Linux >= 5.14.12 and 5.15-rc5 fail to show anything on the screen with CONFIG_DRM_SIMPLEDRM=y

[Artem S. Tashkinov]

Hello,

Kernel 5.14.12 introduced this change, git commit
ec7cc3f74b4236860ce612656aa5be7936d1c594:

--- a/linux-5.14.11/drivers/video/fbdev/Kconfig
+++ b/linux-5.14.12/drivers/video/fbdev/Kconfig
@@ -2191,8 +2191,9 @@ config FB_HYPERV
       This framebuffer driver supports Microsoft Hyper-V Synthetic Video.

  config FB_SIMPLE
-   bool "Simple framebuffer support"
-   depends on (FB = y) && !DRM_SIMPLEDRM
+   tristate "Simple framebuffer support"
+   depends on FB
+   depends on !DRM_SIMPLEDRM
     select FB_CFB_FILLRECT
     select FB_CFB_COPYAREA
     select FB_CFB_IMAGEBLIT


However if you enable CONFIG_DRM_SIMPLEDRM=y along with it, the system
will show a black screen on boot while logging these messages:

[drm] Initialized simpledrm 1.0.0 20200625 for simple-framebuffer.0 on
minor 0
simple-framebuffer simple-framebuffer.0: [drm] *ERROR* fbdev: Failed to
setup generic emulation (ret=-22)
fbcon: Taking over console


When CONFIG_DRM_SIMPLEDRM is disabled it proceeds to boot normally:

simple-framebuffer simple-framebuffer.0: framebuffer at 0xe1000000,
0x300000 bytes
simple-framebuffer simple-framebuffer.0: format=a8r8g8b8,
mode=1024x768x32, linelength=4096
fbcon: Deferring console take-over
simple-framebuffer simple-framebuffer.0: fb0: simplefb registered!


This is discussed here: https://bugzilla.kernel.org/show_bug.cgi?id=214723

I really don't know what to make of it but I definitely don't like this
situation.


Best regards,
Artem