Radeon MC setup cleanup

[Maciej Cencora]

Hi all,

I'm trying to understand and cleanup MC setup in Radeon DDX driver. 
Currently it's overcomplicated and sometimes unreliable.

That's how I understand how MC should be setup. Please check if I 
understand it correctly.

When DRI is disabled, fb/agp locations should not change during whole 
session (even when doing VT switch) so there is no need to save/restore 
them.

Below I describe the cases when DRI is enabled.
-- User starts the machine --
Initial reg values are set by BIOS.

-- User starts X --
1. Store regs in info->SavedReg.
2. Init DRI (it sets new values to fb/agp location regs).
3. Save new fb/agp location values to info->ModeReg.

-- User calls LeaveVT --
Restore regs from info->SavedReg and do the rest of LeaveVT.

-- User backs to X (EnterVT) --
Restore regs from info->ModeReg and do the rest of EnterVT.

-- User closes X -- (that case is similar to LeaveVT)
Restore regs from info->SavedReg and do the rest of LeaveVT.


Regards,
Maciej Cencora