From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5CF1E242D7F; Mon, 21 Jul 2025 23:00:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753138815; cv=none; b=TmKYnL5z7R8yiY6dSJUHGBnqf/lx1euQjlltCKE8kHaawDhwVjQtXt0HMF7is7MW6D6cjNJzyZqZ5C3x5XHXaEC4u4u36oMpZ9C2gWagNQZApCqW1L6DWc6wwpT0dBcm3dKxlrcfGx2cyOw/xAVR0BTOJgbXkMVlWQU2MrkIocI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753138815; c=relaxed/simple; bh=SnHb5Ff2Sxs8l3uYD7IYErUPUDBONk0p5oJ0NjX4EOs=; h=Date:From:To:Cc:Subject:Message-ID:MIME-Version:Content-Type: Content-Disposition:In-Reply-To; b=s1I4U+G/9pd+cJpt/sHrYjNGSkQE+imAMzBHIJDwQCb5747to2+ZggiIf5MUHETPHVtu0oqf6PkJEzQ1ZlLSqHa6tJsxnJpaX3UYBwcN2xisY/C/iTSdO037XjGbIP0/zsePwgV+EI50p1gHjW+fdDy4obI3QYuzNb2ohZviS7s= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Y3/h5a43; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Y3/h5a43" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B47ADC4CEED; Mon, 21 Jul 2025 23:00:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1753138814; bh=SnHb5Ff2Sxs8l3uYD7IYErUPUDBONk0p5oJ0NjX4EOs=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=Y3/h5a43DOytbrvY/BlcgPbSMxWUB93+MZtw+hgxr0Imk3Lm4UBoCF5wPCnSH+91C Xasgl3FtnWEB0ajbTTPnoxXchSdPm+ZiC5yhv2oFrr3MWTfbU3peH+EbNRQkC6rawc +/p3ygrqSZ86w0UJS3eZ0NkdoPPmdpiCenB+WbQWxh5n/SgMtXx8y0e9Za0PIKcc4x gOnUwYkBZappo9o59gUPFNzB9zoUK22nmMZAxkvE3ygWgfT8hirYcVGihGaX4sJThI HdMhfeLwpibSU83+rDUDmWk0M4Lh6h67rag2NDwbE/1tylJAk9Zl2WEsp5cSKqRUk7 vf1DiAByuE14w== Date: Mon, 21 Jul 2025 18:00:13 -0500 From: Bjorn Helgaas To: Mario Limonciello Cc: David Airlie , Bjorn Helgaas , Alex Deucher , Christian =?utf-8?B?S8O2bmln?= , Simona Vetter , Lukas Wunner , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Woodhouse , Lu Baolu , Joerg Roedel , Will Deacon , Robin Murphy , Alex Williamson , Jaroslav Kysela , Takashi Iwai , "open list:DRM DRIVERS" , open list , "open list:INTEL IOMMU (VT-d)" , "open list:PCI SUBSYSTEM" , "open list:VFIO DRIVER" , "open list:SOUND" , Daniel Dadap , Mario Limonciello Subject: Re: [PATCH v9 9/9] PCI: Add a new 'boot_display' attribute Message-ID: <20250721230013.GA2759370@bhelgaas> Precedence: bulk X-Mailing-List: linux-pci@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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: > > > > On Thu, Jul 17, 2025 at 12:38:12PM -0500, Mario Limonciello wrote: > > > > > From: Mario Limonciello > > > > > > > > > > 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 > > > > > +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. > > > > > > 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. Which loop are you referring to that walks through all the PCI devices? I see this: efifb_set_system for_each_pci_dev(dev) but that only looks at VGA devices and IIUC you also want to look at non-VGA GPUs. I don't see a loop in *this* series, where the screen_info path looks like this: pci_create_boot_display_file video_is_primary_device screen_info_pci_dev # added by "fbcon: Use screen info to find primary device" screen_info_resources __screen_info_pci_dev and we're basically matching the screen_info base/address with BAR values. The usual problem is that BARs may not have been assigned by the time pci_device_add() -> device_add() creates the static attributes. So we call pci_assign_unassigned_root_bus_resources() to assign all the BARs. Then we call pci_create_sysfs_dev_files(), where pci_create_resource_files() creates a "resource%d" file for each BAR. But since we're trying to find the GPU that was used by BIOS, I assume its BARs were programmed by BIOS and we shouldn't have to wait until after pci_assign_unassigned_root_bus_resources(). Bjorn