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 DF55F323D; Tue, 22 Jul 2025 00:28:23 +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=1753144104; cv=none; b=A++ewzS3VMBlGLKJhyIJVOTAeF3D+bBxcoBquBiWYIX2X4YhLJkbqavCcGq5B2639FEjrOToJag/oz3YKfiAy1cxB0l449/oZeXu1C6KcflshMfFQwwg2UxewB+JE9d+3OWycnXfPlKfPYxyzgyfZE1kGoxLCW8MLRKuLRa+qSg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753144104; c=relaxed/simple; bh=YgB7btUbdx74E1DahlEGqRapSpAUsvGQ9MXW1F6d/to=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Tgv37s4L0lf1gH3BY3Ch7eGbSIYv6TIlTbVaCjH154gCt4lM32VgMOxGCl92mOpDRCrt19UHl+4Jgj7r5LErLYv2CAsLgT8fTmR+n6MCVIucIzb0MFV4WG0ltvgDgVwIsjvgm8k7grsJPkVmpLYyp0vLkV1u5EXVfUoIKUB9ZuQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=oThxSnot; 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="oThxSnot" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9A439C4CEED; Tue, 22 Jul 2025 00:28:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1753144103; bh=YgB7btUbdx74E1DahlEGqRapSpAUsvGQ9MXW1F6d/to=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=oThxSnotz2JIQp0iby5oudEnvB1XD1JDPe0qt1tlygXywxJmjT4MUP+iJlcxEedGN 8a39OeK/QBWqhLjHzC9o6wAgpbIfq+/atg1iqIxckKssiyTsH0RFoUiJFp25DCPfFl 8bNu06QLkt8M9pPVJ1/f9IwRAxqojL6pcLGGz4s6uC1JF4Lsg/whH31YjF6rLP5NTY Ca8UEHnhtTL39hxmrfz5/GpOzrlxT4/VoG0KyvOi4J4dupJmESHKp+jHM1JOu0Ht3Y 4dS3jmxmT0tBAx7nJd98RiDvLCB3I8skpvc1ya16JMapDQat3C8DUzcLiR4w+nSkIG 5HQHHG6fzNavw== Message-ID: <860bcc59-f0d0-4c8d-865c-89127c213cdf@kernel.org> Date: Mon, 21 Jul 2025 19:28:07 -0500 Precedence: bulk X-Mailing-List: linux-pci@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v9 9/9] PCI: Add a new 'boot_display' attribute To: Bjorn Helgaas Cc: David Airlie , Bjorn Helgaas , Alex Deucher , =?UTF-8?Q?Christian_K=C3=B6nig?= , 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 References: <20250721230013.GA2759370@bhelgaas> Content-Language: en-US From: Mario Limonciello In-Reply-To: <20250721230013.GA2759370@bhelgaas> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 7/21/25 6:00 PM, Bjorn Helgaas wrote: > 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 Yes it was screen_info_pci_dev() and __screen_info_pci_dev(). The resources weren't ready on the first call into __screen_info_pci_dev(). That's why the attribute needed to be created later. But the sysfs group update or using DRM both avoid this problem and are totally fine alternatives.