Dell Latitude/Precision, sig=0x806ec/20090609: Linux hangs without plugged in power cable

Already present reported in project *dell-sputnik*. (Note, it happened here also without suspend/resume.):

1. https://bugs.launchpad.net/dell-sputnik/+bug/1661741
2. Quote from https://bugs.launchpad.net/dell-sputnik/+bug/1661741/comments/26:

    > A similar bug affects several Dell laptop models:
    > - Dell 5480/5488 :
    > https://bugs.launchpad.net/dell-sputnik/+bug/1866343
    > - Dell E5470 :
    > https://bugs.launchpad.net/dell-sputnik/+bug/1661741
    > (Note that the bug https://bugs.launchpad.net/dell-sputnik/+bug/1661741 is not fixed; it has been changed, by error, to fixed. Please, it will be nice if somebody can change the status to "confirmed")
    > - Dell 7740 :
    > https://bugs.launchpad.net/dell-sputnik/+bug/1871491
    >
    > I suppose that the bug can also affect Dell precision 7730

After experiencing this already on the Dell Latitude 5480/5488 (https://bugs.launchpad.net/dell-sputnik/+bug/1866343), we have seen this now too with the Dell Precision 3540 (with dedicated AMD graphics card).

Without the power cord plugged in, the system started fine, then updating packages, including the Linux kernel, turning the system off, and right back on, it went to GRUB, and GRUB was able to load Linux and initrd, and starting Linux it hung.

Num lock key didn’t respond (but also didn’t blink – no idea if this should work), and Ctrl + Alt + Del didn’t work either. So, the system had to be powered off by pressing the power button for some (ten(?)) seconds.

Subsequent tries didn’t help, until we remembered the issues with the other device, and plugging in the power cord fixed it.

With the power cable unplugged, it didn’t boot.

The state of the connected power cable only mattered, when starting the Linux kernel. That means, plugging it in, when GRUB was active, the system booted. Removing the cable, when GRUB was running, Linux hung.

I tried to get Linux messages, but `debug nomodeset earlyprintk=efi` didn’t get Linux to output any messages.

### Workarounds ###

I was able to get Linux booting by adding either one of the following Linux kernel parameters.

1. `maxcpus=1` (once it started with `maxcpus=2`)
2. `nosmp`
2. `acpi=off`
3. `nolapic`

In this state, there was only one CPU online. Trying to bring one more online, the system always froze instantly.

    echo 1 | sudo tee /sys/devices/system/cpu/cpu1/online

(Nothing in pstore either.) (Where maxcpus=2` worked, we were able to bring a third CPU online, but the system froze when trying the fourth.)

### Reproducibilty ###

Letting the system sit over night, and trying again in the morning, unfortunately, we did *not* test without a power cable plugged in, as we had an idea to test the non-USB-Type-C power cable. With that the system started.

Powering the system off, and unplugging the cable, the system booted without issues. So something changed.

We weren’t able to get it into a state, where it doesn’t boot in the last hour, but we would like this investigated, as we are giving these systems to our users.