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

[Steven Zedeck <saz@proliphix.com>]

wd wrote:
> 
> Dear Steven Zedeck,
> 
> In message <25722060.post@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@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@denx.de>
> ...
> commit 6c3b5cdbc84b43190996124debc8fb29c9bf90ed
> Author: Anatolij Gustschin <agust@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@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
> 
> -- 
> DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
> HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
> Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
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> 
> 

Wolfgang,
Thanks for the reply. I did a search on our entire Linux code base for
CONFIG_FB_PRE_INIT_FB and it only appears in one file
drivers/video/mb862xx/mb862xxfb.c

I don't understand how to set this variable in my specific configuration
file.

I did, however, see this in atmel_lcdfb.c:
map = platform_get_resource(pdev, IORESOURCE_MEM,1);
if (map)
{
   /* use a pre-allocated memory buffer (/
.
.
.
   /* Don't clear the frame buffer -- someone may have set up a splash
image. */

.
.

}

Isn't this what I need to be concerned about? If so, what do I need to do un
Uboot to make this take effect?

Thanks,
Steve

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