linux-kernel - Re: [PATCH v9 9/9] PCI: Add a new 'boot

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Message-ID: <20250718172545.GA2703510@bhelgaas>
Date: Fri, 18 Jul 2025 12:25:45 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Mario Limonciello <superm1@...nel.org>
Cc: David Airlie <airlied@...il.com>, Bjorn Helgaas <bhelgaas@...gle.com>,
	Alex Deucher <alexander.deucher@....com>,
	Christian König <christian.koenig@....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>
Subject: Re: [PATCH v9 9/9] PCI: Add a new 'boot_display' attribute

On Thu, Jul 17, 2025 at 12:38:12PM -0500, Mario Limonciello wrote:
> From: Mario Limonciello <mario.limonciello@....com>
> 
> On systems with multiple GPUs there can be uncertainty which GPU is the
> primary one used to drive the display at bootup. In some desktop
> environments this can lead to increased power consumption because
> secondary GPUs may be used for rendering and never go to a low power
> state. In order to disambiguate this add a new sysfs attribute
> 'boot_display' that uses the output of video_is_primary_device() to
> populate whether a PCI device was used for driving the display.

> +What:		/sys/bus/pci/devices/.../boot_display
> +Date:		October 2025
> +Contact:	Linux PCI developers <linux-pci@...r.kernel.org>
> +Description:
> +		This file indicates that displays connected to the device were
> +		used to display the boot sequence.  If a display connected to
> +		the device was used to display the boot sequence the file will
> +		be present and contain "1".

>  int __must_check pci_create_sysfs_dev_files(struct pci_dev *pdev)
>  {
> +	int retval;
> +
>  	if (!sysfs_initialized)
>  		return -EACCES;
>  
> +	retval = pci_create_boot_display_file(pdev);

In addition to Mani's question about whether /sys/bus/pci/ is the
right place for this (which is a very good question), it's also been
pointed out to me that we've been trying to get rid of
pci_create_sysfs_dev_files() for years.

If it's possible to make this a static attribute that would be much,
much cleaner.

> +	if (retval)
> +		return retval;
> +
>  	return pci_create_resource_files(pdev);
>  }
>  
> @@ -1671,6 +1716,7 @@ void pci_remove_sysfs_dev_files(struct pci_dev *pdev)
>  	if (!sysfs_initialized)
>  		return;
>  
> +	pci_remove_boot_display_file(pdev);
>  	pci_remove_resource_files(pdev);
>  }
>  
> -- 
> 2.43.0
>