drm/i915: Keep user GGTT alive for a minimum of 250ms

Do not allow runtime pm autosuspend to remove userspace GGTT mmaps too
quickly. For example, igt sets the autosuspend delay to 0, and so we
immediately attempt to perform runtime suspend upon releasing the
wakeref. Unfortunately, that involves tearing down GGTT mmaps as they
require an active device.

Override the autosuspend for GGTT mmaps, by keeping the wakeref around
for 250ms after populating the PTE for a fresh mmap.

v2: Prefer refcount_t for its under/overflow error detection
v3: Flush the user runtime autosuspend prior to system system.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190527115114.13448-1-chris@chris-wilson.co.uk

1 files changed, 63 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/intel_wakeref.c b/drivers/gpu/drm/i915/intel_wakeref.c
index 91196d9612bb..c2dda5a375f0 100644
--- a/drivers/gpu/drm/i915/intel_wakeref.c
+++ b/drivers/gpu/drm/i915/intel_wakeref.c
@@ -73,3 +73,66 @@ void __intel_wakeref_init(struct intel_wakeref *wf, struct lock_class_key *key)
 	atomic_set(&wf->count, 0);
 	wf->wakeref = 0;
 }
+
+static void wakeref_auto_timeout(struct timer_list *t)
+{
+	struct intel_wakeref_auto *wf = from_timer(wf, t, timer);
+	intel_wakeref_t wakeref;
+	unsigned long flags;
+
+	if (!refcount_dec_and_lock_irqsave(&wf->count, &wf->lock, &flags))
+		return;
+
+	wakeref = fetch_and_zero(&wf->wakeref);
+	spin_unlock_irqrestore(&wf->lock, flags);
+
+	intel_runtime_pm_put(wf->i915, wakeref);
+}
+
+void intel_wakeref_auto_init(struct intel_wakeref_auto *wf,
+			     struct drm_i915_private *i915)
+{
+	spin_lock_init(&wf->lock);
+	timer_setup(&wf->timer, wakeref_auto_timeout, 0);
+	refcount_set(&wf->count, 0);
+	wf->wakeref = 0;
+	wf->i915 = i915;
+}
+
+void intel_wakeref_auto(struct intel_wakeref_auto *wf, unsigned long timeout)
+{
+	unsigned long flags;
+
+	if (!timeout) {
+		if (del_timer_sync(&wf->timer))
+			wakeref_auto_timeout(&wf->timer);
+		return;
+	}
+
+	/* Our mission is that we only extend an already active wakeref */
+	assert_rpm_wakelock_held(wf->i915);
+
+	if (!refcount_inc_not_zero(&wf->count)) {
+		spin_lock_irqsave(&wf->lock, flags);
+		if (!refcount_read(&wf->count)) {
+			GEM_BUG_ON(wf->wakeref);
+			wf->wakeref = intel_runtime_pm_get_if_in_use(wf->i915);
+		}
+		refcount_inc(&wf->count);
+		spin_unlock_irqrestore(&wf->lock, flags);
+	}
+
+	/*
+	 * If we extend a pending timer, we will only get a single timer
+	 * callback and so need to cancel the local inc by running the
+	 * elided callback to keep the wf->count balanced.
+	 */
+	if (mod_timer(&wf->timer, jiffies + timeout))
+		wakeref_auto_timeout(&wf->timer);
+}
+
+void intel_wakeref_auto_fini(struct intel_wakeref_auto *wf)
+{
+	intel_wakeref_auto(wf, 0);
+	GEM_BUG_ON(wf->wakeref);
+}