linux-kernel - Re: [PATCH v7 2/8] PCI/VGA: Deal only with VGA class devices

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Date:   Mon, 19 Jun 2023 04:02:48 +0100 (BST)
From:   "Maciej W. Rozycki" <macro@...am.me.uk>
To:     Sui Jingfeng <15330273260@....cn>
cc:     Bjorn Helgaas <bhelgaas@...gle.com>, amd-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        intel-gfx@...ts.freedesktop.org, nouveau@...ts.freedesktop.org,
        linux-pci@...r.kernel.org, kvm@...r.kernel.org,
        linux-fbdev@...r.kernel.org, Sui Jingfeng <suijingfeng@...ngson.cn>
Subject: Re: [PATCH v7 2/8] PCI/VGA: Deal only with VGA class devices

On Tue, 13 Jun 2023, Sui Jingfeng wrote:

> Deal only with the VGA devcie(pdev->class == 0x0300), so replace the

 Typo here: s/devcie/device/.

> pci_get_subsys() function with pci_get_class(). Filter the non-PCI display
> device(pdev->class != 0x0300) out. There no need to process the non-display
> PCI device.

 I've only come across this patch series now.  Without diving into what 
this code actually does I have just one question as a matter of interest.

> diff --git a/drivers/pci/vgaarb.c b/drivers/pci/vgaarb.c
> index c1bc6c983932..22a505e877dc 100644
> --- a/drivers/pci/vgaarb.c
> +++ b/drivers/pci/vgaarb.c
> @@ -1500,7 +1496,9 @@ static int pci_notify(struct notifier_block *nb, unsigned long action,
>  	struct pci_dev *pdev = to_pci_dev(dev);
>  	bool notify = false;
>  
> -	vgaarb_dbg(dev, "%s\n", __func__);
> +	/* Only deal with VGA class devices */
> +	if (pdev->class != PCI_CLASS_DISPLAY_VGA << 8)
> +		return 0;

 Hmm, shouldn't this also handle PCI_CLASS_NOT_DEFINED_VGA?  As far as I 
know it is the equivalent of PCI_CLASS_DISPLAY_VGA for PCI <= 2.0 devices 
that were implemented before the idea of PCI device classes has developed 
into its current form.  I may have such a VGA device somewhere.

  Maciej