Re: OptiPlex 7400 AIO HDMI-IN button requires WMI startup method

[Teodora <teolyub@gmail.com>]

Hi,

I have a Dell OptiPlex 7400 All-in-One machine and have been 
investigating why its physical HDMI-In/source button works under 
Windows but not under Linux. I wanted to flag a potential solution, 
though I am not a kernel developer but was hoping that perhaps this 
could help the community.

So, my system details are:

- Dell OptiPlex 7400 All-in-One
- Fedora 44
- Kernel: 7.2.11-200.fc44.x86_64
- dell-wmi-aio is present and loaded

While investigating the Dell Windows OSD software, I found that the 
button generates a WMI event through Acpi_OSD_event, GUID: 
02314822-307C-4F66-BF0E-48AEAEB26CC8. The GDat payload generated when 
pressing the source button begins 02 00 00 00 F2 DD which corresponds 
to event/scancode 0xDDF2.

More importantly, Dell's OSD service invokes another WMI method during 
startup:

    Class: AcpiOSD_WMBC_method
    GUID: 2D703EE8-36AC-4F88-BDB5-7556CE6B2946

    Method: PegaOemNotificationStartUp
    WmiMethodId: 1
    Description: "Invoked by AP when system up."

Linux exposes this WMI interface on the machine, with instance_count = 
1. I wrote a minimal test WMI driver which binds only to this GUID and 
invokes: wmidev_invoke_procedure(wdev, 0, 1, &input); using an empty 
input buffer.

The result is reproducible: After a normal Linux boot, the HDMI/source 
button does not switch the display. Then loading the test driver 
invokes WMI method 1 and the firmware reports success. Immediately 
after, the physical source button works correctly and switches the 
panel to HDMI-In. The test module can then be unloaded and the physical 
button continues to work.

After rebooting, the problem returns until method 1 is invoked again. 
This suggests that PegaOemNotificationStartUp is a one-shot firmware 
initialization which Dell's Windows software performs at startup but 
Linux currently does not.

Below I am sharing the small module I use as a workaround; this is 
loaded once on boot.

// SPDX-License-Identifier: GPL-2.0

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/wmi.h>

#define DELL_OSD_WMI_GUID "2D703EE8-36AC-4F88-BDB5-7556CE6B2946"
#define DELL_OSD_STARTUP_METHOD 1

static int dell_osd_probe(struct wmi_device *wdev, const void *context)
{
 struct wmi_buffer input = {
  .length = 0,
  .data = NULL,
 };

 u8 instances;
 int ret;

 (void)context;

 instances = wmidev_instance_count(wdev);

 dev_info(&wdev->dev,
   "Dell OSD test: WMI device found, instance count = %u\n",
   instances);

 if (instances < 1) {
  dev_err(&wdev->dev,
   "Dell OSD test: no WMI instance 0 available\n");
  return -ENODEV;
 }

 dev_info(&wdev->dev,
   "Dell OSD test: calling PegaOemNotificationStartUp, method ID 1\n");

 ret = wmidev_invoke_procedure(
  wdev,
  0,
  DELL_OSD_STARTUP_METHOD,
  &input
 );

 if (ret < 0) {
  dev_err(&wdev->dev,
   "Dell OSD test: startup method failed: %d\n",
   ret);
  return ret;
 }

 dev_info(&wdev->dev,
   "Dell OSD test: startup method returned success\n");

 return 0;
}

static const struct wmi_device_id dell_osd_id_table[] = {
 {
  .guid_string = DELL_OSD_WMI_GUID,
 },
 { }
};

MODULE_DEVICE_TABLE(wmi, dell_osd_id_table);

static struct wmi_driver dell_osd_driver = {
 .driver = {
  .name = "dell-osd-wmi-test",
 },
 .id_table = dell_osd_id_table,
 .probe = dell_osd_probe,
 .no_singleton = true,
};

module_wmi_driver(dell_osd_driver);

MODULE_AUTHOR("Dell OptiPlex 7400 AIO experimental test");
MODULE_DESCRIPTION("Experimental Dell OSD WMI startup-method test");
MODULE_LICENSE("GPL");

I hope this would be useful as not having this function has been such a 
bugbear for me over the years, especially on a business machine.

Thanks,
Teodora