linux-kernel - Re: [PATCH 2/4] PCI/VGA: Deal only with PCI VGA class devices

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Message-ID: <20230719180752.GA509850@bhelgaas>
Date:   Wed, 19 Jul 2023 13:07:52 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Sui Jingfeng <sui.jingfeng@...ux.dev>
Cc:     Sui Jingfeng <suijingfeng@...ngson.cn>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Maxime Ripard <mripard@...nel.org>,
        dri-devel@...ts.freedesktop.org,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Mario Limonciello <mario.limonciello@....com>
Subject: Re: [PATCH 2/4] PCI/VGA: Deal only with PCI VGA class devices

On Tue, Jul 18, 2023 at 06:14:00PM -0500, Bjorn Helgaas wrote:
> On Fri, Jun 30, 2023 at 06:17:29PM +0800, Sui Jingfeng wrote:
> > From: Sui Jingfeng <suijingfeng@...ngson.cn>
> > 
> > VGAARB should only care about PCI VGA class devices (pdev->class == 0x0300)
> > since only those devices might have VGA routed to them.
> 
> This is not actually a question of whether VGA addresses (mem
> 0xa0000-0xbffff and io 0x3b0-0x3bb, 0x3c0-0x3df) might be *routed* to
> the device because that routing is controlled by the bridge VGA Enable
> bit, not by a device Class Code.
> 
> I think the important question here is what devices will *respond* to
> those VGA addresses.  The VGA arbiter works by managing bridge VGA
> Enable bits, so if we know a device doesn't respond to the VGA
> addresses, there's no point in adding a vga_device for it.

Sorry, I see that I replied to an old version of this patch.  I'll go
look at this series instead:

https://lore.kernel.org/r/20230711134354.755966-1-sui.jingfeng@linux.dev

Bjorn