drm/i915/debugfs: Add i915_hpd_storm_ctl

This adds a file in i915's debugfs directory that allows userspace to
manually control HPD storm detection. This is mainly for hotplugging
tests, where we might want to test HPD storm functionality or disable
storm detection to speed up hotplugging tests without breaking anything.

Changes since v1:
- Make HPD storm interval configurable
- Misc code cleanup

Signed-off-by: Lyude <lyude@redhat.com>
Acked-by: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Tomeu Vizoso <tomeu@tomeuvizoso.net>

drivers/gpu/drm/i915/i915_debugfs.c

@@ -4653,6 +4653,81 @@ static int i915_forcewake_create(struct dentry *root, struct drm_minor *minor)
 	return drm_add_fake_info_node(minor, ent, &i915_forcewake_fops);
 }
 
+static int i915_hpd_storm_ctl_show(struct seq_file *m, void *data)
+{
+	struct drm_i915_private *dev_priv = m->private;
+	struct i915_hotplug *hotplug = &dev_priv->hotplug;
+
+	seq_printf(m, "Threshold: %d\n", hotplug->hpd_storm_threshold);
+	seq_printf(m, "Detected: %s\n",
+		   yesno(delayed_work_pending(&hotplug->reenable_work)));
+
+	return 0;
+}
+
+static ssize_t i915_hpd_storm_ctl_write(struct file *file,
+					const char __user *ubuf, size_t len,
+					loff_t *offp)
+{
+	struct seq_file *m = file->private_data;
+	struct drm_i915_private *dev_priv = m->private;
+	struct i915_hotplug *hotplug = &dev_priv->hotplug;
+	unsigned int new_threshold;
+	int i;
+	char *newline;
+	char tmp[16];
+
+	if (len >= sizeof(tmp))
+		return -EINVAL;
+
+	if (copy_from_user(tmp, ubuf, len))
+		return -EFAULT;
+
+	tmp[len] = '\0';
+
+	/* Strip newline, if any */
+	newline = strchr(tmp, '\n');
+	if (newline)
+		*newline = '\0';
+
+	if (strcmp(tmp, "reset") == 0)
+		new_threshold = HPD_STORM_DEFAULT_THRESHOLD;
+	else if (kstrtouint(tmp, 10, &new_threshold) != 0)
+		return -EINVAL;
+
+	if (new_threshold > 0)
+		DRM_DEBUG_KMS("Setting HPD storm detection threshold to %d\n",
+			      new_threshold);
+	else
+		DRM_DEBUG_KMS("Disabling HPD storm detection\n");
+
+	spin_lock_irq(&dev_priv->irq_lock);
+	hotplug->hpd_storm_threshold = new_threshold;
+	/* Reset the HPD storm stats so we don't accidentally trigger a storm */
+	for_each_hpd_pin(i)
+		hotplug->stats[i].count = 0;
+	spin_unlock_irq(&dev_priv->irq_lock);
+
+	/* Re-enable hpd immediately if we were in an irq storm */
+	flush_delayed_work(&dev_priv->hotplug.reenable_work);
+
+	return len;
+}
+
+static int i915_hpd_storm_ctl_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, i915_hpd_storm_ctl_show, inode->i_private);
+}
+
+static const struct file_operations i915_hpd_storm_ctl_fops = {
+	.owner = THIS_MODULE,
+	.open = i915_hpd_storm_ctl_open,
+	.read = seq_read,
+	.llseek = seq_lseek,
+	.release = single_release,
+	.write = i915_hpd_storm_ctl_write
+};
+
 static int i915_debugfs_create(struct dentry *root,
 			       struct drm_minor *minor,
 			       const char *name,
@@ -4746,7 +4821,8 @@ static const struct i915_debugfs_files {
 	{"i915_dp_test_data", &i915_displayport_test_data_fops},
 	{"i915_dp_test_type", &i915_displayport_test_type_fops},
 	{"i915_dp_test_active", &i915_displayport_test_active_fops},
-	{"i915_guc_log_control", &i915_guc_log_control_fops}
+	{"i915_guc_log_control", &i915_guc_log_control_fops},
+	{"i915_hpd_storm_ctl", &i915_hpd_storm_ctl_fops}
 };
 
 int i915_debugfs_register(struct drm_i915_private *dev_priv)

drivers/gpu/drm/i915/i915_drv.c

@@ -827,6 +827,7 @@ static int i915_driver_init_early(struct drm_i915_private *dev_priv,
 	spin_lock_init(&dev_priv->gpu_error.lock);
 	mutex_init(&dev_priv->backlight_lock);
 	spin_lock_init(&dev_priv->uncore.lock);
+
 	spin_lock_init(&dev_priv->mm.object_stat_lock);
 	spin_lock_init(&dev_priv->mmio_flip_lock);
 	spin_lock_init(&dev_priv->wm.dsparb_lock);

drivers/gpu/drm/i915/i915_drv.h

@@ -384,6 +384,8 @@ enum hpd_pin {
 #define for_each_hpd_pin(__pin) \
 	for ((__pin) = (HPD_NONE + 1); (__pin) < HPD_NUM_PINS; (__pin)++)
 
+#define HPD_STORM_DEFAULT_THRESHOLD 5
+
 struct i915_hotplug {
 	struct work_struct hotplug_work;
 
@@ -407,6 +409,8 @@ struct i915_hotplug {
 	struct work_struct poll_init_work;
 	bool poll_enabled;
 
+	unsigned int hpd_storm_threshold;
+
 	/*
 	 * if we get a HPD irq from DP and a HPD irq from non-DP
 	 * the non-DP HPD could block the workqueue on a mode config

drivers/gpu/drm/i915/i915_irq.c

@@ -4277,6 +4277,8 @@ void intel_irq_init(struct drm_i915_private *dev_priv)
 	if (!IS_GEN2(dev_priv))
 		dev->vblank_disable_immediate = true;
 
+	dev_priv->hotplug.hpd_storm_threshold = HPD_STORM_DEFAULT_THRESHOLD;
+
 	dev->driver->get_vblank_timestamp = i915_get_vblank_timestamp;
 	dev->driver->get_scanout_position = i915_get_crtc_scanoutpos;
 

drivers/gpu/drm/i915/intel_hotplug.c

@@ -100,7 +100,6 @@ bool intel_hpd_pin_to_port(enum hpd_pin pin, enum port *port)
 }
 
 #define HPD_STORM_DETECT_PERIOD		1000
-#define HPD_STORM_THRESHOLD		5
 #define HPD_STORM_REENABLE_DELAY	(2 * 60 * 1000)
 
 /**
@@ -112,9 +111,13 @@ bool intel_hpd_pin_to_port(enum hpd_pin pin, enum port *port)
  * storms. Only the pin specific stats and state are changed, the caller is
  * responsible for further action.
  *
- * @HPD_STORM_THRESHOLD irqs are allowed within @HPD_STORM_DETECT_PERIOD ms,
- * otherwise it's considered an irq storm, and the irq state is set to
- * @HPD_MARK_DISABLED.
+ * The number of irqs that are allowed within @HPD_STORM_DETECT_PERIOD is
+ * stored in @dev_priv->hotplug.hpd_storm_threshold which defaults to
+ * @HPD_STORM_DEFAULT_THRESHOLD. If this threshold is exceeded, it's
+ * considered an irq storm and the irq state is set to @HPD_MARK_DISABLED.
+ *
+ * The HPD threshold can be controlled through i915_hpd_storm_ctl in debugfs,
+ * and should only be adjusted for automated hotplug testing.
  *
  * Return true if an irq storm was detected on @pin.
  */
@@ -123,13 +126,15 @@ static bool intel_hpd_irq_storm_detect(struct drm_i915_private *dev_priv,
 {
 	unsigned long start = dev_priv->hotplug.stats[pin].last_jiffies;
 	unsigned long end = start + msecs_to_jiffies(HPD_STORM_DETECT_PERIOD);
+	const int threshold = dev_priv->hotplug.hpd_storm_threshold;
 	bool storm = false;
 
 	if (!time_in_range(jiffies, start, end)) {
 		dev_priv->hotplug.stats[pin].last_jiffies = jiffies;
 		dev_priv->hotplug.stats[pin].count = 0;
 		DRM_DEBUG_KMS("Received HPD interrupt on PIN %d - cnt: 0\n", pin);
-	} else if (dev_priv->hotplug.stats[pin].count > HPD_STORM_THRESHOLD) {
+	} else if (dev_priv->hotplug.stats[pin].count > threshold &&
+		   threshold) {
 		dev_priv->hotplug.stats[pin].state = HPD_MARK_DISABLED;
 		DRM_DEBUG_KMS("HPD interrupt storm detected on PIN %d\n", pin);
 		storm = true;