Jessie on iMac G5 : advise needed about GPU setup

[Christophe De Natale <christophedenatale@orange.fr>]

Hello everybody,

I manage to post a step-by-step on Debian-wiki regarding install jessie on iMac G5 17 & 20 inches rev C but I need to achieve gpu setup.
Two machines are installed, it seems to work well but I’ve some doubts about ATI X600 adjustements and then I need to validate that all is right.
Sure, I read many topics, wikis, then mesa-utils tests were performed but my knowledge stops here and all these mechanisms about gpu are
complicated to understand for me.

I wrote three documents which contains glxinfo :
* at the fresh install (without non-free firmware + radeon driver)
* after install non-free (it breaks glxgears functionality)
* after downgrading mesa-lib in the previous version (to recover glxgears)
* according with the wiki, no try to use fglrx

So, I’ll be very grateful if somebody could to be a guide for me (all I need is to know how to choose a correct setup), I can send more informations about that.
And sorry for my bad english :-)

Cheers from France,

Christophe De Natale