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=-6.7 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 EBDE1C4338F for ; Thu, 19 Aug 2021 21:52:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CFB9B6023E for ; Thu, 19 Aug 2021 21:52:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235676AbhHSVxT (ORCPT ); Thu, 19 Aug 2021 17:53:19 -0400 Received: from mail.kernel.org ([198.145.29.99]:35110 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233567AbhHSVxT (ORCPT ); Thu, 19 Aug 2021 17:53:19 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 16DA661029; Thu, 19 Aug 2021 21:52:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1629409962; bh=lVxMSHjueZlMfEBoUSerhjw3+tnhPwfYJwK4Bjj66FE=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=U5X0Iox8zg+g4AdUXxKc66LA0Ku4gfX4YtZXt8g0KcL1qPsxVaXnc1oRXTm9Sm+Aj 9oMnyecskuAJgQtaKLbpj5C8C23tXWjlF/q8hQpZEiCxHicpOq9IBTIGaSZwWq7Tu6 W7AEHT6IWUcDyxvbrXz/SfPxuE5SBGY55wnwTIaTHiwAxOMlzCJh4WTlnMasPJLK2H WvEhKG9CPEsYvzMNL6aa9D0bg5v6xqkp4JH8C8AUkK0eLo3LFVCMcBp4eyMKPJto70 N/FAp6hRtvWinx99Uf8sCTFxPot4aIyB87TfXypFUJ4hx9h7Rc1Q1memGl26W67BIt L418Cy9FD+8gQ== Date: Thu, 19 Aug 2021 16:52:40 -0500 From: Bjorn Helgaas To: Huacai Chen Cc: Huacai Chen , David Airlie , Maling list - DRI developers , linux-pci , Bjorn Helgaas , Xuefeng Li , Christoph Hellwig , Daniel Vetter Subject: Re: [PATCH v2 0/9] PCI/VGA: Rework default VGA device selection Message-ID: <20210819215240.GA3241693@bjorn-Precision-5520> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210809185901.GA2176971@bjorn-Precision-5520> Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On Mon, Aug 09, 2021 at 01:59:01PM -0500, Bjorn Helgaas wrote: > On Tue, Aug 03, 2021 at 12:06:44PM -0500, Bjorn Helgaas wrote: > > On Sat, Jul 24, 2021 at 05:30:02PM +0800, Huacai Chen wrote: > > > On Sat, Jul 24, 2021 at 8:10 AM Bjorn Helgaas wrote: > > > > Thanks for the above; that was helpful. To summarize: > > > > > > > > - On your system, the AST2500 bridge [1a03:1150] does not implement > > > > PCI_BRIDGE_CTL_VGA [1]. This is perfectly legal but means the > > > > legacy VGA resources won't reach downstream devices unless they're > > > > included in the usual bridge windows. > > > > > > > > - vga_arb_select_default_device() will set a device below such a > > > > bridge as the default VGA device as long as it has PCI_COMMAND_IO > > > > and PCI_COMMAND_MEMORY enabled. > > > > > > > > - vga_arbiter_add_pci_device() is called for every VGA device, > > > > either at boot-time or at hot-add time, and it will also set the > > > > device as the default VGA device, but ONLY if all bridges leading > > > > to it implement PCI_BRIDGE_CTL_VGA. > > > > > > > > - This difference between vga_arb_select_default_device() and > > > > vga_arbiter_add_pci_device() means that a device below an AST2500 > > > > or similar bridge can only be set as the default if it is > > > > enumerated before vga_arb_device_init(). > > > > > > > > - On ACPI-based systems, PCI devices are enumerated by acpi_init(), > > > > which runs before vga_arb_device_init(). > > > > > > > > - On non-ACPI systems, like your MIPS system, they are enumerated by > > > > pcibios_init(), which typically runs *after* > > > > vga_arb_device_init(). > > > > > > > > So I think the critical change is actually that you made > > > > vga_arb_update_default_device(), which you call from > > > > vga_arbiter_add_pci_device(), set the default device even if it does > > > > not own the VGA resources because an upstream bridge doesn't implement > > > > PCI_BRIDGE_CTL_VGA, i.e., > > > > > > > > (vgadev->owns & VGA_RSRC_LEGACY_MASK) != VGA_RSRC_LEGACY_MASK > > > > > > > > Does that seem right? > > > > > > Yes, that's right. > > > > I think that means I screwed up. I somehow had it in my head that the > > hot-add path would never set the default VGA device. But that is > > false. > > > > I still think we should move vgaarb.c to drivers/pci/ and get it more > > tightly integrated into the PCI core. > > > > BUT that's a lot of churn and obscures the simple change that fixes > > the problem for you. So I think the first step should be the change > > to vga_arb_update_default_device() so it sets the default device even > > when the upstream bridge doesn't implement PCI_BRIDGE_CTL_VGA. > > > > That should be a relatively small change, and I think it's better to > > make the fix before embarking on major restructuring. > > To make sure this doesn't get lost: I'm hoping you can separate out > and post the small patch to vga_arb_update_default_device(). > > I can look at the move/restructure stuff later. What's happening with this? I'm still assuming you can post a small patch to vga_arb_update_default_device() that's suitable for v5.15, Huacai. Otherwise I'm afraid we won't make any forward progress this cycle. Bjorn