drm/i915/skl: Implement enable/disable for Display C5 state.

This patch just implements the basic enable and disable
functions of DC5 state which is needed for both SKL and BXT.

Its important to load respective CSR program before calling
enable, which anyways will happen as CSR program is executed
during boot.

DC5 is a power saving state where hardware dynamically disables
power well 1 and the CDCLK PLL and saves the associated registers.

DC5 can be entered when software allows it, power well 2 is
disabled, and hardware detects that all pipes are disabled
or pipe A is enabled with PSR active.

Its better to configure display engine to have power well 2 disabled before
getting into DC5 enable function. Hence rpm framework will have to
ensure to check status of power well 2 before calling gen9_enable_dc5.

Rather dc5 entry criteria should be decided based on power well 2 status.
If disabled, then call gen9_enable_dc5.

v2: Replace HAS_ with IS_ check as per Daniel's review comments

v3: Cleared the bits dc5/dc6 enable of DC_STATE_EN register
before setting them as per Satheesh's review comments.

v4: call POSTING_READ for every write to a register to ensure that
its written immediately.

v5: Modified as per review comments from Imre.
- Squashed register definitions into this patch.
- Finetuned comments and functions.

v6:
Avoid redundant writes in gen9_set_dc_state_debugmask_memory_up function.

v7:
- Rebase to latest.
- Move all runtime PM functions defined in intel_display.c to
  intel_runtime_pm.c.

v8: Rebased to drm-intel-nightly. (Animesh)

Issue: VIZ-2819
Signed-off-by: A.Sunil Kamath <sunil.kamath@intel.com>
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Animesh Manna <animesh.manna@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_reg.h

@@ -7204,6 +7204,17 @@ enum skl_disp_power_wells {
 #define  DC_STATE_EN_UPTO_DC5		(1<<0)
 #define  DC_STATE_EN_DC9		(1<<3)
 
+/*
+* SKL DC
+*/
+#define  DC_STATE_EN			0x45504
+#define  DC_STATE_EN_UPTO_DC5		(1<<0)
+#define  DC_STATE_EN_UPTO_DC6		(2<<0)
+#define  DC_STATE_EN_UPTO_DC5_DC6_MASK   0x3
+
+#define  DC_STATE_DEBUG                  0x45520
+#define  DC_STATE_DEBUG_MASK_MEMORY_UP	(1<<1)
+
 /* Please see hsw_read_dcomp() and hsw_write_dcomp() before using this register,
  * since on HSW we can't write to it using I915_WRITE. */
 #define D_COMP_HSW			(MCHBAR_MIRROR_BASE_SNB + 0x5F0C)

drivers/gpu/drm/i915/intel_runtime_pm.c

@@ -419,14 +419,51 @@ void bxt_disable_dc9(struct drm_i915_private *dev_priv)
 	POSTING_READ(DC_STATE_EN);
 }
 
+static void gen9_set_dc_state_debugmask_memory_up(
+			struct drm_i915_private *dev_priv)
+{
+	uint32_t val;
+
+	/* The below bit doesn't need to be cleared ever afterwards */
+	val = I915_READ(DC_STATE_DEBUG);
+	if (!(val & DC_STATE_DEBUG_MASK_MEMORY_UP)) {
+		val |= DC_STATE_DEBUG_MASK_MEMORY_UP;
+		I915_WRITE(DC_STATE_DEBUG, val);
+		POSTING_READ(DC_STATE_DEBUG);
+	}
+}
+
 static void gen9_enable_dc5(struct drm_i915_private *dev_priv)
 {
-	/* TODO: Implementation to be done. */
+	struct drm_device *dev = dev_priv->dev;
+	uint32_t val;
+
+	WARN_ON(!IS_GEN9(dev));
+
+	DRM_DEBUG_KMS("Enabling DC5\n");
+
+	gen9_set_dc_state_debugmask_memory_up(dev_priv);
+
+	val = I915_READ(DC_STATE_EN);
+	val &= ~DC_STATE_EN_UPTO_DC5_DC6_MASK;
+	val |= DC_STATE_EN_UPTO_DC5;
+	I915_WRITE(DC_STATE_EN, val);
+	POSTING_READ(DC_STATE_EN);
 }
 
 static void gen9_disable_dc5(struct drm_i915_private *dev_priv)
 {
-	/* TODO: Implementation to be done. */
+	struct drm_device *dev = dev_priv->dev;
+	uint32_t val;
+
+	WARN_ON(!IS_GEN9(dev));
+
+	DRM_DEBUG_KMS("Disabling DC5\n");
+
+	val = I915_READ(DC_STATE_EN);
+	val &= ~DC_STATE_EN_UPTO_DC5;
+	I915_WRITE(DC_STATE_EN, val);
+	POSTING_READ(DC_STATE_EN);
 }
 
 static void skl_set_power_well(struct drm_i915_private *dev_priv,