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Date:   Mon, 24 Jul 2023 20:16:18 +0800
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Subject: Re: [PATCH v3 4/9] PCI/VGA: Improve the default VGA device selection
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To:     Bjorn Helgaas <helgaas@kernel.org>,
        Sui Jingfeng <sui.jingfeng@linux.dev>
Cc:     David Airlie <airlied@gmail.com>, amd-gfx@lists.freedesktop.org,
        dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
        intel-gfx@lists.freedesktop.org, kvm@vger.kernel.org,
        linux-pci@vger.kernel.org, linux-fbdev@vger.kernel.org,
        Alex Deucher <alexander.deucher@amd.com>,
        Christian Konig <christian.koenig@amd.com>,
        Pan Xinhui <Xinhui.Pan@amd.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        Jani Nikula <jani.nikula@linux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@intel.com>,
        Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>,
        Ben Skeggs <bskeggs@redhat.com>,
        Karol Herbst <kherbst@redhat.com>,
        Lyude Paul <lyude@redhat.com>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Alex Williamson <alex.williamson@redhat.com>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <mripard@kernel.org>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        Hawking Zhang <Hawking.Zhang@amd.com>,
        Mario Limonciello <mario.limonciello@amd.com>,
        Lijo Lazar <lijo.lazar@amd.com>,
        YiPeng Chai <YiPeng.Chai@amd.com>,
        Bokun Zhang <Bokun.Zhang@amd.com>,
        Likun Gao <Likun.Gao@amd.com>,
        Ville Syrjala <ville.syrjala@linux.intel.com>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        Kevin Tian <kevin.tian@intel.com>,
        Cornelia Huck <cohuck@redhat.com>,
        Yishai Hadas <yishaih@nvidia.com>,
        Abhishek Sahu <abhsahu@nvidia.com>,
        Yi Liu <yi.l.liu@intel.com>,
        Jani Nikula <jani.nikula@intel.com>
References: <20230719193233.GA511659@bhelgaas>
From:   suijingfeng <suijingfeng@loongson.cn>
In-Reply-To: <20230719193233.GA511659@bhelgaas>
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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