extended mmcfg isn't actually the rigth thjing to do by default, and only use it when you have to. "Newer" does not always mean "better", and there's been lots of bad hardware (and bad firmware). So use the "enhanced" one for stuff above the 256-byte limit. Not for basic probing. Anmd don't think that it should be phased out just because it's old. Old is often *good*. Old means stable. Old means tested. Old means simple. Those are all *good* thing. Linus