drm/i915/gen9: Add boot parameter for disabling DC6

v2: Use _unsafe (Jani)
v3: Allow specifying specific DC-states instead of just DC6 (Imre)

Signed-off-by: Patrik Jakobsson <patrik.jakobsson@linux.intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1447682467-6237-3-git-send-email-patrik.jakobsson@linux.intel.com

drivers/gpu/drm/i915/i915_drv.h

@@ -2642,6 +2642,7 @@ struct i915_params {
 	int panel_use_ssc;
 	int vbt_sdvo_panel_type;
 	int enable_rc6;
+	int enable_dc;
 	int enable_fbc;
 	int enable_ppgtt;
 	int enable_execlists;

drivers/gpu/drm/i915/i915_params.c

@@ -32,6 +32,7 @@ struct i915_params i915 __read_mostly = {
 	.panel_use_ssc = -1,
 	.vbt_sdvo_panel_type = -1,
 	.enable_rc6 = -1,
+	.enable_dc = -1,
 	.enable_fbc = -1,
 	.enable_execlists = -1,
 	.enable_hangcheck = true,
@@ -79,6 +80,11 @@ MODULE_PARM_DESC(enable_rc6,
 	"For example, 3 would enable rc6 and deep rc6, and 7 would enable everything. "
 	"default: -1 (use per-chip default)");
 
+module_param_named_unsafe(enable_dc, i915.enable_dc, int, 0400);
+MODULE_PARM_DESC(enable_dc,
+	"Enable power-saving display C-states. "
+	"(-1=auto [default]; 0=disable; 1=up to DC5; 2=up to DC6)");
+
 module_param_named_unsafe(enable_fbc, i915.enable_fbc, int, 0600);
 MODULE_PARM_DESC(enable_fbc,
 	"Enable frame buffer compression for power savings "

drivers/gpu/drm/i915/intel_runtime_pm.c

@@ -417,6 +417,11 @@ static void gen9_set_dc_state(struct drm_i915_private *dev_priv, uint32_t state)
 
 	WARN_ON_ONCE(state & ~mask);
 
+	if (i915.enable_dc == 0)
+		state = DC_STATE_DISABLE;
+	else if (i915.enable_dc == 1 && state > DC_STATE_EN_UPTO_DC5)
+		state = DC_STATE_EN_UPTO_DC5;
+
 	if (state & DC_STATE_EN_UPTO_DC5_DC6_MASK)
 		gen9_set_dc_state_debugmask_memory_up(dev_priv);
 
@@ -525,7 +530,9 @@ static void assert_can_disable_dc6(struct drm_i915_private *dev_priv)
 static void gen9_disable_dc5_dc6(struct drm_i915_private *dev_priv)
 {
 	assert_can_disable_dc5(dev_priv);
-	assert_can_disable_dc6(dev_priv);
+
+	if (IS_SKYLAKE(dev_priv) && i915.enable_dc != 0 && i915.enable_dc != 1)
+		assert_can_disable_dc6(dev_priv);
 
 	gen9_set_dc_state(dev_priv, DC_STATE_DISABLE);
 }
@@ -712,7 +719,7 @@ static void gen9_dc_off_power_well_enable(struct drm_i915_private *dev_priv,
 static void gen9_dc_off_power_well_disable(struct drm_i915_private *dev_priv,
 					   struct i915_power_well *power_well)
 {
-	if (IS_SKYLAKE(dev_priv))
+	if (IS_SKYLAKE(dev_priv) && i915.enable_dc != 0 && i915.enable_dc != 1)
 		skl_enable_dc6(dev_priv);
 	else
 		gen9_enable_dc5(dev_priv);
@@ -724,7 +731,8 @@ static void gen9_dc_off_power_well_sync_hw(struct drm_i915_private *dev_priv,
 	if (power_well->count > 0) {
 		gen9_set_dc_state(dev_priv, DC_STATE_DISABLE);
 	} else {
-		if (IS_SKYLAKE(dev_priv))
+		if (IS_SKYLAKE(dev_priv) && i915.enable_dc != 0 &&
+		    i915.enable_dc != 1)
 			gen9_set_dc_state(dev_priv, DC_STATE_EN_UPTO_DC6);
 		else
 			gen9_set_dc_state(dev_priv, DC_STATE_EN_UPTO_DC5);