drm/i915: Set up the documented clock gating on Sandybridge and Ironlake.

Signed-off-by: NEric Anholt <eric@anholt.net>

drivers/gpu/drm/i915/i915_reg.h

@@ -2176,6 +2176,14 @@
 #define DISPLAY_PORT_PLL_BIOS_1         0x46010
 #define DISPLAY_PORT_PLL_BIOS_2         0x46014
 
+#define PCH_DSPCLK_GATE_D	0x42020
+# define DPFDUNIT_CLOCK_GATE_DISABLE		(1 << 7)
+# define DPARBUNIT_CLOCK_GATE_DISABLE		(1 << 5)
+
+#define PCH_3DCGDIS0		0x46020
+# define MARIUNIT_CLOCK_GATE_DISABLE		(1 << 18)
+# define SVSMUNIT_CLOCK_GATE_DISABLE		(1 << 1)
+
 #define FDI_PLL_FREQ_CTL        0x46030
 #define  FDI_PLL_FREQ_CHANGE_REQUEST    (1<<24)
 #define  FDI_PLL_FREQ_LOCK_LIMIT_MASK   0xfff00

drivers/gpu/drm/i915/intel_display.c

@@ -4717,6 +4717,20 @@ void intel_init_clock_gating(struct drm_device *dev)
 	 * specs, but enable as much else as we can.
 	 */
 	if (HAS_PCH_SPLIT(dev)) {
+		uint32_t dspclk_gate = VRHUNIT_CLOCK_GATE_DISABLE;
+
+		if (IS_IRONLAKE(dev)) {
+			/* Required for FBC */
+			dspclk_gate |= DPFDUNIT_CLOCK_GATE_DISABLE;
+			/* Required for CxSR */
+			dspclk_gate |= DPARBUNIT_CLOCK_GATE_DISABLE;
+
+			I915_WRITE(PCH_3DCGDIS0,
+				   MARIUNIT_CLOCK_GATE_DISABLE |
+				   SVSMUNIT_CLOCK_GATE_DISABLE);
+		}
+
+		I915_WRITE(PCH_DSPCLK_GATE_D, dspclk_gate);
 		return;
 	} else if (IS_G4X(dev)) {
 		uint32_t dspclk_gate;