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 CA93312DDA1; Thu, 26 Jun 2025 23:33:20 +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=1750980801; cv=none; b=qiSjOj+UiZ7S5Ih7OQgV3nB9/3WPhb8Dwbmpxwvpy5eD7YSRvvSSImfR5J54MV1XvBjkRWLVKkH3B0TYBpWtNVVJgmX1HLFtsAHkK/SY3hJy9wTG4YbmigrbowK5CMlTXIn2k20H0po1TEiFTQ7HKSQaxAXO/eTagV1olSJo3KM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750980801; c=relaxed/simple; bh=vbC2GLOPug5kOMvejYkJyMkJ9xu1B3O8gjNYLt5ErVk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=URh/4PPzx8hXdYod+bsNtCjKDl7HcPrb/VT8CRaVsyYbxfmwjIIq+5bR358EHKwH+mjRRsRz7l3b4xd5sWTc4Vjwjx0dTXpiCf3H1OrZf0GFMVBVY3i4k/4WH3w2m+A8+E0baEtSlO68VzddD5+wo/529NNxrQ+cZtmUz+TbzCs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=DW9xo6/l; 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="DW9xo6/l" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 59CECC4CEEB; Thu, 26 Jun 2025 23:33:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1750980800; bh=vbC2GLOPug5kOMvejYkJyMkJ9xu1B3O8gjNYLt5ErVk=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=DW9xo6/lYAVQiwgc1gQ50Tgcs4VY4qQJqnlo3+KOkhY4Ig4ItPZ/hQ8pP8sl2717W LrXTt2n9Tuohuix3Qg8C0pWunv8kympVYEFcI7hS/fGqIaLGL8da1MH/Ar6JXnH6FT bsDihuEDI4RD0UegoB2QyZiRSa/f1Z02MM1O0jPa3Lzb8tyVCrmjqUTl9oAkewG/CN dmnglJAANFHsnviXQc7QcSktYcwsm1e3esJTNxIN2QLkbt/mJGFFeOxzccZGLI2gyB 6beMyO8BIt4Elomey3lOqu0ZYg0kygV3LmEtminDytwzgzLC3jZPpeQVbFh8q1ztQG CjxHW59JgL7RQ== Message-ID: <5cc01163-1feb-4a18-8060-27f4da39b2e4@kernel.org> Date: Thu, 26 Jun 2025 18:33:15 -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: <20250626214721.GA1642412@bhelgaas> Content-Language: en-US From: Mario Limonciello In-Reply-To: <20250626214721.GA1642412@bhelgaas> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit 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. > >>>> 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 >>>> >>