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

[Thomas Zimmermann]

Hi

Am 22.10.21 um 14:15 schrieb 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.

You might need commit b693e42921e0 ("drm/fbdev: Clamp fbdev surface size 
if too large"), which is only in -rc6.

Alternatively, make sure that fbdev overallocation has been disabled. 
The config that is attached to that bug report indicate that it's enabled.

   CONFIG_DRM_FBDEV_OVERALLOC=300

Temporarily set this value to 100 for now.

Sorry for any problems with simpledrm. It's still new and we're fixing 
the bug that it exposes.

BTW, you also have to make your bootloader pass the graphics mode to 
Linux. (GRUB_GFXPAYLOAD_LINUX="keep" for GRUB [1]).

Best regards
Thomas

[1] https://www.gnu.org/software/grub/manual/grub/html_node/gfxpayload.html

> 
> 
> Best regards,
> Artem

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