drm/i915: Prefer setting PTE cache age to 3

We have conflicting benchmark data that suggest either age 0 or age 3 is
better. However, the earlier benchmark on which we based the switch to
age 0

(commit 0d8ff15e
Author: Ben Widawsky <benjamin.widawsky@intel.com>
Date:   Thu Jul 4 11:02:03 2013 -0700

    drm/i915/hsw: Set correct Haswell PTE encodings)

actually seems to prefer the default PTE encoding as age 3. Presumably,
this is in part due to the use of MOCS to override the PTE encodings
when appropriate.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=69870
Tested-by: mengmeng.meng@intel.com
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Reviewed-by: Eric Anholt <eric@anholt.net
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem_gtt.c

@@ -57,7 +57,9 @@ typedef gen8_gtt_pte_t gen8_ppgtt_pde_t;
 #define HSW_WB_LLC_AGE3			HSW_CACHEABILITY_CONTROL(0x2)
 #define HSW_WB_LLC_AGE0			HSW_CACHEABILITY_CONTROL(0x3)
 #define HSW_WB_ELLC_LLC_AGE0		HSW_CACHEABILITY_CONTROL(0xb)
+#define HSW_WB_ELLC_LLC_AGE3		HSW_CACHEABILITY_CONTROL(0x8)
 #define HSW_WT_ELLC_LLC_AGE0		HSW_CACHEABILITY_CONTROL(0x6)
+#define HSW_WT_ELLC_LLC_AGE3		HSW_CACHEABILITY_CONTROL(0x7)
 
 #define GEN8_PTES_PER_PAGE		(PAGE_SIZE / sizeof(gen8_gtt_pte_t))
 #define GEN8_PDES_PER_PAGE		(PAGE_SIZE / sizeof(gen8_ppgtt_pde_t))
@@ -185,10 +187,10 @@ static gen6_gtt_pte_t iris_pte_encode(dma_addr_t addr,
 	case I915_CACHE_NONE:
 		break;
 	case I915_CACHE_WT:
-		pte |= HSW_WT_ELLC_LLC_AGE0;
+		pte |= HSW_WT_ELLC_LLC_AGE3;
 		break;
 	default:
-		pte |= HSW_WB_ELLC_LLC_AGE0;
+		pte |= HSW_WB_ELLC_LLC_AGE3;
 		break;
 	}