drm/i915: Prepare GEM for suspend earlier

In order to prepare the GPU for sleeping, we may want to submit commands
to it. This is a complicated process that may even require some swapping
in from shmemfs, if the GPU was in the wrong state. As such, we need to
do this preparation step synchronously before the rest of the system has
started to turn off (e.g. swapin fails if scsi is suspended).
Fortunately, we are provided with a such a hook, pm_ops.prepare().

v2: Compile cleanup
v3: Fewer asserts, fewer problems?

v4: Ville pointed out that in some circumstances (such as switching off
the overlay) the display code may issue a GPU request. This is
unexpected, and will result in us going to sleep with us believing the
GPU is still awake (though all user work has been saved). Add a comment
to remind our future selves of what trouble brews.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=106640
Testcase: igt/drv_suspend after igt/gem_tiled_swapping
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20180525092629.1456-1-chris@chris-wilson.co.uk
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>

drivers/gpu/drm/i915/i915_drv.c

@@ -1553,12 +1553,30 @@ static bool suspend_to_idle(struct drm_i915_private *dev_priv)
 	return false;
 }
 
+static int i915_drm_prepare(struct drm_device *dev)
+{
+	struct drm_i915_private *i915 = to_i915(dev);
+	int err;
+
+	/*
+	 * NB intel_display_suspend() may issue new requests after we've
+	 * ostensibly marked the GPU as ready-to-sleep here. We need to
+	 * split out that work and pull it forward so that after point,
+	 * the GPU is not woken again.
+	 */
+	err = i915_gem_suspend(i915);
+	if (err)
+		dev_err(&i915->drm.pdev->dev,
+			"GEM idle failed, suspend/resume might fail\n");
+
+	return err;
+}
+
 static int i915_drm_suspend(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = to_i915(dev);
 	struct pci_dev *pdev = dev_priv->drm.pdev;
 	pci_power_t opregion_target_state;
-	int error;
 
 	/* ignore lid events during suspend */
 	mutex_lock(&dev_priv->modeset_restore_lock);
@@ -1575,13 +1593,6 @@ static int i915_drm_suspend(struct drm_device *dev)
 
 	pci_save_state(pdev);
 
-	error = i915_gem_suspend(dev_priv);
-	if (error) {
-		dev_err(&pdev->dev,
-			"GEM idle failed, resume might fail\n");
-		goto out;
-	}
-
 	intel_display_suspend(dev);
 
 	intel_dp_mst_suspend(dev);
@@ -1609,10 +1620,9 @@ static int i915_drm_suspend(struct drm_device *dev)
 
 	intel_csr_ucode_suspend(dev_priv);
 
-out:
 	enable_rpm_wakeref_asserts(dev_priv);
 
-	return error;
+	return 0;
 }
 
 static int i915_drm_suspend_late(struct drm_device *dev, bool hibernation)
@@ -2081,6 +2091,22 @@ int i915_reset_engine(struct intel_engine_cs *engine, const char *msg)
 	return ret;
 }
 
+static int i915_pm_prepare(struct device *kdev)
+{
+	struct pci_dev *pdev = to_pci_dev(kdev);
+	struct drm_device *dev = pci_get_drvdata(pdev);
+
+	if (!dev) {
+		dev_err(kdev, "DRM not initialized, aborting suspend.\n");
+		return -ENODEV;
+	}
+
+	if (dev->switch_power_state == DRM_SWITCH_POWER_OFF)
+		return 0;
+
+	return i915_drm_prepare(dev);
+}
+
 static int i915_pm_suspend(struct device *kdev)
 {
 	struct pci_dev *pdev = to_pci_dev(kdev);
@@ -2731,6 +2757,7 @@ const struct dev_pm_ops i915_pm_ops = {
 	 * S0ix (via system suspend) and S3 event handlers [PMSG_SUSPEND,
 	 * PMSG_RESUME]
 	 */
+	.prepare = i915_pm_prepare,
 	.suspend = i915_pm_suspend,
 	.suspend_late = i915_pm_suspend_late,
 	.resume_early = i915_pm_resume_early,