drm/i915: reintroduce VLV/CHV PFI programming power domain workaround

There are still cases on these platforms where an attempt is made to
configure the CDCLK while the power domain is off, like when coming back
from a suspend.  So the workaround below is still needed.

This effectively reverts commit 63ff30442519 ("drm/i915: Nuke the
VLV/CHV PFI programming power domain workaround").

Cc: stable@vger.kernel.org
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=101517
Suggested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/20170628210605.4994-1-krisman@collabora.co.uk
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

drivers/gpu/drm/i915/intel_cdclk.c

@@ -491,6 +491,14 @@ static void vlv_set_cdclk(struct drm_i915_private *dev_priv,
 	int cdclk = cdclk_state->cdclk;
 	u32 val, cmd;
 
+	/* There are cases where we can end up here with power domains
+	 * off and a CDCLK frequency other than the minimum, like when
+	 * issuing a modeset without actually changing any display after
+	 * a system suspend.  So grab the PIPE-A domain, which covers
+	 * the HW blocks needed for the following programming.
+	 */
+	intel_display_power_get(dev_priv, POWER_DOMAIN_PIPE_A);
+
 	if (cdclk >= 320000) /* jump to highest voltage for 400MHz too */
 		cmd = 2;
 	else if (cdclk == 266667)
@@ -549,6 +557,8 @@ static void vlv_set_cdclk(struct drm_i915_private *dev_priv,
 	intel_update_cdclk(dev_priv);
 
 	vlv_program_pfi_credits(dev_priv);
+
+	intel_display_power_put(dev_priv, POWER_DOMAIN_PIPE_A);
 }
 
 static void chv_set_cdclk(struct drm_i915_private *dev_priv,
@@ -568,6 +578,14 @@ static void chv_set_cdclk(struct drm_i915_private *dev_priv,
 		return;
 	}
 
+	/* There are cases where we can end up here with power domains
+	 * off and a CDCLK frequency other than the minimum, like when
+	 * issuing a modeset without actually changing any display after
+	 * a system suspend.  So grab the PIPE-A domain, which covers
+	 * the HW blocks needed for the following programming.
+	 */
+	intel_display_power_get(dev_priv, POWER_DOMAIN_PIPE_A);
+
 	/*
 	 * Specs are full of misinformation, but testing on actual
 	 * hardware has shown that we just need to write the desired
@@ -590,6 +608,8 @@ static void chv_set_cdclk(struct drm_i915_private *dev_priv,
 	intel_update_cdclk(dev_priv);
 
 	vlv_program_pfi_credits(dev_priv);
+
+	intel_display_power_put(dev_priv, POWER_DOMAIN_PIPE_A);
 }
 
 static int bdw_calc_cdclk(int max_pixclk)