drm/i915/gen9_bc: Work around DMC bug zeroing power well requests

A DMC bug on GEN9 big core machines fails to restore the driver's
request bits for the PW1 and MISC_IO power wells after a DC5/6
entry->exit sequence. As a consequence the driver's subsequent check for
the enabled status of these power wells will fail, as the check
considers the power wells being enabled only if both the status and
request bits are set. To work around this borrow the request bits from
BIOS's own request register in which DMC forces on the request bits when
exiting from DC5/6.

This fixes a problem reported by Ramalingam, where HDCP init failed,
since PW1 reported itself as being disabled, while in reality it was
enabled.
Reported-by: Ramalingam C <ramalingam.c@intel.com>
Cc: Ramalingam C <ramalingam.c@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181109145822.15446-1-imre.deak@intel.com

drivers/gpu/drm/i915/intel_runtime_pm.c

@@ -493,11 +493,25 @@ static bool hsw_power_well_enabled(struct drm_i915_private *dev_priv,
 				   struct i915_power_well *power_well)
 {
 	const struct i915_power_well_regs *regs = power_well->desc->hsw.regs;
+	enum i915_power_well_id id = power_well->desc->id;
 	int pw_idx = power_well->desc->hsw.idx;
 	u32 mask = HSW_PWR_WELL_CTL_REQ(pw_idx) |
 		   HSW_PWR_WELL_CTL_STATE(pw_idx);
+	u32 val;
+
+	val = I915_READ(regs->driver);
+
+	/*
+	 * On GEN9 big core due to a DMC bug the driver's request bits for PW1
+	 * and the MISC_IO PW will be not restored, so check instead for the
+	 * BIOS's own request bits, which are forced-on for these power wells
+	 * when exiting DC5/6.
+	 */
+	if (IS_GEN9(dev_priv) && !IS_GEN9_LP(dev_priv) &&
+	    (id == SKL_DISP_PW_1 || id == SKL_DISP_PW_MISC_IO))
+		val |= I915_READ(regs->bios);
 
-	return (I915_READ(regs->driver) & mask) == mask;
+	return (val & mask) == mask;
 }
 
 static void assert_can_enable_dc9(struct drm_i915_private *dev_priv)