drm/i915/ibx: Ensure the HW is powered during PLL HW readout

The assumption when adding the intel_display_power_is_enabled() checks
was that if it returns success the power can't be turned off afterwards
during the HW access, which is guaranteed by modeset locks. This isn't
always true, so make sure we hold a dedicated reference for the time of
the access.
Signed-off-by: NImre Deak <imre.deak@intel.com>
Reviewed-by: NMika Kuoppala <mika.kuoppala@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1455296121-4742-4-git-send-email-imre.deak@intel.com
(cherry picked from commit 12fda387)
Signed-off-by: NJani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/intel_display.c

@@ -13659,7 +13659,7 @@ static bool ibx_pch_dpll_get_hw_state(struct drm_i915_private *dev_priv,
 {
 	uint32_t val;
 
-	if (!intel_display_power_is_enabled(dev_priv, POWER_DOMAIN_PLLS))
+	if (!intel_display_power_get_if_enabled(dev_priv, POWER_DOMAIN_PLLS))
 		return false;
 
 	val = I915_READ(PCH_DPLL(pll->id));
@@ -13667,6 +13667,8 @@ static bool ibx_pch_dpll_get_hw_state(struct drm_i915_private *dev_priv,
 	hw_state->fp0 = I915_READ(PCH_FP0(pll->id));
 	hw_state->fp1 = I915_READ(PCH_FP1(pll->id));
 
+	intel_display_power_put(dev_priv, POWER_DOMAIN_PLLS);
+
 	return val & DPLL_VCO_ENABLE;
 }