maintainer-feedback requested: [Bug 278082] AMD Ryzen 7 PRO 7840U's internal GPU not supported

Bugzilla Automation <bugzilla@FreeBSD.org> has asked freebsd-x11 (Nobody)
<x11@FreeBSD.org> for maintainer-feedback:
Bug 278082: AMD Ryzen 7 PRO 7840U's internal GPU not supported
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=278082



--- Description ---
The integrated GPU on an AMD Ryzen 7 PRO 7840U seems not to be supported. The
machine in question is a Lenovo Thinkpad P16s G2 (AMD; Type 21K9) running a
recent version of FreeBSD 15:
FreeBSD perugia 15.0-CURRENT FreeBSD 15.0-CURRENT #0 main-n269029-a983cea4e9a8:
Thu Mar 28 17:26:19 CET 2024	
root@perugia:/usr/obj/usr/src/amd64.amd64/sys/GENERIC amd64

dmesg reports about the CPU as follows:
----8<----
CPU: AMD Ryzen 7 PRO 7840U w/ Radeon 780M Graphics   (3293.91-MHz K8-class CPU)
  Origin="AuthenticAMD"  Id=0xa70f41  Family=0x19  Model=0x74  Stepping=1
---->8----

pciconf -lv reports about the graphics controller:
----8<----
vgapci0@pci0:100:0:0:	class=0x030000 rev=0xdd hdr=0x00 vendor=0x1002
device=0x15bf subvendor=0x17aa subdevice=0x50da
    vendor     = 'Advanced Micro Devices, Inc. [AMD/ATI]'
    device     = 'Phoenix1'
    class      = display
    subclass   = VGA
---->8----

Loading amdgpu.ko from graphics/drm-515-kmod works fine, but none of the
available firmware modules fits. Loading amdgpu.ko from graphics/drm-61-kmod
causes a kernel panic (see attachments).

Prior to installing FreeBSD, this machine ran fine -- graphics included -- with
Lubuntu 22.04.3.

This might be related to Bug 268394; the interim solution presented there
unfortunately doesn't work in this case as we can't fit a dedicated graphics
card.