drm/i915/bdw: don't try to check IPS state on BDW v2

According to Art, we don't have a way to read back the state reliably at
runtime, through the control reg or the mailbox, at least not without risking
disabling it again.  So drop the readout and checking on BDW.

v2: drop TODO comment (Paulo)
    move POSTING_READ of control reg under HSW branch in disable (Paulo)
    always report IPS as enabled on BDW (Paulo)

References: https://bugs.freedesktop.org/show_bug.cgi?id=71906
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_debugfs.c

@@ -1357,7 +1357,7 @@ static int i915_ips_status(struct seq_file *m, void *unused)
 		return 0;
 	}
 
-	if (I915_READ(IPS_CTL) & IPS_ENABLE)
+	if (IS_BROADWELL(dev) || I915_READ(IPS_CTL) & IPS_ENABLE)
 		seq_puts(m, "enabled\n");
 	else
 		seq_puts(m, "disabled\n");

drivers/gpu/drm/i915/intel_display.c

@@ -3433,9 +3433,8 @@ void hsw_enable_ips(struct intel_crtc *crtc)
 		mutex_unlock(&dev_priv->rps.hw_lock);
 		/* Quoting Art Runyan: "its not safe to expect any particular
 		 * value in IPS_CTL bit 31 after enabling IPS through the
-		 * mailbox." Therefore we need to defer waiting on the state
-		 * change.
-		 * TODO: need to fix this for state checker
+		 * mailbox." Moreover, the mailbox may return a bogus state,
+		 * so we need to just enable it and continue on.
 		 */
 	} else {
 		I915_WRITE(IPS_CTL, IPS_ENABLE);
@@ -3462,9 +3461,10 @@ void hsw_disable_ips(struct intel_crtc *crtc)
 		mutex_lock(&dev_priv->rps.hw_lock);
 		WARN_ON(sandybridge_pcode_write(dev_priv, DISPLAY_IPS_CONTROL, 0));
 		mutex_unlock(&dev_priv->rps.hw_lock);
-	} else
+	} else {
 		I915_WRITE(IPS_CTL, 0);
-	POSTING_READ(IPS_CTL);
+		POSTING_READ(IPS_CTL);
+	}
 
 	/* We need to wait for a vblank before we can disable the plane. */
 	intel_wait_for_vblank(dev, crtc->pipe);
@@ -7006,8 +7006,9 @@ static bool haswell_get_pipe_config(struct intel_crtc *crtc,
 	if (intel_display_power_enabled(dev, pfit_domain))
 		ironlake_get_pfit_config(crtc, pipe_config);
 
-	pipe_config->ips_enabled = hsw_crtc_supports_ips(crtc) &&
-				   (I915_READ(IPS_CTL) & IPS_ENABLE);
+	if (IS_HASWELL(dev))
+		pipe_config->ips_enabled = hsw_crtc_supports_ips(crtc) &&
+			(I915_READ(IPS_CTL) & IPS_ENABLE);
 
 	pipe_config->pixel_multiplier = 1;
 
@@ -9336,7 +9337,9 @@ intel_pipe_config_compare(struct drm_device *dev,
 		PIPE_CONF_CHECK_I(pch_pfit.size);
 	}
 
-	PIPE_CONF_CHECK_I(ips_enabled);
+	/* BDW+ don't expose a synchronous way to read the state */
+	if (IS_HASWELL(dev))
+		PIPE_CONF_CHECK_I(ips_enabled);
 
 	PIPE_CONF_CHECK_I(double_wide);