linux-kernel - Re: [PATCH 2/6] PCI/VGA: Deal with PCI VGA compatible devices only

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Message-ID: <20230725214928.GA666846@bhelgaas>
Date:   Tue, 25 Jul 2023 16:49:28 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     suijingfeng <suijingfeng@...ngson.cn>
Cc:     Sui Jingfeng <sui.jingfeng@...ux.dev>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Maxime Ripard <mripard@...nel.org>,
        loongson-kernel@...ts.loongnix.cn, dri-devel@...ts.freedesktop.org,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Mario Limonciello <mario.limonciello@....com>
Subject: Re: [PATCH 2/6] PCI/VGA: Deal with PCI VGA compatible devices only

On Sat, Jul 22, 2023 at 04:11:07PM +0800, suijingfeng wrote:
> ...
> In the future, we may want to expand VGAARB to deal all PCI display class
> devices, with another patch.
> 
> if (pdev->class >> 16 == PCI_BASE_CLASS_DISPLAY)
> 
>          // accept
> 
> else
> 
>       // return immediately.
> 
> 
> Then, we will have a more good chance to clarify the programmer interface.

I would prefer not to expand vgaarb to deal with all display devices
unless they actually need the legacy resources like [pci 0xa0000-0xbffff].

But maybe the consumer of these interfaces relies on vgaarb even for
devices that don't need those resources?  If so, please mention
examples of where they depend on vgaarb.

I expect the vgaarb interfaces are used by things that need to emulate
the option ROM to initialize the device.  If the device has a
programming interface other than 0000 0000b, the option ROM should not
be using the [pci 0xa0000-0xbffff] resource, so vgaarb should not be
needed.

Bjorn