drm/i915/icl: Set graphics mode register for gen11

This patch clears a single bit. The bit is 0 by default but expected
not to be set. Explicitly clearing the bit in this patch is intended
to indicate some thinking has occurred, and that we want this bit
cleared and we are not just excepting the default value.

We also stop setting GFX_RUN_LIST_ENABLE, which is correct since that
bit is gone.

v2 (from Paulo): fix indentation.
v3: Changed GEN check to >= 11. Corrected author name.
v4 (from Paulo): improve commit message (Daniele).
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: Kelvin Gardiner <kelvin.gardiner@intel.com>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180130134918.32283-9-paulo.r.zanoni@intel.com

drivers/gpu/drm/i915/i915_reg.h

@@ -2592,6 +2592,8 @@ enum i915_power_well_id {
 #define   GFX_FORWARD_VBLANK_ALWAYS	(1<<5)
 #define   GFX_FORWARD_VBLANK_COND	(2<<5)
 
+#define   GEN11_GFX_DISABLE_LEGACY_MODE	(1<<3)
+
 #define VLV_DISPLAY_BASE 0x180000
 #define VLV_MIPI_BASE VLV_DISPLAY_BASE
 #define BXT_MIPI_BASE 0x60000

drivers/gpu/drm/i915/intel_lrc.c

@@ -1443,8 +1443,22 @@ static void enable_execlists(struct intel_engine_cs *engine)
 	struct drm_i915_private *dev_priv = engine->i915;
 
 	I915_WRITE(RING_HWSTAM(engine->mmio_base), 0xffffffff);
-	I915_WRITE(RING_MODE_GEN7(engine),
-		   _MASKED_BIT_ENABLE(GFX_RUN_LIST_ENABLE));
+
+	/*
+	 * Make sure we're not enabling the new 12-deep CSB
+	 * FIFO as that requires a slightly updated handling
+	 * in the ctx switch irq. Since we're currently only
+	 * using only 2 elements of the enhanced execlists the
+	 * deeper FIFO it's not needed and it's not worth adding
+	 * more statements to the irq handler to support it.
+	 */
+	if (INTEL_GEN(dev_priv) >= 11)
+		I915_WRITE(RING_MODE_GEN7(engine),
+			   _MASKED_BIT_DISABLE(GEN11_GFX_DISABLE_LEGACY_MODE));
+	else
+		I915_WRITE(RING_MODE_GEN7(engine),
+			   _MASKED_BIT_ENABLE(GFX_RUN_LIST_ENABLE));
+
 	I915_WRITE(RING_HWS_PGA(engine->mmio_base),
 		   engine->status_page.ggtt_offset);
 	POSTING_READ(RING_HWS_PGA(engine->mmio_base));