linux-kernel - Re: [PATCH v8 00/10] vgaarb: Rework default VGA device selection

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Message-ID: <20220106163035.GA292309@bhelgaas>
Date:   Thu, 6 Jan 2022 10:30:35 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     David Airlie <airlied@...ux.ie>, Daniel Vetter <daniel@...ll.ch>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>
Cc:     Xuefeng Li <lixuefeng@...ngson.cn>,
        Huacai Chen <chenhuacai@...il.com>,
        Huacai Chen <chenhuacai@...ngson.cn>,
        linux-pci@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>
Subject: Re: [PATCH v8 00/10] vgaarb: Rework default VGA device selection

[+to Maarten, Maxime, Thomas: sorry, I forgot to use
get_maintainer.pl so I missed you the first time.  Beginning of thread:
https://lore.kernel.org/all/20220106000658.243509-1-helgaas@kernel.org/#t
Git branch with this v8 + a couple trivial renames, based on v5.16-rc1:
https://git.kernel.org/pub/scm/linux/kernel/git/helgaas/pci.git/log/?h=0f4caffa1297]

On Wed, Jan 05, 2022 at 06:06:48PM -0600, Bjorn Helgaas wrote:
> From: Bjorn Helgaas <bhelgaas@...gle.com>
> 
> Current default VGA device selection fails in some cases because part of it
> is done in the vga_arb_device_init() subsys_initcall, and some arches
> enumerate PCI devices in pcibios_init(), which runs *after* that.
> 
> For example:
> 
>   - On BMC system, the AST2500 bridge [1a03:1150] does not implement
>     PCI_BRIDGE_CTL_VGA.  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 on MIPS system, they are enumerated by
>     pcibios_init(), which typically runs *after* vga_arb_device_init().
> 
> This series consolidates all the default VGA device selection in
> vga_arbiter_add_pci_device(), which is always called after enumerating a
> PCI device.
> 
> Almost all the work here is Huacai's.  I restructured it a little bit and
> added a few trivial patches on top.
> 
> I'd like to move vgaarb.c to drivers/pci eventually, but there's another
> initcall ordering snag that needs to be resolved first, so this leaves 
> it where it is.
> 
> Bjorn
> 
> Version history:
> V0 original implementation as final quirk to set default device.
> https://lore.kernel.org/r/20210514080025.1828197-6-chenhuacai@loongson.cn
> 
> V1 rework vgaarb to do all default device selection in
> vga_arbiter_add_pci_device().
> https://lore.kernel.org/r/20210705100503.1120643-1-chenhuacai@loongson.cn
> 
> V2 move arbiter to PCI subsystem, fix nits.
> https://lore.kernel.org/r/20210722212920.347118-1-helgaas@kernel.org
> 
> V3 rewrite the commit log of the last patch (which is also summarized
> by Bjorn).
> https://lore.kernel.org/r/20210820100832.663931-1-chenhuacai@loongson.cn
> 
> V4 split the last patch to two steps.
> https://lore.kernel.org/r/20210827083129.2781420-1-chenhuacai@loongson.cn
> 
> V5 split Patch-9 again and sort the patches.
> https://lore.kernel.org/r/20210911093056.1555274-1-chenhuacai@loongson.cn
> 
> V6 split Patch-5 again and sort the patches again.
> https://lore.kernel.org/r/20210916082941.3421838-1-chenhuacai@loongson.cn
> 
> V7 stop moving vgaarb to drivers/pci because of ordering issues with
> misc_init().
> https://lore.kernel.org/r/20211015061512.2941859-1-chenhuacai@loongson.cn
> https://lore.kernel.org/r/CAAhV-H7FhAjM-Ha42Z1dLrE4PvC9frfyeU27KHWcyWKkMftEsA@mail.gmail.com
> 
> 
> Bjorn Helgaas (8):
>   vgaarb: Factor out vga_select_framebuffer_device()
>   vgaarb: Factor out default VGA device selection
>   vgaarb: Move framebuffer detection to ADD_DEVICE path
>   vgaarb: Move non-legacy VGA detection to ADD_DEVICE path
>   vgaarb: Move disabled VGA device detection to ADD_DEVICE path
>   vgaarb: Remove empty vga_arb_device_card_gone()
>   vgaarb: Use unsigned format string to print lock counts
>   vgaarb: Replace full MIT license text with SPDX identifier
> 
> Huacai Chen (2):
>   vgaarb: Move vga_arb_integrated_gpu() earlier in file
>   vgaarb: Log bridge control messages when adding devices
> 
>  drivers/gpu/vga/vgaarb.c | 311 +++++++++++++++++++--------------------
>  1 file changed, 154 insertions(+), 157 deletions(-)
> 
> -- 
> 2.25.1
> 
>