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 8D01A1DF980; Thu, 26 Jun 2025 21:47:23 +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=1750974443; cv=none; b=f1BDn3b+XdWWLZTBBD2IhwTs+FjCDElAXhtGw0+Eyomb0GAEH1W9XDFHK+DjfP/uTBi82sB+RdJfmYfwnOW92qrMNq+5VeSDW73OG4nJdFnd+h20K2Z+OCAaqsKBiq4nQLl0VRmhxQcGEoGqFxjncfXtgCYeYXJlPH3P3DtmWYc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750974443; c=relaxed/simple; bh=hxQVzBMNwyC88HTo8GzVCXXrinORweyOG/ceTNc1kGM=; h=Date:From:To:Cc:Subject:Message-ID:MIME-Version:Content-Type: Content-Disposition:In-Reply-To; b=vABZW1PEqBJwo8pbdEzIQXuxNat1PhMRB+YTWpNonAflQvV/Di1wfzi6SG13S4lnKU80A+fgbXi79ZZpW8WW2AdgvA32wP/8Fl9ay2ud6VWcbzAuhvYLsK2ec7SBExzpNe5yoUathTCBBWCXATlaA7QJNn608FN7zgEYtDt/NvQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=UgXmVwi2; 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="UgXmVwi2" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DB0A8C4CEEB; Thu, 26 Jun 2025 21:47:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1750974443; bh=hxQVzBMNwyC88HTo8GzVCXXrinORweyOG/ceTNc1kGM=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=UgXmVwi2rCspNSmYuTGBVBB5eZtbt0N8aMBn19wXnNbJDBpzVoKGeEI8qzxdZLWqu 1Ynn3B8WPGbXQbmkMpuWmrRzpEElcnoGHQv5OXP6j66CtEr6Szwb0G6kWjDE4+0Evp SmfOa6ipBqiY8TMUW12WOhwBER/p7n3saqwFiWmdHO2ALllJtX+QP5pMHySRCHR3tp H4oLzTFK4nmOUf5SnEGTBdjkW2Dt+Xcp+K4Q+NqVYSq3VRAzx4piP5uFPMlrHovCye uZ7KbYkkIQJeAit/jV3So7jOqhyet5n5U6Gaxdth/dF0Qy0yGwwqF8o/ZYJuUeUUUX 3at8xacc2T1Zw== Date: Thu, 26 Jun 2025 16:47:21 -0500 From: Bjorn Helgaas To: Mario Limonciello Cc: Bjorn Helgaas , Alex Deucher , Christian =?utf-8?B?S8O2bmln?= , 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 Subject: Re: [PATCH v5 9/9] PCI: Add a new 'boot_display' attribute Message-ID: <20250626214721.GA1642412@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: <58625a35-4a3e-4c91-939d-9f0d6635f8c0@kernel.org> On Thu, Jun 26, 2025 at 04:12:21PM -0500, Mario Limonciello wrote: > 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(). I think for a singleton situation like this it makes more sense to only expose the file for one device, not several files where only one of them contains "1". > > > 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 > > > >