drm/i915: Track the number of times we have woken the GPU up

By counting the number of times we have woken up, we have a very simple
means of defining an epoch, which will come in handy if we want to
perform deferred tasks at the end of an epoch (i.e. while we are going
to sleep) without imposing on the next activity cycle.

v2: No reason to specify precise number of bits here.
v3: Take Tvrtko's advice and reserve 0 as an invalid epoch.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180124113608.14909-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_debugfs.c

@@ -2717,7 +2717,8 @@ static int i915_runtime_pm_status(struct seq_file *m, void *unused)
 	if (!HAS_RUNTIME_PM(dev_priv))
 		seq_puts(m, "Runtime power management not supported\n");
 
-	seq_printf(m, "GPU idle: %s\n", yesno(!dev_priv->gt.awake));
+	seq_printf(m, "GPU idle: %s (epoch %u)\n",
+		   yesno(!dev_priv->gt.awake), dev_priv->gt.epoch);
 	seq_printf(m, "IRQs disabled: %s\n",
 		   yesno(!intel_irqs_enabled(dev_priv)));
 #ifdef CONFIG_PM
@@ -3150,8 +3151,8 @@ static int i915_engine_info(struct seq_file *m, void *unused)
 
 	intel_runtime_pm_get(dev_priv);
 
-	seq_printf(m, "GT awake? %s\n",
-		   yesno(dev_priv->gt.awake));
+	seq_printf(m, "GT awake? %s (epoch %u)\n",
+		   yesno(dev_priv->gt.awake), dev_priv->gt.epoch);
 	seq_printf(m, "Global active requests: %d\n",
 		   dev_priv->gt.active_requests);
 	seq_printf(m, "CS timestamp frequency: %u kHz\n",

drivers/gpu/drm/i915/i915_drv.h

@@ -2312,6 +2312,12 @@ struct drm_i915_private {
 		 */
 		bool awake;
 
+		/**
+		 * The number of times we have woken up.
+		 */
+		unsigned int epoch;
+#define I915_EPOCH_INVALID 0
+
 		/**
 		 * We leave the user IRQ off as much as possible,
 		 * but this means that requests will finish and never

drivers/gpu/drm/i915/i915_gem_request.c

@@ -274,6 +274,8 @@ static void mark_busy(struct drm_i915_private *i915)
 	intel_display_power_get(i915, POWER_DOMAIN_GT_IRQ);
 
 	i915->gt.awake = true;
+	if (unlikely(++i915->gt.epoch == 0)) /* keep 0 as invalid */
+		i915->gt.epoch = 1;
 
 	intel_enable_gt_powersave(i915);
 	i915_update_gfx_val(i915);