Hi

Am 15.10.21 um 01:28 schrieb bugzilla-daemon@bugzilla.kernel.org:
> https://bugzilla.kernel.org/show_bug.cgi?id=214725
> 
>              Bug ID: 214725
>             Summary: simpledrm and i915 both active after boot
>             Product: Drivers
>             Version: 2.5
>      Kernel Version: 5.14.11
>            Hardware: All
>                  OS: Linux
>                Tree: Mainline
>              Status: NEW
>            Severity: normal
>            Priority: P1
>           Component: Video(DRI - non Intel)
>            Assignee: drivers_video-dri@kernel-bugs.osdl.org
>            Reporter: dennis.lissov@gmail.com
>          Regression: No
> 
> Gentoo Linux, custom kernel build, 5.14.11 with
> CONFIG_DRM_SIMPLEDRM=y
> CONFIG_DRM_I915=y
> 
> Plasma (wayland) sees two monitors: the laptop screen and an unknown one. The
> only monitor physically present is the laptop screen. This did not happen a few
> months ago (possibly started with 5.14 upgrade).
> 
> $ ls /sys/class/drm/
> card0  card0-eDP-1  card1  card1-Unknown-1  card2  card2-DP-1  card2-DP-2
> card2-DP-3  renderD128  renderD129  version
> $ readlink /sys/class/drm/card0 # Intel GPU
> ../../devices/pci0000:00/0000:00:02.0/drm/card0
> $ readlink /sys/class/drm/card1 # Simple DRM
> ../../devices/platform/simple-framebuffer.0/drm/card1
> $ readlink /sys/class/drm/card2 # Nouveau (not used at the moment)
> ../../devices/pci0000:00/0000:00:01.0/0000:01:00.0/drm/card2
> 
> $ dmesg | egrep '(simple|i915)'
> [    0.000000] Command line: BOOT_IMAGE=/kernel-5.14.11 root=[...] ro
> acpi_backlight=video resume=[...] i915.enable_gvt=1 quiet
> [    0.060342] Kernel command line: BOOT_IMAGE=/kernel-5.14.11 root=[...] ro
> acpi_backlight=video resume=[...] i915.enable_gvt=1 quiet
> [    1.076957] i915 0000:00:02.0: [drm] VT-d active for gfx access
> [    1.076961] i915 0000:00:02.0: vgaarb: deactivate vga console
> [    1.387359] i915 0000:00:02.0: Direct firmware load for
> i915/gvt/vid_0x8086_did_0x191b_rid_0x06.golden_hw_state failed with error -2
> [    1.404418] i915 0000:00:02.0: vgaarb: changed VGA decodes:
> olddecodes=io+mem,decodes=none:owns=io+mem
> [    1.404525] i915 0000:00:02.0: [drm] Disabling framebuffer compression (FBC)
> to prevent screen flicker with VT-d enabled
> [    1.404931] i915 0000:00:02.0: [drm] Finished loading DMC firmware
> i915/skl_dmc_ver1_27.bin (v1.27)
> [    1.422128] [drm] Initialized i915 1.6.0 20201103 for 0000:00:02.0 on minor
> 0
> [    1.425127] [drm] Initialized simpledrm 1.0.0 20200625 for
> simple-framebuffer.0 on minor 1
> [    1.437859] simple-framebuffer simple-framebuffer.0: [drm] fb0: simpledrm
> frame buffer device
> [    1.438058] fbcon: i915 (fb1) is primary device
> [    2.579133] i915 0000:00:02.0: [drm] fb1: i915 frame buffer device
> [   22.162612] snd_hda_intel 0000:00:1f.3: bound 0000:00:02.0 (ops
> i915_audio_component_bind_ops)
> [   52.106084] simple-framebuffer simple-framebuffer.0: swiotlb buffer is full
> (sz: 8388608 bytes), total 32768 (slots), used 0 (slots)
> 
> Looks like the hand-over mechanism does not correctly handle this combination,
> possibly due to i915 loading before simpledrm.
> 

Interesting. There are two workarounds:

  * build every driver except simpledrm as module, or
  * don't build simpledrm on yur system (it's Gentoo)

I don't think that linking all driver into the kernel worked before 
simpledrm. Before simpledrm there would be simplefb, efifb or vesafb. 
Those drivers use a similar handover scheme, which would have failed in 
a similar way.

Best regards
Thomas

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev