[Bug 2142086] [NEW] simpledrm fails to hand off /dev/dri/card0 to amdgpu on Picasso/Raven2, causing GDM crash and black screen

Public bug reported:

Affects:
Ubuntu 24.04.3 LTS, Kernel 6.17.0-14-generic
Hardware:
AMD Picasso/Raven 2 [Radeon Vega Series] [1002:15d8]
Description:
On AMD Picasso/Raven2 APUs, the simpledrm framebuffer driver initializes during early boot and claims /dev/dri/card0. When the amdgpu driver loads ~16 seconds later, simpledrm fails to properly hand off the device. This forces amdgpu to register as /dev/dri/card1 instead.
GDM/GNOME Shell expects the primary GPU at card0. When it finds simpledrm there (which cannot do hardware-accelerated rendering), it crashes with:
Failed to ensure KMS FB ID on /dev/dri/card0: drmModeAddFB failed: No such device
GDM automatically retries and eventually discovers card1 (the real amdgpu), but this causes:

Login screen crash on first attempt
Black screen with cursor for ~5-10 seconds
Random boot failures requiring multiple reboots

Steps to Reproduce:

Boot Ubuntu 24.04.3 with kernel 6.17.0-14 on AMD Picasso/Raven2 hardware
Observe black screen after UEFI logo
Check ls -la /dev/dri/ from TTY2 → shows only card1
Check dmesg → simpledrm on minor 0, amdgpu on minor 1

Expected:
amdgpu should claim /dev/dri/card0, GDM should start cleanly
Actual:
simpledrm blocks card0, amdgpu gets card1, GDM crashes and retries
Workaround:
Add to /etc/default/grub:
GRUB_CMDLINE_LINUX_DEFAULT="... initcall_blacklist=simpledrm_platform_driver_init"
Then sudo update-grub and reboot.
This prevents simpledrm from loading, allowing amdgpu to properly claim card0.
Attachments:

bug-card1-proof.txt (shows card1 without workaround)
bug-dmesg-card1.txt (kernel logs showing simpledrm/amdgpu conflict)
bug-gnome-crash.txt (GDM crash and retry sequence)

** Affects: linux (Ubuntu)
Importance: Undecided
Status: New


** Tags: amdgpu drm gdm picasso raven2 simpledrm

** Attachment added: "Full dmesg log showing simpledrm minor 0 and amdgpu minor 1"
https://bugs.launchpad.net/bugs/2142086/+attachment/5946938/+files/bug-gnome-crash.txt

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https://bugs.launchpad.net/bugs/2142086

Title:
simpledrm fails to hand off /dev/dri/card0 to amdgpu on
Picasso/Raven2, causing GDM crash and black screen

Status in linux package in Ubuntu:
New

Bug description:
Affects:
Ubuntu 24.04.3 LTS, Kernel 6.17.0-14-generic
Hardware:
AMD Picasso/Raven 2 [Radeon Vega Series] [1002:15d8]
Description:
On AMD Picasso/Raven2 APUs, the simpledrm framebuffer driver initializes during early boot and claims /dev/dri/card0. When the amdgpu driver loads ~16 seconds later, simpledrm fails to properly hand off the device. This forces amdgpu to register as /dev/dri/card1 instead.
GDM/GNOME Shell expects the primary GPU at card0. When it finds simpledrm there (which cannot do hardware-accelerated rendering), it crashes with:
Failed to ensure KMS FB ID on /dev/dri/card0: drmModeAddFB failed: No such device
GDM automatically retries and eventually discovers card1 (the real amdgpu), but this causes:

Login screen crash on first attempt
Black screen with cursor for ~5-10 seconds
Random boot failures requiring multiple reboots

Steps to Reproduce:

Boot Ubuntu 24.04.3 with kernel 6.17.0-14 on AMD Picasso/Raven2 hardware
Observe black screen after UEFI logo
Check ls -la /dev/dri/ from TTY2 → shows only card1
Check dmesg → simpledrm on minor 0, amdgpu on minor 1

Expected:
amdgpu should claim /dev/dri/card0, GDM should start cleanly
Actual:
simpledrm blocks card0, amdgpu gets card1, GDM crashes and retries
Workaround:
Add to /etc/default/grub:
GRUB_CMDLINE_LINUX_DEFAULT="... initcall_blacklist=simpledrm_platform_driver_init"
Then sudo update-grub and reboot.
This prevents simpledrm from loading, allowing amdgpu to properly claim card0.
Attachments:

bug-card1-proof.txt (shows card1 without workaround)
bug-dmesg-card1.txt (kernel logs showing simpledrm/amdgpu conflict)
bug-gnome-crash.txt (GDM crash and retry sequence)

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