How to shift color bits in fbdev?

[Gregoire Gentil]

Hello,

I'm using fbdev with xorg on a hardware prototype and unfortunately, the
video wires at the output of the chip have been mixed and swapped. To
make it work properly on this proto (I can't afford to do immediately
another revision), I need to shift and swap some bits for each RGB24
pixel. Can anyone tell me where I could patch to achieve such objective?
Is it in xf86-video-fbdev, xorg or the kernel framebuffer driver? Any
pointer to the file I should patch would be much appreciated.

Many thanks in advance,

Gregoire