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 37E7E1D7984; Thu, 26 Jun 2025 21:12:24 +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=1750972345; cv=none; b=N06qdniNT2jKBIra+4M2PPthSkVJ0cRYYqAHkT4ADSRuyoOHXTG++7iD+fkPEKCp4Ty1Rfs3L5DxWljKNmmCHon7dSpA67eFTPdiIY1d9k9kUiAiZdCzBtbZ87GqZqMFDe0X7gWhlQZhQLSDf73IkSPPD2jRDNOYNW7CPT0XqRo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750972345; c=relaxed/simple; bh=1HGJ3l6ikdw5NCSll50pAw9X5BjsMp1eQTlXjZQSkac=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=utohfPTG4d3AhTs/LEVwcbjvkRCxgTYqqos8tVE2Y6iw7jBczDKwam9opmlFt5c6NdfkVX6jfPIcnoAot7WWR/rnFW/unEG85ykl2tlSLUv2o7BBFb1UuRYQInAaDcz/sF+hd2MdURT9dQK5QH6AMpwDtJM9JMhzs185mscmWFA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=NdEtFuxl; 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="NdEtFuxl" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 432F4C4CEEB; Thu, 26 Jun 2025 21:12:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1750972344; bh=1HGJ3l6ikdw5NCSll50pAw9X5BjsMp1eQTlXjZQSkac=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=NdEtFuxltw0oevgdXEQ5cl0fDHM2QHdYqsqqW3HNosUK/GcSDLIPpUaM5kKYBHCV5 b7tRWS/EqxZHvlaO6XqF5zSrPTtNLxEIWaJh+oAyZNgT8or6xhUmXL2Omj456tIZ1u 71RnxnZ22zI0pGFx8RfNJWfrVuB60YkTbsiIxVXaJcj8U1QgUkql01/UNMQJtlH+vk 8A5sKrunL/G9C0wPJJ8FZxO4MKWXS9tQ2VG3UgHcglHz6MN+WHFIs8yGB9a076ccY4 79wJ9jH8bHDWhhzFflge/EV30PGMgQPDHu2TQlVLKMU8xTUQG1ZAaGB8NN8/jn6pus ynlk/bA0OHrMA== Message-ID: <58625a35-4a3e-4c91-939d-9f0d6635f8c0@kernel.org> Date: Thu, 26 Jun 2025 16:12:21 -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 v5 9/9] PCI: Add a new 'boot_display' attribute To: Bjorn Helgaas Cc: Bjorn Helgaas , Alex Deucher , =?UTF-8?Q?Christian_K=C3=B6nig?= , David Airlie , 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: <20250626204508.GA1639269@bhelgaas> Content-Language: en-US From: Mario Limonciello In-Reply-To: <20250626204508.GA1639269@bhelgaas> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 6/26/2025 3:45 PM, Bjorn Helgaas wrote: > On Tue, Jun 24, 2025 at 03:30:42PM -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 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. >> >> Signed-off-by: Mario Limonciello > > Acked-by: Bjorn Helgaas > > Question below. > >> --- >> v4: >> * new patch >> --- >> Documentation/ABI/testing/sysfs-bus-pci | 9 +++++++++ >> drivers/pci/pci-sysfs.c | 14 ++++++++++++++ >> 2 files changed, 23 insertions(+) >> >> diff --git a/Documentation/ABI/testing/sysfs-bus-pci b/Documentation/ABI/testing/sysfs-bus-pci >> index 69f952fffec72..897cfc1b0de0f 100644 >> --- a/Documentation/ABI/testing/sysfs-bus-pci >> +++ b/Documentation/ABI/testing/sysfs-bus-pci >> @@ -612,3 +612,12 @@ Description: >> >> # ls doe_features >> 0001:01 0001:02 doe_discovery >> + >> +What: /sys/bus/pci/devices/.../boot_display >> +Date: October 2025 >> +Contact: Linux PCI developers >> +Description: >> + This file indicates whether the device was used as a boot >> + display. If the device was used as the boot display, the file >> + will contain "1". If the device is a display device but wasn't >> + used as a boot display, the file will contain "0". > > Is there a reason to expose this file if it wasn't a boot display > device? Maybe it doesn't need to exist at all unless it contains "1"? I was mostly thinking that it's a handy way for userspace to know whether the kernel even supports this feature. If userspace sees that file on any GPU as it walks a list then it knows it can use that for a hint. But if you would rather it only shows up for the boot display yes it's possible to do I think. It's just more complexity to the visibility lookup to also call video_is_primary_device(). LMK which way you want to go and I'll respin the series with your tags and the robot fix. > >> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c >> index 268c69daa4d57..5bbf79b1b953d 100644 >> --- a/drivers/pci/pci-sysfs.c >> +++ b/drivers/pci/pci-sysfs.c >> @@ -30,6 +30,7 @@ >> #include >> #include >> #include >> +#include >> #include "pci.h" >> >> #ifndef ARCH_PCI_DEV_GROUPS >> @@ -679,6 +680,13 @@ const struct attribute_group *pcibus_groups[] = { >> NULL, >> }; >> >> +static ssize_t boot_display_show(struct device *dev, struct device_attribute *attr, >> + char *buf) >> +{ >> + return sysfs_emit(buf, "%u\n", video_is_primary_device(dev)); >> +} >> +static DEVICE_ATTR_RO(boot_display); >> + >> static ssize_t boot_vga_show(struct device *dev, struct device_attribute *attr, >> char *buf) >> { >> @@ -1698,6 +1706,7 @@ late_initcall(pci_sysfs_init); >> >> static struct attribute *pci_dev_dev_attrs[] = { >> &dev_attr_boot_vga.attr, >> + &dev_attr_boot_display.attr, >> NULL, >> }; >> >> @@ -1710,6 +1719,11 @@ static umode_t pci_dev_attrs_are_visible(struct kobject *kobj, >> if (a == &dev_attr_boot_vga.attr && pci_is_vga(pdev)) >> return a->mode; >> >> +#ifdef CONFIG_VIDEO >> + if (a == &dev_attr_boot_display.attr && pci_is_display(pdev)) >> + return a->mode; >> +#endif >> + >> return 0; >> } >> >> -- >> 2.43.0 >>