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

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Date:   Tue, 1 Feb 2022 16:46:33 +0100
From:   Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
To:     Bjorn Helgaas <helgaas@...nel.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>
Cc:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Xuefeng Li <lixuefeng@...ngson.cn>,
        Huacai Chen <chenhuacai@...ngson.cn>
Subject: Re: [PATCH v8 00/10] vgaarb: Rework default VGA device selection

Hey,
 
Op 31-01-2022 om 23:23 schreef Bjorn Helgaas:
> [+to Maarten, Maxime, Thomas; beginning of thread:
> https://lore.kernel.org/r/20220106000658.243509-1-helgaas@kernel.org]
>
> 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.
> Where are we at with this series?  Is there anything I can do to move
> it forward?
>
> Bjorn

Hi Bjorn,


I'm afraid that I don't understand the vga arbiter or the vga code well enough to review.

Could you perhaps find someone who could review?

I see Chen wrote some patches and tested, so perhaps they could?

~Maarten

>> 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
>>