Comment # 8 on bug 57875 from Alex Deucher

(In reply to comment #7)
> Aw, of course thr R3xx_3D_Registers.pdf document doesn't document bit 24 of
> R300_GB_TILE_CONFIG, which supposedly contains the Z_EXTENDED flag...

That bit only exists on r5xx asics.  R3xx and r4xx don't have that bit.