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 X-Spam-Level: X-Spam-Status: No, score=-4.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3792CC43461 for ; Thu, 10 Sep 2020 21:37:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EF1DB221E2 for ; Thu, 10 Sep 2020 21:37:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1599773867; bh=qJqfgEjM1JHkm7fFx5w2wAwPbg8pDBoa1SA0YP/hTRw=; h=Date:From:To:Cc:Subject:In-Reply-To:List-ID:From; b=cBvwHsFLMUtTYE8pZ7ErdPli6meWIige2fA5UGfmPcnnQ1eAmnNx19yarxeFxqboZ x9dg6JfVs7GEc+AUeCYSXnk9cJ3Yxf5J87m7dUErlX7cuCpyjyjC4goRGd6vhmtGY6 q1PykLUlAVDgkKyOlSpgCDyqb8ymMUoJ0yajan5M= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726872AbgIJVhl (ORCPT ); Thu, 10 Sep 2020 17:37:41 -0400 Received: from mail.kernel.org ([198.145.29.99]:49328 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730717AbgIJNdY (ORCPT ); Thu, 10 Sep 2020 09:33:24 -0400 Received: from localhost (52.sub-72-107-123.myvzw.com [72.107.123.52]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id E553C20809; Thu, 10 Sep 2020 13:31:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1599744717; bh=qJqfgEjM1JHkm7fFx5w2wAwPbg8pDBoa1SA0YP/hTRw=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=G+knM3WxDFUjRMS6LVKoufrc8iZ7RkD3+M3b6Iob39UGeFuC0yx1StLvAZSXrk3eE 90m2/vrAEnLx+FvxIKkDDAOt8feCA2zXVZg7Cv/lO2RBnkYBvDz72xi2x1C2HRBRVn VR4cjlxWJ8K2MwKk8up580rEFdZa64hoWb+OzyP4= Date: Thu, 10 Sep 2020 08:31:55 -0500 From: Bjorn Helgaas To: Jim Quinlan Cc: "open list:PCI NATIVE HOST BRIDGE AND ENDPOINT DRIVERS" , "maintainer:BROADCOM BCM7XXX ARM ARCHITECTURE" , Bjorn Helgaas , open list Subject: Re: [RESEND PATCH v1] PCI: pcie_bus_config can be set at build time Message-ID: <20200910133155.GA782074@bjorn-Precision-5520> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-pci-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On Thu, Sep 10, 2020 at 08:57:10AM -0400, Jim Quinlan wrote: > Hi Bjorn, > > On Wed, Sep 9, 2020 at 10:25 PM Bjorn Helgaas wrote: > > > > On Tue, Sep 08, 2020 at 12:32:48PM -0400, Jim Quinlan wrote: > > > The Kconfig is modified so that the pcie_bus_config setting can be done at > > > build time in the same manner as the CONFIG_PCIEASPM_XXXX choice. The > > > pci_bus_config setting may still be overridden by the bootline param. > > > > I guess... I really hate these build-time config settings for both > > ASPM and MPS/MRRS. But Linux just isn't smart or flexible enough to > > do the right thing at run-time, so I guess we're kind of stuck. > > > > I guess you have systems where you need a different default? > > Yes, we've been shipping our kernel with the DEFAULT and since we do > not have FW it is not configured optimally. Some customers have > noticed and I tell them to put 'pci=pcie_bus_safe' on their bootline > but I'd rather have this setting work for all customers as it yields > the option we want. I'm guessing you probably don't have any hotplug slots. Seems like we ought to be able to recognize that and pick pcie_bus_safe automatically. Someday. Maybe that's part of the description: if you have a closed system with no possibility of adding new devices, we can use the largest MPS that's supported by all devices, i.e., pcie_bus_safe. > > It'd be nice if we could put a little more detail in the Kconfig to > > help users choose the correct one. "Ensure MPS matches upstream > > bridge" is *accurate*, but it doesn't really tell me why I would > > choose this rather than a different one. > > IIRC I just copied the comments that were in the bootline settings. > I'm concerned about there being the same comment in two places; sooner > or later someone will update one place and not the other. True. It'd be nice if we at least had *one* place with a useful description. I don't think we have any today. Bjorn