+static uint32_t get_allowed_dc_mask(const struct drm_i915_private *dev_priv,
+ int enable_dc)
+{
+ uint32_t mask;
+ int requested_dc;
+ int max_dc;
+
+ if (IS_SKYLAKE(dev_priv) || IS_KABYLAKE(dev_priv)) {
+ max_dc = 2;
+ mask = 0;
+ } else if (IS_BROXTON(dev_priv)) {
+ max_dc = 1;
+ /*
+ * DC9 has a separate HW flow from the rest of the DC states,
+ * not depending on the DMC firmware. It's needed by system
+ * suspend/resume, so allow it unconditionally.
+ */
+ mask = DC_STATE_EN_DC9;
+ } else {
+ max_dc = 0;
+ mask = 0;
+ }
+
+ if (!i915.disable_power_well)
+ max_dc = 0;
+
+ if (enable_dc >= 0 && enable_dc <= max_dc) {
+ requested_dc = enable_dc;
+ } else if (enable_dc == -1) {
+ requested_dc = max_dc;
+ } else if (enable_dc > max_dc && enable_dc <= 2) {
+ DRM_DEBUG_KMS("Adjusting requested max DC state (%d->%d)\n",
+ enable_dc, max_dc);
+ requested_dc = max_dc;
+ } else {
+ DRM_ERROR("Unexpected value for enable_dc (%d)\n", enable_dc);
+ requested_dc = max_dc;
+ }
+
+ if (requested_dc > 1)
+ mask |= DC_STATE_EN_UPTO_DC6;
+ if (requested_dc > 0)
+ mask |= DC_STATE_EN_UPTO_DC5;
+
+ DRM_DEBUG_KMS("Allowed DC state mask %02x\n", mask);
+
+ return mask;
+}
+