linux-kernel - Re: [-next 4/5] drm/virgpu: Switch to pci_is

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Date:   Fri, 6 Oct 2023 19:22:42 +0800
From:   Sui Jingfeng <suijingfeng@...ngson.cn>
To:     Bjorn Helgaas <helgaas@...nel.org>,
        Sui Jingfeng <sui.jingfeng@...ux.dev>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Gerd Hoffmann <kraxel@...hat.com>,
        Gurchetan Singh <gurchetansingh@...omium.org>,
        Chia-I Wu <olvaffe@...il.com>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        virtualization@...ts.linux-foundation.org,
        David Airlie <airlied@...hat.com>
Subject: Re: [-next 4/5] drm/virgpu: Switch to pci_is_vga()

Hi,


On 2023/10/6 05:57, Bjorn Helgaas wrote:
> In subject: "drm/virtio" to match previous history.
>
> On Wed, Aug 30, 2023 at 07:15:31PM +0800, Sui Jingfeng wrote:
>> From: Sui Jingfeng <suijingfeng@...ngson.cn>
>>
>> Should be no functional change, just for cleanup purpose.
>>
>> Cc: David Airlie <airlied@...hat.com>
>> Cc: Gerd Hoffmann <kraxel@...hat.com>
>> Cc: Gurchetan Singh <gurchetansingh@...omium.org>
>> Cc: Chia-I Wu <olvaffe@...il.com>
>> Cc: Daniel Vetter <daniel@...ll.ch>
>> Signed-off-by: Sui Jingfeng <suijingfeng@...ngson.cn>
>> ---
>>   drivers/gpu/drm/virtio/virtgpu_drv.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/virtio/virtgpu_drv.c b/drivers/gpu/drm/virtio/virtgpu_drv.c
>> index add075681e18..3a368304475a 100644
>> --- a/drivers/gpu/drm/virtio/virtgpu_drv.c
>> +++ b/drivers/gpu/drm/virtio/virtgpu_drv.c
>> @@ -51,7 +51,7 @@ static int virtio_gpu_pci_quirk(struct drm_device *dev)
>>   {
>>   	struct pci_dev *pdev = to_pci_dev(dev->dev);
>>   	const char *pname = dev_name(&pdev->dev);
>> -	bool vga = (pdev->class >> 8) == PCI_CLASS_DISPLAY_VGA;
>> +	bool vga = pci_is_vga(pdev);
> This *is* a functional change: Previously "vga" was only true for
> PCI_CLASS_DISPLAY_VGA (0x0300).  Now it will be true for both
> PCI_CLASS_DISPLAY_VGA (0x0300) and PCI_CLASS_DISPLAY_OTHER (0x0380).
>
> Is that desirable?  I can't tell.  Maybe the GPU folks will chime in.
>

Yes, the vga variable still will be "true" for the PCI_CLASS_DISPLAY_VGA (0x0300) class code,
and this is the major case. But the devices with PCI_CLASS_NOT_DEFINED_VGA class code are quite
uncommon, and virtio gpu is virtual GPU driver, It is unlikely that the QEMU to emulate a
old device with PCI_CLASS_NOT_DEFINED_VGA class code. I means that there no reason to do so.
Am I correct? Is there anyone know more?

For virtio virtual GPU driver, I would like to drop this patch, if no one response.

We probably only need to consider PCI_CLASS_NOT_DEFINED_VGA case for the real (probably old) hardware device.
It do exists, as Maciej mention at [1].

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


>>   	int ret;
>>   
>>   	DRM_INFO("pci: %s detected at %s\n",
>> -- 
>> 2.34.1
>>