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 6D2DD2904; Fri, 27 Jun 2025 16:15:54 +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=1751040955; cv=none; b=Zwwcxx6zrJUKlg03/mPVqyl/41zsuEE2wy/X7YdytZhvHk/p4r03PIOmSwtOff6QLSLmtXpkzaUbc3SEDSLYa645qrV64PBfKWKqHq191qRu+7EdVV9/OEI5SgH7ZMiNfQYwxp4TCAvPtGalhDeVAFE45pysE/4FBTDO7Nga9a0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1751040955; c=relaxed/simple; bh=ngjP2j/mogEBHJHVAdxePa/ZTfx8oWY4hps0ZIisoVM=; h=Date:From:To:Cc:Subject:Message-ID:MIME-Version:Content-Type: Content-Disposition:In-Reply-To; b=asE4CWgXbeXpaf6J6rwIPDHuI+KP2V+56GYnnFJHHcw1JozwTIAJ0+4Bo4V63L28HhEmmJxpXgw7JDfCCuvUFfpB0hOomWaLbRO1DB8w1QKNcxg0JyjzhxgyyvPalB2b+cE918I90lIDSWVpCrFHHVVFsu3qOuuoc2JuthUoOHQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=d3pfO07Y; 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="d3pfO07Y" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B0DEAC4CEE3; Fri, 27 Jun 2025 16:15:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1751040953; bh=ngjP2j/mogEBHJHVAdxePa/ZTfx8oWY4hps0ZIisoVM=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=d3pfO07YLCIK1I43m79Ck6t80cQIjU0rIm1HCmhgWy+yeE0cyqsL6+xQ78s/Mn//j HA//ehNfgC/ue6v0at98gGIDu73K9Tny0zIY9K14a7CUWza29A19uWAsLKtroQ/HN6 7ysGjEs5pDT8rTa0uUg30IBvvS/55l7xkYGo63rew18C3Qgf/yKOuqVaUpv81a2coD FBv1qJe0+TQvQgR1duQ2iJmAU+hSAYuZpcCB14O6ytfEFOoOCfYKED2M6DvC354U5x djlnN1/jqbuJeWOXwRgHOZ2Uxv2GL3PzvoSt3fu0nwbSBoVBa/CENboYJGRPOH0b3X k1lsRpMl0X3eg== Date: Fri, 27 Jun 2025 11:15:52 -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: <20250627161552.GA1671755@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: <5cc01163-1feb-4a18-8060-27f4da39b2e4@kernel.org> On Thu, Jun 26, 2025 at 06:33:15PM -0500, Mario Limonciello wrote: > On 6/26/25 4:47 PM, Bjorn Helgaas wrote: > > 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". > > I did an experiment with this but the PCI resources aren't ready at the time > visibility is determined. > > So either: > * the sysfs file creation needs to be deferred similar to > pci_create_resource_files() does > > or > > * call to sysfs_update_group() is needed to recalculate visibility. Sigh, yeah, that's an old annoying problem. I think deferring as you did is fine. > > > > > 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 > > > > > > > > >