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=-6.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED 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 B6D58C4743D for ; Fri, 4 Jun 2021 19:56:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9895E613E4 for ; Fri, 4 Jun 2021 19:56:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230297AbhFDT6f (ORCPT ); Fri, 4 Jun 2021 15:58:35 -0400 Received: from mail.kernel.org ([198.145.29.99]:47728 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229854AbhFDT6e (ORCPT ); Fri, 4 Jun 2021 15:58:34 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 68F7F613EA; Fri, 4 Jun 2021 19:56:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1622836607; bh=AFpjjiA99h0nt4kcs5wc/Q6hDKnPZPZchEi3dNIHl9U=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=IEGObJaYdVHGM3hMxpDIBzCL7QUfZbpGqzGMgMaCg1NFWMTq+wZsTW8b+lvq7zIbi 7A95NF9c6OGnid9mt4NR45qJUAFOBjchGRVyg2yVDD6zzt8BQEk+HSlW6iDr08P2wI XY+AM9Pca+6xWnkddlv6L/p9zNn/Q7h9fcKiA+TIaHDjfAqsRhlgypM46yBUNhipVN Z/uSxdZOLx+bigF78FS01uKVUNjmqclyGU20vjEmoOgqWZQrpJULJ8LH/1lUaXMc8r wygraoTn9dXHDeUON02TEE6+czyAjA4ehQBuXlu6/Ygi6lGNGANVYJzJGKE1n+s0DP 3dwpbgbdTM4Uw== Date: Fri, 4 Jun 2021 14:56:46 -0500 From: Bjorn Helgaas To: Huacai Chen Cc: Bjorn Helgaas , Daniel Vetter , Greg KH , David Airlie , Maling list - DRI developers , Xuefeng Li , Huacai Chen , Linux PCI Subject: Re: [PATCH] vgaarb: Call vga_arb_device_init() after PCI enumeration Message-ID: <20210604195646.GA2231573@bjorn-Precision-5520> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On Fri, Jun 04, 2021 at 12:50:03PM +0800, Huacai Chen wrote: > On Thu, Jun 3, 2021 at 2:31 AM Bjorn Helgaas wrote: > > > > [+cc linux-pci] > > > > On Wed, Jun 2, 2021 at 11:22 AM Daniel Vetter wrote: > > > On Wed, Jun 02, 2021 at 06:36:03PM +0800, Huacai Chen wrote: > > > > On Wed, Jun 2, 2021 at 2:03 AM Daniel Vetter wrote: > > > > > On Tue, Jun 01, 2021 at 07:12:27PM +0200, Greg KH wrote: > > > > > > On Tue, Jun 01, 2021 at 05:56:40PM +0200, Daniel Vetter wrote: > > > > > > > On Fri, May 28, 2021 at 04:26:07PM +0800, Huacai Chen wrote: > > > > > > > > We should call vga_arb_device_init() after PCI enumeration, otherwise it > > > > > > > > may fail to select the default VGA device. Since vga_arb_device_init() > > > > > > > > and PCI enumeration function (i.e., pcibios_init() or acpi_init()) are > > > > > > > > both wrapped by subsys_initcall(), their sequence is not assured. So, we > > > > > > > > use subsys_initcall_sync() instead of subsys_initcall() to wrap vga_arb_ > > > > > > > > device_init(). > > > > > > > > > > > > Trying to juggle levels like this always fails if you build the code as > > > > > > a module. > > > > > > > > > > > > Why not fix it properly and handle the out-of-order loading by returning > > > > > > a "deferred" error if you do not have your resources yet? > > > > > > > > > > It's not a driver, it's kinda a bolted-on-the-side subsytem of pci. So not > > > > > something you can -EPROBE_DEFER I think, without potentially upsetting the > > > > > drivers that need this. > > > > > > > > > > Which might mean we should move this into pci subsystem proper perhaps? > > > > > Then adding the init call at the right time becomes trivial since we just > > > > > plug it in at the end of pci init. > > > > > > > > > > Also maybe that's how distros avoid this pain, pci is built-in, vgaarb is > > > > > generally a module, problem solved. > > > > > > > > > > Bjorn, would you take this entire vgaarb.c thing? From a quick look I > > > > > don't think it has a drm-ism in it (unlike vga_switcheroo, but that works > > > > > a bit differently and doesn't have this init order issue). > > > > Emmm, this patch cannot handle the hotplug case and module case, it > > > > just handles the case that vgaarb, drm driver and pci all built-in. > > > > But I think this is enough, because the original problem only happens > > > > on very few BMC-based VGA cards (BMC doesn't set the VGA Enable bit on > > > > the bridge, which breaks vgaarb). > > > > > > I'm not talking aout hotplug, just ordering the various pieces correctly. > > > That vgaarb isn't really a driver and also can't really handle hotplug is > > > my point. I guess that got lost a bit? > > > > > > Anyway my proposal is essentially to do a > > > > > > $ git move drivers/gpu/vga/vgaarb.c drivers/pci > > > > > > But I just realized that vgaarb is a bool option, so module isn't possible > > > anyway, and we could fix this by calling vgaarb from pcibios init (with an > > > empty static inline in the header if vgaarb is disabled). That makes the > > > dependency very explicit and guarantees it works correctly. > > > > pcibios_init() is also an initcall and is implemented by every arch. > > I agree that calling vga_arb_device_init() directly from > > pcibios_init() would probably fix this problem, and it would be really > > nice to have it not be an initcall. But it's also kind of a pain to > > have to update all those copies of pcibios_init(), and I would be > > looking for a way to unify it since it's not really an arch-specific > > thing. > > > > I think the simplest solution, which I suggested earlier [1], would be > > to explicitly call vga_arbiter_add_pci_device() directly from the PCI > > core when it enumerates a VGA device. Then there's no initcall and no > > need for the BUS_NOTIFY_ADD/DEL_DEVICE stuff. > > vga_arbiter_add_pci_device() could set the default VGA device when it > > is enumerated, and change the default device if we enumerate a > > "better" one. And hotplug VGA devices would work automatically. > Emm, It seems that your solution has some difficulties to remove the > whole initcall(vga_arb_device_init): we call > vga_arbiter_add_pci_device() in pci_bus_add_device(), the > list_for_each_entry() loop can be moved to > vga_arbiter_check_bridge_sharing(), vga_arb_select_default_device() > can be renamed to vga_arb_update_default_device() and be called in > vga_arbiter_add_pci_device(), but how to handle > misc_register(&vga_arb_device)? Might need to keep vga_arb_device_init() as an initcall, but remove everything from it except the misc_register().