[PATCH v8 9/9] PCI: Add a new 'boot_display' attribute

[Mario Limonciello]

On 7/16/25 3:22 AM, Maxime Ripard wrote:
> Hi Mario,
> 
> On Mon, Jul 14, 2025 at 04:21:46PM -0500, Mario Limonciello wrote:
>> From: Mario Limonciello <mario.limonciello at amd.com>
>>
>> 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.
>>
>> Reviewed-by: Thomas Zimmermann <tzimmermann at suse.de>
>> Signed-off-by: Mario Limonciello <mario.limonciello at amd.com>
>> ---
>> v7:
>>   * fix lkp failure
>>   * Add tag
>> v6:
>>   * Only show for the device that is boot display
>>   * Only create after PCI device sysfs files are initialized to ensure
>>     that resources are ready.
>> v4:
>>   * new patch
>> ---
>>   Documentation/ABI/testing/sysfs-bus-pci |  8 +++++
>>   drivers/pci/pci-sysfs.c                 | 46 +++++++++++++++++++++++++
>>   2 files changed, 54 insertions(+)
>>
>> diff --git a/Documentation/ABI/testing/sysfs-bus-pci b/Documentation/ABI/testing/sysfs-bus-pci
>> index 69f952fffec72..8b455b1a58852 100644
>> --- a/Documentation/ABI/testing/sysfs-bus-pci
>> +++ b/Documentation/ABI/testing/sysfs-bus-pci
>> @@ -612,3 +612,11 @@ Description:
>>   
>>   		  # ls doe_features
>>   		  0001:01        0001:02        doe_discovery
>> +
>> +What:		/sys/bus/pci/devices/.../boot_display
>> +Date:		October 2025
>> +Contact:	Linux PCI developers <linux-pci at vger.kernel.org>
>> +Description:
>> +		This file indicates the device was used as a boot
>> +		display. If the device was used as the boot display, the file
>> +		will be present and contain "1".
> 
> It would probably be a good idea to define what a "boot display" here
> is. I get what you mean, but it's pretty vague and could easily be
> misunderstood.
> 
> Maxime

Here's my proposal for updated text, can you please bikeshed or propose 
an alternative?

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".