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

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Message-ID: <aHyHJZwIgEya_yfn@wunner.de>
Date: Sun, 20 Jul 2025 08:05:25 +0200
From: Lukas Wunner <lukas@...ner.de>
To: Mario Limonciello <superm1@...nel.org>
Cc: Bjorn Helgaas <helgaas@...nel.org>, David Airlie <airlied@...il.com>,
	Alex Deucher <alexander.deucher@....com>,
	Christian König <christian.koenig@....com>,
	Simona Vetter <simona@...ll.ch>,
	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>
Subject: Re: [PATCH v9 9/9] PCI: Add a new 'boot_display' attribute

On Fri, Jul 18, 2025 at 12:44:11PM -0500, Mario Limonciello wrote:
> On 7/18/2025 12:36 PM, Bjorn Helgaas wrote:
> > On Fri, Jul 18, 2025 at 12:29:05PM -0500, Mario Limonciello wrote:
> > > On 7/18/2025 12:25 PM, Bjorn Helgaas wrote:
> > > > 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.
> > > 
> > > Right - I tried to do this, but the problem is at the time the PCI device is
> > > created the information needed to make the judgement isn't ready.  The
> > > options end up being:
> > > * a sysfs file for every display device with 0/1
> > > * a sysfs file that is not accurate until later in the boot
> > 
> > What's missing?  The specifics might be helpful if someone has another
> > crack at getting rid of pci_create_sysfs_dev_files() in the future.
> 
> The underlying SCREEN_INFO code tries to walk through all the PCI devices in
> a loop, but at the time all the devices are walked the memory regions
> associated with the device weren't populated.
> 
> So my earlier hack was to re-run the screen info check, and it was awful.

Well have you explored the sysfs_update_group() approach you mentioned
earlier?

https://lore.kernel.org/r/5cc01163-1feb-4a18-8060-27f4da39b2e4@kernel.org/

Thanks,

Lukas