drm/i915/bxt: reserve space for RC6 in the the GuC WOPCM

This patch resizes the GuC WOPCM (specifically on BXT)
so that the GuC and RC6 memory spaces do not overlap.

v2:
    Made calculation of WOPCM size into a separate function,
    so that it's consistent between the firmware size-check
    and the register-programming operations [Dave Gordon].

Issue: https://jira01.devtools.intel.com/browse/VIZ-6638
Signed-off-by: Peter Antoine <peter.antoine@intel.com>
Signed-off-by: Dave Gordon <david.s.gordon@intel.com>
Reviewed-by: Nick Hoath <nicholas.hoath@intel.com>
Tested-by: Nick Hoath <nicholas.hoath@intel.com>
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1463494365-26330-1-git-send-email-david.s.gordon@intel.com
diff --git a/drivers/gpu/drm/i915/i915_guc_reg.h b/drivers/gpu/drm/i915/i915_guc_reg.h
index 80786d9..cf5a65b 100644
--- a/drivers/gpu/drm/i915/i915_guc_reg.h
+++ b/drivers/gpu/drm/i915/i915_guc_reg.h
@@ -67,11 +67,11 @@
 #define   GUC_WOPCM_OFFSET_VALUE	  0x80000	/* 512KB */
 #define GUC_MAX_IDLE_COUNT		_MMIO(0xC3E4)
 
+/* Defines WOPCM space available to GuC firmware */
 #define GUC_WOPCM_SIZE			_MMIO(0xc050)
-#define   GUC_WOPCM_SIZE_VALUE  	  (0x80 << 12)	/* 512KB */
-
 /* GuC addresses below GUC_WOPCM_TOP don't map through the GTT */
-#define	GUC_WOPCM_TOP			(GUC_WOPCM_SIZE_VALUE)
+#define   GUC_WOPCM_TOP			  (0x80 << 12)	/* 512KB */
+#define   BXT_GUC_WOPCM_RC6_RESERVED	  (0x10 << 12)	/* 64KB  */
 
 #define GEN8_GT_PM_CONFIG		_MMIO(0x138140)
 #define GEN9LP_GT_PM_CONFIG		_MMIO(0x138140)