linux-kernel - Re: [PATCH v8 9/9] PCI: Add a new 'boot

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Message-ID: <20250716-upbeat-tody-of-psychology-93e2a2@houat>
Date: Wed, 16 Jul 2025 10:22:27 +0200
From: Maxime Ripard <mripard@...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>, 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 v8 9/9] PCI: Add a new 'boot_display' attribute

Hi Mario,

On Mon, Jul 14, 2025 at 04:21:46PM -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 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.
> 
> Reviewed-by: Thomas Zimmermann <tzimmermann@...e.de>
> Signed-off-by: Mario Limonciello <mario.limonciello@....com>
> ---
> v7:
>  * fix lkp failure
>  * Add tag
> v6:
>  * Only show for the device that is boot display
>  * Only create after PCI device sysfs files are initialized to ensure
>    that resources are ready.
> v4:
>  * new patch
> ---
>  Documentation/ABI/testing/sysfs-bus-pci |  8 +++++
>  drivers/pci/pci-sysfs.c                 | 46 +++++++++++++++++++++++++
>  2 files changed, 54 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-pci b/Documentation/ABI/testing/sysfs-bus-pci
> index 69f952fffec72..8b455b1a58852 100644
> --- a/Documentation/ABI/testing/sysfs-bus-pci
> +++ b/Documentation/ABI/testing/sysfs-bus-pci
> @@ -612,3 +612,11 @@ Description:
>  
>  		  # ls doe_features
>  		  0001:01        0001:02        doe_discovery
> +
> +What:		/sys/bus/pci/devices/.../boot_display
> +Date:		October 2025
> +Contact:	Linux PCI developers <linux-pci@...r.kernel.org>
> +Description:
> +		This file indicates the device was used as a boot
> +		display. If the device was used as the boot display, the file
> +		will be present and contain "1".

It would probably be a good idea to define what a "boot display" here
is. I get what you mean, but it's pretty vague and could easily be
misunderstood.

Maxime

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