[U-Boot] Preserving frame buffer memory between uboot and Linux

[Wolfgang Denk]

Dear Steven Zedeck,

In message <25722060.post at talk.nabble.com> you wrote:
> 
> We have a situation when we want to display an image towards the end of
> Uboot's execution, before we boot Linux. I have that already.
> 
> However, my issue is that while Linux boots it mallocs a new frame buffer
> and reinitializes the LCD controller with a new memory address. At the
> moment in Uboot the frame buffer is at 0x23F39000. In Linux I see it being
> mapped to 0x23980000.
> 
> Is there a way to force Linux to use the already-allocated frame buffer
> memory so the image doesn't go away?

In mainline: not, or not yet at least. 

In our linux-2.6-denx repo you can find these commits:

commit 01baab26e52bc66cb1781ab970fba932b592f2ee
Author: Anatolij Gustschin <agust at denx.de>
Date:   Wed May 28 23:45:21 2008 +0200

    Fix to enable console cursor drawing capability if CONFIG_FB_PRE_INIT_FB defined
    
    Background:
      By defining the CONFIG_FB_PRE_INIT_FB option in the
      Linux kernel configuration the framebuffer state
      set by the boot loader before booting the Linux kernel
      will be preserved in order to avoid display flicker and
      splash screen destruction. To ensure this, this option
      also disabled framebuffer console cursor drawing capability
      entirely. This was pretty invasive restriction and didn't
      allow using console cursor drawing later in applications
      which need the visible cursor.
    
      Now this patch is introduced to get rid of this restriction.
      If CONFIG_FB_PRE_INIT_FB is defined in the Linux kernel
      configuration, the framebuffer state will still be preserved
      (as set by the boot loader) and also framebuffer console
      cursor drawing will be disabled. If an application needs
      visible cursor, it should enable cursor drawing by writing
      escape sequence ESC[?25h to the console device.
      E.g. echo -e "\33[?25h" > /dev/tty0
    
    Signed-off-by: Anatolij Gustschin <agust at denx.de>
...
commit 6c3b5cdbc84b43190996124debc8fb29c9bf90ed
Author: Anatolij Gustschin <agust at denx.de>
Date:   Tue Jan 15 00:28:23 2008 +0100

    Add CONFIG_FB_PRE_INIT_FB option
    
    CONFIG_FB_PRE_INIT_FB option allows to inherit
    display controller configuration and framebuffer
    contents from the state set by the bootloader.
    
    Signed-off-by: Anatolij Gustschin <agust at denx.de>

They do exactly what you are looking for. I remember that someone
tried to clean this up and poush it into mainline, but IIRC this
attempt failed because the PTB considered this an exotic requirement
from those insane embedded folks which was not needed on any real
systems.

> I am running on an Atmel AT91SAM9RL with Uboot 2008.10 and 2.6.28 Linux.

Hope this helps.

Best regards,

Wolfgang Denk

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