drm/i915: Convert sandybridge_pcode_*() to use intel_wait_for_register()

We want to replace the inline wait_for() with an out-of-line hybrid
busy/sleep wait_for() in the hopes of speeding up the communication wit
the PCode unit.

Indeed, on my i5-2500s, __gen6_update_ring_freq improves from
6,080,661ns to 8172ns.

v2: Missed using _fw variants for sandybridge_pcode_read()
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1467297225-21379-2-git-send-email-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/intel_pm.c

@@ -7623,46 +7623,59 @@ int sandybridge_pcode_read(struct drm_i915_private *dev_priv, u32 mbox, u32 *val
 {
 	WARN_ON(!mutex_is_locked(&dev_priv->rps.hw_lock));
 
-	if (I915_READ(GEN6_PCODE_MAILBOX) & GEN6_PCODE_READY) {
+	/* GEN6_PCODE_* are outside of the forcewake domain, we can
+	 * use te fw I915_READ variants to reduce the amount of work
+	 * required when reading/writing.
+	 */
+
+	if (I915_READ_FW(GEN6_PCODE_MAILBOX) & GEN6_PCODE_READY) {
 		DRM_DEBUG_DRIVER("warning: pcode (read) mailbox access failed\n");
 		return -EAGAIN;
 	}
 
-	I915_WRITE(GEN6_PCODE_DATA, *val);
-	I915_WRITE(GEN6_PCODE_DATA1, 0);
-	I915_WRITE(GEN6_PCODE_MAILBOX, GEN6_PCODE_READY | mbox);
+	I915_WRITE_FW(GEN6_PCODE_DATA, *val);
+	I915_WRITE_FW(GEN6_PCODE_DATA1, 0);
+	I915_WRITE_FW(GEN6_PCODE_MAILBOX, GEN6_PCODE_READY | mbox);
 
-	if (wait_for((I915_READ(GEN6_PCODE_MAILBOX) & GEN6_PCODE_READY) == 0,
-		     500)) {
+	if (intel_wait_for_register_fw(dev_priv,
+				       GEN6_PCODE_MAILBOX, GEN6_PCODE_READY, 0,
+				       500)) {
 		DRM_ERROR("timeout waiting for pcode read (%d) to finish\n", mbox);
 		return -ETIMEDOUT;
 	}
 
-	*val = I915_READ(GEN6_PCODE_DATA);
-	I915_WRITE(GEN6_PCODE_DATA, 0);
+	*val = I915_READ_FW(GEN6_PCODE_DATA);
+	I915_WRITE_FW(GEN6_PCODE_DATA, 0);
 
 	return 0;
 }
 
-int sandybridge_pcode_write(struct drm_i915_private *dev_priv, u32 mbox, u32 val)
+int sandybridge_pcode_write(struct drm_i915_private *dev_priv,
+			       u32 mbox, u32 val)
 {
 	WARN_ON(!mutex_is_locked(&dev_priv->rps.hw_lock));
 
-	if (I915_READ(GEN6_PCODE_MAILBOX) & GEN6_PCODE_READY) {
+	/* GEN6_PCODE_* are outside of the forcewake domain, we can
+	 * use te fw I915_READ variants to reduce the amount of work
+	 * required when reading/writing.
+	 */
+
+	if (I915_READ_FW(GEN6_PCODE_MAILBOX) & GEN6_PCODE_READY) {
 		DRM_DEBUG_DRIVER("warning: pcode (write) mailbox access failed\n");
 		return -EAGAIN;
 	}
 
-	I915_WRITE(GEN6_PCODE_DATA, val);
-	I915_WRITE(GEN6_PCODE_MAILBOX, GEN6_PCODE_READY | mbox);
+	I915_WRITE_FW(GEN6_PCODE_DATA, val);
+	I915_WRITE_FW(GEN6_PCODE_MAILBOX, GEN6_PCODE_READY | mbox);
 
-	if (wait_for((I915_READ(GEN6_PCODE_MAILBOX) & GEN6_PCODE_READY) == 0,
-		     500)) {
+	if (intel_wait_for_register_fw(dev_priv,
+				       GEN6_PCODE_MAILBOX, GEN6_PCODE_READY, 0,
+				       500)) {
 		DRM_ERROR("timeout waiting for pcode write (%d) to finish\n", mbox);
 		return -ETIMEDOUT;
 	}
 
-	I915_WRITE(GEN6_PCODE_DATA, 0);
+	I915_WRITE_FW(GEN6_PCODE_DATA, 0);
 
 	return 0;
 }