agp/intel-gtt: export the gtt pagetable iomapping

We need this because ppgtt page directory entries need to be in the
global gtt pagetable.

Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
Tested-by: Chris Wilson <chris@chris-wilson.co.uk>
Tested-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Reviewed-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/char/agp/intel-gtt.c

@@ -680,6 +680,7 @@ static int intel_gtt_init(void)
 		iounmap(intel_private.registers);
 		return -ENOMEM;
 	}
+	intel_private.base.gtt = intel_private.gtt;
 
 	global_cache_flush();   /* FIXME: ? */
 

include/drm/intel-gtt.h

@@ -17,6 +17,8 @@ const struct intel_gtt {
 	unsigned int do_idle_maps : 1;
 	/* Share the scratch page dma with ppgtts. */
 	dma_addr_t scratch_page_dma;
+	/* for ppgtt PDE access */
+	u32 __iomem *gtt;
 } *intel_gtt_get(void);
 
 void intel_gtt_chipset_flush(void);