drm/i915: support overclocking on Sandy Bridge

In some configuration, the PCU may allow us to overclock the GPU.
Check for this case and adjust the max frequency as appropriate.  Also
initialize the min/max frequencies to default values as indicated by
hardware.
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/i915_reg.h

@@ -3240,6 +3240,7 @@
 
 #define GEN6_PCODE_MAILBOX			0x138124
 #define   GEN6_PCODE_READY			(1<<31)
+#define   GEN6_READ_OC_PARAMS			0xc
 #define   GEN6_PCODE_WRITE_MIN_FREQ_TABLE	0x9
 #define GEN6_PCODE_DATA				0x138128
 

drivers/gpu/drm/i915/intel_display.c

@@ -6147,6 +6147,10 @@ void intel_init_emon(struct drm_device *dev)
 
 void gen6_enable_rps(struct drm_i915_private *dev_priv)
 {
+	u32 rp_state_cap = I915_READ(GEN6_RP_STATE_CAP);
+	u32 gt_perf_status = I915_READ(GEN6_GT_PERF_STATUS);
+	u32 pcu_mbox;
+	int cur_freq, min_freq, max_freq;
 	int i;
 
 	/* Here begins a magic sequence of register writes to enable
@@ -6218,6 +6222,29 @@ void gen6_enable_rps(struct drm_i915_private *dev_priv)
 		     500))
 		DRM_ERROR("timeout waiting for pcode mailbox to finish\n");
 
+	min_freq = (rp_state_cap & 0xff0000) >> 16;
+	max_freq = rp_state_cap & 0xff;
+	cur_freq = (gt_perf_status & 0xff00) >> 8;
+
+	/* Check for overclock support */
+	if (wait_for((I915_READ(GEN6_PCODE_MAILBOX) & GEN6_PCODE_READY) == 0,
+		     500))
+		DRM_ERROR("timeout waiting for pcode mailbox to become idle\n");
+	I915_WRITE(GEN6_PCODE_MAILBOX, GEN6_READ_OC_PARAMS);
+	pcu_mbox = I915_READ(GEN6_PCODE_DATA);
+	if (wait_for((I915_READ(GEN6_PCODE_MAILBOX) & GEN6_PCODE_READY) == 0,
+		     500))
+		DRM_ERROR("timeout waiting for pcode mailbox to finish\n");
+	if (pcu_mbox & (1<<31)) { /* OC supported */
+		max_freq = pcu_mbox & 0xff;
+		DRM_DEBUG_DRIVER("overclocking supported, adjusting frequency max to %dMHz\n", pcu_mbox * 100);
+	}
+
+	/* In units of 100MHz */
+	dev_priv->max_delay = max_freq;
+	dev_priv->min_delay = min_freq;
+	dev_priv->cur_delay = cur_freq;
+
 	/* requires MSI enabled */
 	I915_WRITE(GEN6_PMIER,
 		   GEN6_PM_MBOX_EVENT |