drm/i915/gen9: Reset secondary power well requests left on by DMC/KVMR

DMC forces on power well 1 and the misc IO power well by setting the
corresponding request bits both in the BIOS and the DEBUG power well
request registers. This is somewhat unexpected since the firmware should
really just save and restore state but not alter it. We also depend on
being able to disable power well 1, and the misc IO power well before
entering S3/S4 on BXT and SKL or entering DC9 on BXT. To fix this make
sure these request bits are cleared whenever we want to disable the
given power wells.

On SKL there is another twist where the firmware also clears the power
well 1 request bit in HSW_POWER_WELL_DRIVER (but not that of the misc IO
power well). This happens to not cause a problem due to the forced-on
request bits in the other request registers.

I've filed a bug about all this, but fixing that may take a while and
having this sanity check in place makes sense even for future firmware
versions.

At the same time also check the KVMR request bits. I haven't seen this
being altered, but we don't expect any request bits in here either, so
sanitize this register as well.

v2:
- Apply the workaround on SKL as well. I noticed the related failure
  from the CI report, later Patrik also reported seeing it on his
  machine.

CC: Patrik Jakobsson <patrik.jakobsson@linux.intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Patrik Jakobsson <patrik.jakobsson@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1459851965-6137-1-git-send-email-imre.deak@intel.com

drivers/gpu/drm/i915/intel_runtime_pm.c

@@ -630,6 +630,44 @@ void skl_disable_dc6(struct drm_i915_private *dev_priv)
 	gen9_set_dc_state(dev_priv, DC_STATE_DISABLE);
 }
 
+static void
+gen9_sanitize_power_well_requests(struct drm_i915_private *dev_priv,
+				  struct i915_power_well *power_well)
+{
+	enum skl_disp_power_wells power_well_id = power_well->data;
+	u32 val;
+	u32 mask;
+
+	mask = SKL_POWER_WELL_REQ(power_well_id);
+
+	val = I915_READ(HSW_PWR_WELL_KVMR);
+	if (WARN_ONCE(val & mask, "Clearing unexpected KVMR request for %s\n",
+		      power_well->name))
+		I915_WRITE(HSW_PWR_WELL_KVMR, val & ~mask);
+
+	val = I915_READ(HSW_PWR_WELL_BIOS);
+	val |= I915_READ(HSW_PWR_WELL_DEBUG);
+
+	if (!(val & mask))
+		return;
+
+	/*
+	 * DMC is known to force on the request bits for power well 1 on SKL
+	 * and BXT and the misc IO power well on SKL but we don't expect any
+	 * other request bits to be set, so WARN for those.
+	 */
+	if (power_well_id == SKL_DISP_PW_1 ||
+	    (IS_SKYLAKE(dev_priv) && power_well_id == SKL_DISP_PW_MISC_IO))
+		DRM_DEBUG_DRIVER("Clearing auxiliary requests for %s forced on "
+				 "by DMC\n", power_well->name);
+	else
+		WARN_ONCE(1, "Clearing unexpected auxiliary requests for %s\n",
+			  power_well->name);
+
+	I915_WRITE(HSW_PWR_WELL_BIOS, val & ~mask);
+	I915_WRITE(HSW_PWR_WELL_DEBUG, val & ~mask);
+}
+
 static void skl_set_power_well(struct drm_i915_private *dev_priv,
 			struct i915_power_well *power_well, bool enable)
 {
@@ -696,6 +734,9 @@ static void skl_set_power_well(struct drm_i915_private *dev_priv,
 			POSTING_READ(HSW_PWR_WELL_DRIVER);
 			DRM_DEBUG_KMS("Disabling %s\n", power_well->name);
 		}
+
+		if (IS_SKYLAKE(dev_priv) || IS_BROXTON(dev_priv))
+			gen9_sanitize_power_well_requests(dev_priv, power_well);
 	}
 
 	if (check_fuse_status) {