linux-kernel - Re: [PATCH v5 1/9] PCI: Add helper for checking if a PCI device is a display controller

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Message-ID: <d8c7c973-0285-4891-9b4a-c8e3d4f0d6b7@kernel.org>
Date: Thu, 26 Jun 2025 16:14:59 -0500
From: Mario Limonciello <superm1@...nel.org>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>,
 Alex Deucher <alexander.deucher@....com>,
 Christian König <christian.koenig@....com>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 Lukas Wunner <lukas@...ner.de>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Woodhouse <dwmw2@...radead.org>, Lu Baolu <baolu.lu@...ux.intel.com>,
 Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
 Robin Murphy <robin.murphy@....com>,
 Alex Williamson <alex.williamson@...hat.com>,
 Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>,
 "open list:DRM DRIVERS" <dri-devel@...ts.freedesktop.org>,
 open list <linux-kernel@...r.kernel.org>,
 "open list:INTEL IOMMU (VT-d)" <iommu@...ts.linux.dev>,
 "open list:PCI SUBSYSTEM" <linux-pci@...r.kernel.org>,
 "open list:VFIO DRIVER" <kvm@...r.kernel.org>,
 "open list:SOUND" <linux-sound@...r.kernel.org>,
 Daniel Dadap <ddadap@...dia.com>,
 Mario Limonciello <mario.limonciello@....com>,
 Simona Vetter <simona.vetter@...ll.ch>
Subject: Re: [PATCH v5 1/9] PCI: Add helper for checking if a PCI device is a
 display controller

On 6/26/2025 3:43 PM, Bjorn Helgaas wrote:
> On Tue, Jun 24, 2025 at 03:30:34PM -0500, Mario Limonciello wrote:
>> From: Mario Limonciello <mario.limonciello@....com>
>>
>> Several places in the kernel do class shifting to match whether a
>> PCI device is display class.  Introduce a helper for those places to
>> use.
>>
>> Reviewed-by: Daniel Dadap <ddadap@...dia.com>
>> Reviewed-by: Simona Vetter <simona.vetter@...ll.ch>
>> Signed-off-by: Mario Limonciello <mario.limonciello@....com>
> 
> Acked-by: Bjorn Helgaas <bhelgaas@...gle.com>
> 
> Not sure how this should be merged, let me know if you want me to do
> something with it.

Unless there is opposition I think it's best to take it through PCI.

It's a trivial change to most the other drivers.  If there is opposition 
I think there will need to be an immutable tag for the others to merge.

> 
>> ---
>>   include/linux/pci.h | 15 +++++++++++++++
>>   1 file changed, 15 insertions(+)
>>
>> diff --git a/include/linux/pci.h b/include/linux/pci.h
>> index 05e68f35f3923..e77754e43c629 100644
>> --- a/include/linux/pci.h
>> +++ b/include/linux/pci.h
>> @@ -744,6 +744,21 @@ static inline bool pci_is_vga(struct pci_dev *pdev)
>>   	return false;
>>   }
>>   
>> +/**
>> + * pci_is_display - Check if a PCI device is a display controller
>> + * @pdev: Pointer to the PCI device structure
>> + *
>> + * This function determines whether the given PCI device corresponds
>> + * to a display controller. Display controllers are typically used
>> + * for graphical output and are identified based on their class code.
>> + *
>> + * Return: true if the PCI device is a display controller, false otherwise.
>> + */
>> +static inline bool pci_is_display(struct pci_dev *pdev)
>> +{
>> +	return (pdev->class >> 16) == PCI_BASE_CLASS_DISPLAY;
>> +}
>> +
>>   #define for_each_pci_bridge(dev, bus)				\
>>   	list_for_each_entry(dev, &bus->devices, bus_list)	\
>>   		if (!pci_is_bridge(dev)) {} else
>> -- 
>> 2.43.0
>>