linux-kernel - Re: [PATCH v3 4/9] PCI/VGA: Improve the default VGA device selection

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Date:   Mon, 24 Jul 2023 20:16:18 +0800
From:   suijingfeng <suijingfeng@...ngson.cn>
To:     Bjorn Helgaas <helgaas@...nel.org>,
        Sui Jingfeng <sui.jingfeng@...ux.dev>
Cc:     David Airlie <airlied@...il.com>, amd-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        intel-gfx@...ts.freedesktop.org, kvm@...r.kernel.org,
        linux-pci@...r.kernel.org, linux-fbdev@...r.kernel.org,
        Alex Deucher <alexander.deucher@....com>,
        Christian Konig <christian.koenig@....com>,
        Pan Xinhui <Xinhui.Pan@....com>,
        Daniel Vetter <daniel@...ll.ch>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        Ben Skeggs <bskeggs@...hat.com>,
        Karol Herbst <kherbst@...hat.com>,
        Lyude Paul <lyude@...hat.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Hawking Zhang <Hawking.Zhang@....com>,
        Mario Limonciello <mario.limonciello@....com>,
        Lijo Lazar <lijo.lazar@....com>,
        YiPeng Chai <YiPeng.Chai@....com>,
        Bokun Zhang <Bokun.Zhang@....com>,
        Likun Gao <Likun.Gao@....com>,
        Ville Syrjala <ville.syrjala@...ux.intel.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Kevin Tian <kevin.tian@...el.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Yishai Hadas <yishaih@...dia.com>,
        Abhishek Sahu <abhsahu@...dia.com>,
        Yi Liu <yi.l.liu@...el.com>,
        Jani Nikula <jani.nikula@...el.com>
Subject: Re: [PATCH v3 4/9] PCI/VGA: Improve the default VGA device selection

Hi,

On 2023/7/20 03:32, Bjorn Helgaas wrote:
>> 2) It does not take the PCI Bar may get relocated into consideration.
>> 3) It is not effective for the PCI device without a dedicated VRAM Bar.
>> 4) It is device-agnostic, thus it has to waste the effort to iterate all
>>     of the PCI Bar to find the VRAM aperture.
>> 5) It has invented lots of methods to determine which one is the default
>>     boot device, but this is still a policy because it doesn't give the
>>     user a choice to override.
> I don't think we need a list of*potential*  problems.  We need an
> example of the specific problem this will solve, i.e., what currently
> does not work?


This version do allow the arbitration service works on non-x86 arch,

which also allow me remove a arch-specific workaround.

I will give more detail at the next version.


But I want to provide one more drawback of vgaarb here:


(6) It does not works for non VGA-compatible PCI(e) display controllers.


Because, currently, vgaarb deal with PCI VGA compatible devices only.

See another my patch set [1] for more elaborate discussion.

It also ignore PCI_CLASS_NOT_DEFINED_VGA as Maciej puts it[2].

While my approach do not required the display controller to be 
VGA-compatible to enjoy the arbitration service.

What do you think then?


[1] https://patchwork.freedesktop.org/patch/546690/?series=120548&rev=1

[2] https://lkml.org/lkml/2023/6/18/315