framebuffer swap endianess

framebuffer swap endianess

[Angelo]

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Hi, i'm angelo.

I have just create a framebuffer for an embedded system:
- powerpc (little endian)  with  a GPU (big endian).

I'm working on linux 2.6.22

When i try to execute Xfbdev, it starts but with wrong colors.
I need to swap the RGB format (RRRRRGGGGGGBBBBB) to BGR, respecting the endianess (GGGRRRRRBBBBBGGG).

I know that X loads with some ioctl, the principal settings through framebuffer.
But i'm not sure if framebuffer can inform it on the RGB format.

I also tried to change something on cmap, but nothing changes on display;

So, i hope you can help me. 

Many thanks.


       
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Re: framebuffer swap endianess

[Josh Boyer]

On Tue, 22 Jan 2008 16:46:47 +0100 (CET)
Angelo <s104259@yahoo.it> wrote:

> Hi, i'm angelo.
> 
> I have just create a framebuffer for an embedded system:
> - powerpc (little endian)  with  a GPU (big endian).

I think you have those backwards?  PowerPC is big-endian...

josh

Re: framebuffer swap endianess

[Roman Fietze]

Hello ANgelo,

On Tuesday 22 January 2008 16:46:47 Angelo wrote:

> I have just create a framebuffer for an embedded system:
> - powerpc (little endian)  with  a GPU (big endian).

Are you sure? Isn't it the other way around?

> When i try to execute Xfbdev, it starts but with wrong colors.  I
> need to swap the RGB format (RRRRRGGGGGGBBBBB) to BGR, respecting
> the endianess (GGGRRRRRBBBBBGGG).

We modified the X Server and swapped when transferring from the shadow
buffer to the video buffer. That cured all our problems. This was on
the 2.4.25 from DENX and with Xfree86.

Other modifications like changing the RGB masks for the display/screen
only helped partwise, because some applications just ignored that when
using some image formats.


Roman

=2D-=20
Roman Fietze Telemotive AG B=FCro M=FChlhausen

Re: framebuffer swap endianess

[Kumar Gala]

On Jan 23, 2008, at 1:39 AM, Roman Fietze wrote:

> Hello ANgelo,
>
> On Tuesday 22 January 2008 16:46:47 Angelo wrote:
>
>> I have just create a framebuffer for an embedded system:
>> - powerpc (little endian)  with  a GPU (big endian).
>
> Are you sure? Isn't it the other way around?

we are sure.  Linux only supports PPC in big endian mode.

  - k

framebuffer swap endianess

[Angelo]

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Hello all, 

many thanks for your answer.

Modify the X server is a good idea.
I'd just tried to understand the exact place to make changes. Adding many "printf" to understand it.
But it's very complex.

>We modified the X Server and swapped when transferring from the shadow
>buffer to the video buffer. That cured all our problems. 

Could you tell me where is the exact place to do this? in some files like fbdev.c or other?

>This was on the 2.4.25 from DENX and with Xfree86.

Sorry but i don't understand this sentence.

Anyway many thanks.


       
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Re: framebuffer swap endianess

[Roman Fietze]

Hello Angelo,

Question to the mailing list readers: is it ok to post an xfree86 or
xorg patch in this mailing list (about 9KiB), or would it be better to
mail that patch to Angelo directly? Thanks.


On Thursday 24 January 2008 15:27:12 Angelo wrote:

> Modify the X server is a good idea.

Sure, if you know where. It took us some time to find "the" correct
place. But see below. :)

> Could you tell me where is the exact place to do this? in some files like
> fbdev.c or other?

The major changes are inside programs/Xserver/miext/shadow/shpacked.c
of either the xorg or xfree86 version of the X server. The swap is
done when copying the data from the shadow buffer to the video memory.

Another place is programs/Xserver/hw/xfree86/drivers/fbdev/fbdev.c,
but here we just setup the Screen correctly, so our new swapping
shadow buffer update route will be used.

> >This was on the 2.4.25 from DENX and with Xfree86.
>
> Sorry but i don't understand this sentence.

We were using Linux 2.4.25 for the PowerPC from DENX and the XFree86 X
Server. The kernel version shouldn't be a problem at all, and I think
the patches should work on either X Server version, Xorg or Xfree86.


Roman

=2D-=20
Roman Fietze Telemotive AG B=FCro M=FChlhausen

Re: framebuffer swap endianess

[Clemens Koller]

Roman Fietze schrieb:
> Hello Angelo,
> 
> Question to the mailing list readers: is it ok to post an xfree86 or
> xorg patch in this mailing list (about 9KiB), or would it be better to
> mail that patch to Angelo directly? Thanks.

I'm interested in it. Please, at least, CC me. :-)
I was having similar issues with my SM501/SM502 on MPC8540/MPC8548.
But due to other projects I had to slow down a bit that area.

Thank you,

Clemens