i915/display/intel_hotplug.c

/*
 * Copyright © 2015 Intel Corporation
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice (including the next
 * paragraph) shall be included in all copies or substantial portions of the
 * Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 */

#include <linux/kernel.h>

#include "i915_drv.h"
#include "intel_display_types.h"
#include "intel_hotplug.h"

/**
 * DOC: Hotplug
 *
 * Simply put, hotplug occurs when a display is connected to or disconnected
 * from the system. However, there may be adapters and docking stations and
 * Display Port short pulses and MST devices involved, complicating matters.
 *
 * Hotplug in i915 is handled in many different levels of abstraction.
 *
 * The platform dependent interrupt handling code in i915_irq.c enables,
 * disables, and does preliminary handling of the interrupts. The interrupt
 * handlers gather the hotplug detect (HPD) information from relevant registers
 * into a platform independent mask of hotplug pins that have fired.
 *
 * The platform independent interrupt handler intel_hpd_irq_handler() in
 * intel_hotplug.c does hotplug irq storm detection and mitigation, and passes
 * further processing to appropriate bottom halves (Display Port specific and
 * regular hotplug).
 *
 * The Display Port work function i915_digport_work_func() calls into
 * intel_dp_hpd_pulse() via hooks, which handles DP short pulses and DP MST long
 * pulses, with failures and non-MST long pulses triggering regular hotplug
 * processing on the connector.
 *
 * The regular hotplug work function i915_hotplug_work_func() calls connector
 * detect hooks, and, if connector status changes, triggers sending of hotplug
 * uevent to userspace via drm_kms_helper_hotplug_event().
 *
 * Finally, the userspace is responsible for triggering a modeset upon receiving
 * the hotplug uevent, disabling or enabling the crtc as needed.
 *
 * The hotplug interrupt storm detection and mitigation code keeps track of the
 * number of interrupts per hotplug pin per a period of time, and if the number
 * of interrupts exceeds a certain threshold, the interrupt is disabled for a
 * while before being re-enabled. The intention is to mitigate issues raising
 * from broken hardware triggering massive amounts of interrupts and grinding
 * the system to a halt.
 *
 * Current implementation expects that hotplug interrupt storm will not be
 * seen when display port sink is connected, hence on platforms whose DP
 * callback is handled by i915_digport_work_func reenabling of hpd is not
 * performed (it was never expected to be disabled in the first place ;) )
 * this is specific to DP sinks handled by this routine and any other display
 * such as HDMI or DVI enabled on the same port will have proper logic since
 * it will use i915_hotplug_work_func where this logic is handled.
 */

/**
 * intel_hpd_pin_default - return default pin associated with certain port.
 * @dev_priv: private driver data pointer
 * @port: the hpd port to get associated pin
 *
 * It is only valid and used by digital port encoder.
 *
 * Return pin that is associatade with @port and HDP_NONE if no pin is
 * hard associated with that @port.
 */
enum hpd_pin intel_hpd_pin_default(struct drm_i915_private *dev_priv,
				   enum port port)
{
	enum phy phy = intel_port_to_phy(dev_priv, port);

	/*
	 * RKL + TGP PCH is a special case; we effectively choose the hpd_pin
	 * based on the DDI rather than the PHY (i.e., the last two outputs
	 * shold be HPD_PORT_{D,E} rather than {C,D}.  Note that this differs
	 * from the behavior of both TGL+TGP and RKL+CMP.
	 */
	if (IS_ROCKETLAKE(dev_priv) && HAS_PCH_TGP(dev_priv))
		return HPD_PORT_A + port - PORT_A;

	switch (phy) {
	case PHY_F:
		return IS_CNL_WITH_PORT_F(dev_priv) ? HPD_PORT_E : HPD_PORT_F;
	case PHY_A ... PHY_E:
	case PHY_G ... PHY_I:
		return HPD_PORT_A + phy - PHY_A;
	default:
		MISSING_CASE(phy);
		return HPD_NONE;
	}
}

#define HPD_STORM_DETECT_PERIOD		1000
#define HPD_STORM_REENABLE_DELAY	(2 * 60 * 1000)
#define HPD_RETRY_DELAY			1000

static enum hpd_pin
intel_connector_hpd_pin(struct intel_connector *connector)
{
	struct intel_encoder *encoder = intel_attached_encoder(connector);

	/*
	 * MST connectors get their encoder attached dynamically
	 * so need to make sure we have an encoder here. But since
	 * MST encoders have their hpd_pin set to HPD_NONE we don't
	 * have to special case them beyond that.
	 */
	return encoder ? encoder->hpd_pin : HPD_NONE;
}

/**
 * intel_hpd_irq_storm_detect - gather stats and detect HPD IRQ storm on a pin
 * @dev_priv: private driver data pointer
 * @pin: the pin to gather stats on
 * @long_hpd: whether the HPD IRQ was long or short
 *
 * Gather stats about HPD IRQs from the specified @pin, and detect IRQ
 * storms. Only the pin specific stats and state are changed, the caller is
 * responsible for further action.
 *
 * 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. Long IRQs count as +10 to this threshold, and
 * short IRQs count as +1. If this threshold is exceeded, it's considered an
 * IRQ storm and the IRQ state is set to @HPD_MARK_DISABLED.
 *
 * By default, most systems will only count long IRQs towards
 * &dev_priv->hotplug.hpd_storm_threshold. However, some older systems also
 * suffer from short IRQ storms and must also track these. Because short IRQ
 * storms are naturally caused by sideband interactions with DP MST devices,
 * short IRQ detection is only enabled for systems without DP MST support.
 * Systems which are new enough to support DP MST are far less likely to
 * suffer from IRQ storms at all, so this is fine.
 *
 * 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.
 */
static bool intel_hpd_irq_storm_detect(struct drm_i915_private *dev_priv,
				       enum hpd_pin pin, bool long_hpd)
{
	struct i915_hotplug *hpd = &dev_priv->hotplug;
	unsigned long start = hpd->stats[pin].last_jiffies;
	unsigned long end = start + msecs_to_jiffies(HPD_STORM_DETECT_PERIOD);
	const int increment = long_hpd ? 10 : 1;
	const int threshold = hpd->hpd_storm_threshold;
	bool storm = false;

	if (!threshold ||
	    (!long_hpd && !dev_priv->hotplug.hpd_short_storm_enabled))
		return false;

	if (!time_in_range(jiffies, start, end)) {
		hpd->stats[pin].last_jiffies = jiffies;
		hpd->stats[pin].count = 0;
	}

	hpd->stats[pin].count += increment;
	if (hpd->stats[pin].count > threshold) {
		hpd->stats[pin].state = HPD_MARK_DISABLED;
		drm_dbg_kms(&dev_priv->drm,
			    "HPD interrupt storm detected on PIN %d\n", pin);
		storm = true;
	} else {
		drm_dbg_kms(&dev_priv->drm,
			    "Received HPD interrupt on PIN %d - cnt: %d\n",
			      pin,
			      hpd->stats[pin].count);
	}

	return storm;
}

static void
intel_hpd_irq_storm_switch_to_polling(struct drm_i915_private *dev_priv)
{
	struct drm_device *dev = &dev_priv->drm;
	struct drm_connector_list_iter conn_iter;
	struct intel_connector *connector;
	bool hpd_disabled = false;

	lockdep_assert_held(&dev_priv->irq_lock);

	drm_connector_list_iter_begin(dev, &conn_iter);
	for_each_intel_connector_iter(connector, &conn_iter) {
		enum hpd_pin pin;

		if (connector->base.polled != DRM_CONNECTOR_POLL_HPD)
			continue;

		pin = intel_connector_hpd_pin(connector);
		if (pin == HPD_NONE ||
		    dev_priv->hotplug.stats[pin].state != HPD_MARK_DISABLED)
			continue;

		drm_info(&dev_priv->drm,
			 "HPD interrupt storm detected on connector %s: "
			 "switching from hotplug detection to polling\n",
			 connector->base.name);

		dev_priv->hotplug.stats[pin].state = HPD_DISABLED;
		connector->base.polled = DRM_CONNECTOR_POLL_CONNECT |
			DRM_CONNECTOR_POLL_DISCONNECT;
		hpd_disabled = true;
	}
	drm_connector_list_iter_end(&conn_iter);

	/* Enable polling and queue hotplug re-enabling. */
	if (hpd_disabled) {
		drm_kms_helper_poll_enable(dev);
		mod_delayed_work(system_wq, &dev_priv->hotplug.reenable_work,
				 msecs_to_jiffies(HPD_STORM_REENABLE_DELAY));
	}
}

static void intel_hpd_irq_storm_reenable_work(struct work_struct *work)
{
	struct drm_i915_private *dev_priv =
		container_of(work, typeof(*dev_priv),
			     hotplug.reenable_work.work);
	struct drm_device *dev = &dev_priv->drm;
	struct drm_connector_list_iter conn_iter;
	struct intel_connector *connector;
	intel_wakeref_t wakeref;
	enum hpd_pin pin;

	wakeref = intel_runtime_pm_get(&dev_priv->runtime_pm);

	spin_lock_irq(&dev_priv->irq_lock);

	drm_connector_list_iter_begin(dev, &conn_iter);
	for_each_intel_connector_iter(connector, &conn_iter) {
		pin = intel_connector_hpd_pin(connector);
		if (pin == HPD_NONE ||
		    dev_priv->hotplug.stats[pin].state != HPD_DISABLED)
			continue;

		if (connector->base.polled != connector->polled)
			drm_dbg(&dev_priv->drm,
				"Reenabling HPD on connector %s\n",
				connector->base.name);
		connector->base.polled = connector->polled;
	}
	drm_connector_list_iter_end(&conn_iter);

	for_each_hpd_pin(pin) {
		if (dev_priv->hotplug.stats[pin].state == HPD_DISABLED)
			dev_priv->hotplug.stats[pin].state = HPD_ENABLED;
	}

	if (dev_priv->display_irqs_enabled && dev_priv->display.hpd_irq_setup)
		dev_priv->display.hpd_irq_setup(dev_priv);

	spin_unlock_irq(&dev_priv->irq_lock);

	intel_runtime_pm_put(&dev_priv->runtime_pm, wakeref);
}

enum intel_hotplug_state
intel_encoder_hotplug(struct intel_encoder *encoder,
		      struct intel_connector *connector)
{
	struct drm_device *dev = connector->base.dev;
	enum drm_connector_status old_status;

	drm_WARN_ON(dev, !mutex_is_locked(&dev->mode_config.mutex));
	old_status = connector->base.status;

	connector->base.status =
		drm_helper_probe_detect(&connector->base, NULL, false);

	if (old_status == connector->base.status)
		return INTEL_HOTPLUG_UNCHANGED;

	drm_dbg_kms(&to_i915(dev)->drm,
		    "[CONNECTOR:%d:%s] status updated from %s to %s\n",
		    connector->base.base.id,
		    connector->base.name,
		    drm_get_connector_status_name(old_status),
		    drm_get_connector_status_name(connector->base.status));

	return INTEL_HOTPLUG_CHANGED;
}

static bool intel_encoder_has_hpd_pulse(struct intel_encoder *encoder)
{
	return intel_encoder_is_dig_port(encoder) &&
		enc_to_dig_port(encoder)->hpd_pulse != NULL;
}

static void i915_digport_work_func(struct work_struct *work)
{
	struct drm_i915_private *dev_priv =
		container_of(work, struct drm_i915_private, hotplug.dig_port_work);
	u32 long_port_mask, short_port_mask;
	struct intel_encoder *encoder;
	u32 old_bits = 0;

	spin_lock_irq(&dev_priv->irq_lock);
	long_port_mask = dev_priv->hotplug.long_port_mask;
	dev_priv->hotplug.long_port_mask = 0;
	short_port_mask = dev_priv->hotplug.short_port_mask;
	dev_priv->hotplug.short_port_mask = 0;
	spin_unlock_irq(&dev_priv->irq_lock);

	for_each_intel_encoder(&dev_priv->drm, encoder) {
		struct intel_digital_port *dig_port;
		enum port port = encoder->port;
		bool long_hpd, short_hpd;
		enum irqreturn ret;

		if (!intel_encoder_has_hpd_pulse(encoder))
			continue;

		long_hpd = long_port_mask & BIT(port);
		short_hpd = short_port_mask & BIT(port);

		if (!long_hpd && !short_hpd)
			continue;

		dig_port = enc_to_dig_port(encoder);

		ret = dig_port->hpd_pulse(dig_port, long_hpd);
		if (ret == IRQ_NONE) {
			/* fall back to old school hpd */
			old_bits |= BIT(encoder->hpd_pin);
		}
	}

	if (old_bits) {
		spin_lock_irq(&dev_priv->irq_lock);
		dev_priv->hotplug.event_bits |= old_bits;
		spin_unlock_irq(&dev_priv->irq_lock);
		queue_delayed_work(system_wq, &dev_priv->hotplug.hotplug_work, 0);
	}
}

/*
 * Handle hotplug events outside the interrupt handler proper.
 */
static void i915_hotplug_work_func(struct work_struct *work)
{
	struct drm_i915_private *dev_priv =
		container_of(work, struct drm_i915_private,
			     hotplug.hotplug_work.work);
	struct drm_device *dev = &dev_priv->drm;
	struct drm_connector_list_iter conn_iter;
	struct intel_connector *connector;
	u32 changed = 0, retry = 0;
	u32 hpd_event_bits;
	u32 hpd_retry_bits;

	mutex_lock(&dev->mode_config.mutex);
	drm_dbg_kms(&dev_priv->drm, "running encoder hotplug functions\n");

	spin_lock_irq(&dev_priv->irq_lock);

	hpd_event_bits = dev_priv->hotplug.event_bits;
	dev_priv->hotplug.event_bits = 0;
	hpd_retry_bits = dev_priv->hotplug.retry_bits;
	dev_priv->hotplug.retry_bits = 0;

	/* Enable polling for connectors which had HPD IRQ storms */
	intel_hpd_irq_storm_switch_to_polling(dev_priv);

	spin_unlock_irq(&dev_priv->irq_lock);

	drm_connector_list_iter_begin(dev, &conn_iter);
	for_each_intel_connector_iter(connector, &conn_iter) {
		enum hpd_pin pin;
		u32 hpd_bit;

		pin = intel_connector_hpd_pin(connector);
		if (pin == HPD_NONE)
			continue;

		hpd_bit = BIT(pin);
		if ((hpd_event_bits | hpd_retry_bits) & hpd_bit) {
			struct intel_encoder *encoder =
				intel_attached_encoder(connector);

			if (hpd_event_bits & hpd_bit)
				connector->hotplug_retries = 0;
			else
				connector->hotplug_retries++;

			drm_dbg_kms(&dev_priv->drm,
				    "Connector %s (pin %i) received hotplug event. (retry %d)\n",
				    connector->base.name, pin,
				    connector->hotplug_retries);

			switch (encoder->hotplug(encoder, connector)) {
			case INTEL_HOTPLUG_UNCHANGED:
				break;
			case INTEL_HOTPLUG_CHANGED:
				changed |= hpd_bit;
				break;
			case INTEL_HOTPLUG_RETRY:
				retry |= hpd_bit;
				break;
			}
		}
	}
	drm_connector_list_iter_end(&conn_iter);
	mutex_unlock(&dev->mode_config.mutex);

	if (changed)
		drm_kms_helper_hotplug_event(dev);

	/* Remove shared HPD pins that have changed */
	retry &= ~changed;
	if (retry) {
		spin_lock_irq(&dev_priv->irq_lock);
		dev_priv->hotplug.retry_bits |= retry;
		spin_unlock_irq(&dev_priv->irq_lock);

		mod_delayed_work(system_wq, &dev_priv->hotplug.hotplug_work,
				 msecs_to_jiffies(HPD_RETRY_DELAY));
	}
}


/**
 * intel_hpd_irq_handler - main hotplug irq handler
 * @dev_priv: drm_i915_private
 * @pin_mask: a mask of hpd pins that have triggered the irq
 * @long_mask: a mask of hpd pins that may be long hpd pulses
 *
 * This is the main hotplug irq handler for all platforms. The platform specific
 * irq handlers call the platform specific hotplug irq handlers, which read and
 * decode the appropriate registers into bitmasks about hpd pins that have
 * triggered (@pin_mask), and which of those pins may be long pulses
 * (@long_mask). The @long_mask is ignored if the port corresponding to the pin
 * is not a digital port.
 *
 * Here, we do hotplug irq storm detection and mitigation, and pass further
 * processing to appropriate bottom halves.
 */
void intel_hpd_irq_handler(struct drm_i915_private *dev_priv,
			   u32 pin_mask, u32 long_mask)
{
	struct intel_encoder *encoder;
	bool storm_detected = false;
	bool queue_dig = false, queue_hp = false;
	u32 long_hpd_pulse_mask = 0;
	u32 short_hpd_pulse_mask = 0;
	enum hpd_pin pin;

	if (!pin_mask)
		return;

	spin_lock(&dev_priv->irq_lock);

	/*
	 * Determine whether ->hpd_pulse() exists for each pin, and
	 * whether we have a short or a long pulse. This is needed
	 * as each pin may have up to two encoders (HDMI and DP) and
	 * only the one of them (DP) will have ->hpd_pulse().
	 */
	for_each_intel_encoder(&dev_priv->drm, encoder) {
		bool has_hpd_pulse = intel_encoder_has_hpd_pulse(encoder);
		enum port port = encoder->port;
		bool long_hpd;

		pin = encoder->hpd_pin;
		if (!(BIT(pin) & pin_mask))
			continue;

		if (!has_hpd_pulse)
			continue;

		long_hpd = long_mask & BIT(pin);

		drm_dbg(&dev_priv->drm,
			"digital hpd on [ENCODER:%d:%s] - %s\n",
			encoder->base.base.id, encoder->base.name,
			long_hpd ? "long" : "short");
		queue_dig = true;

		if (long_hpd) {
			long_hpd_pulse_mask |= BIT(pin);
			dev_priv->hotplug.long_port_mask |= BIT(port);
		} else {
			short_hpd_pulse_mask |= BIT(pin);
			dev_priv->hotplug.short_port_mask |= BIT(port);
		}
	}

	/* Now process each pin just once */
	for_each_hpd_pin(pin) {
		bool long_hpd;

		if (!(BIT(pin) & pin_mask))
			continue;

		if (dev_priv->hotplug.stats[pin].state == HPD_DISABLED) {
			/*
			 * On GMCH platforms the interrupt mask bits only
			 * prevent irq generation, not the setting of the
			 * hotplug bits itself. So only WARN about unexpected
			 * interrupts on saner platforms.
			 */
			drm_WARN_ONCE(&dev_priv->drm, !HAS_GMCH(dev_priv),
				      "Received HPD interrupt on pin %d although disabled\n",
				      pin);
			continue;
		}

		if (dev_priv->hotplug.stats[pin].state != HPD_ENABLED)
			continue;

		/*
		 * Delegate to ->hpd_pulse() if one of the encoders for this
		 * pin has it, otherwise let the hotplug_work deal with this
		 * pin directly.
		 */
		if (((short_hpd_pulse_mask | long_hpd_pulse_mask) & BIT(pin))) {
			long_hpd = long_hpd_pulse_mask & BIT(pin);
		} else {
			dev_priv->hotplug.event_bits |= BIT(pin);
			long_hpd = true;
			queue_hp = true;
		}

		if (intel_hpd_irq_storm_detect(dev_priv, pin, long_hpd)) {
			dev_priv->hotplug.event_bits &= ~BIT(pin);
			storm_detected = true;
			queue_hp = true;
		}
	}

	/*
	 * Disable any IRQs that storms were detected on. Polling enablement
	 * happens later in our hotplug work.
	 */
	if (storm_detected && dev_priv->display_irqs_enabled)
		dev_priv->display.hpd_irq_setup(dev_priv);
	spin_unlock(&dev_priv->irq_lock);

	/*
	 * Our hotplug handler can grab modeset locks (by calling down into the
	 * fb helpers). Hence it must not be run on our own dev-priv->wq work
	 * queue for otherwise the flush_work in the pageflip code will
	 * deadlock.
	 */
	if (queue_dig)
		queue_work(dev_priv->hotplug.dp_wq, &dev_priv->hotplug.dig_port_work);
	if (queue_hp)
		queue_delayed_work(system_wq, &dev_priv->hotplug.hotplug_work, 0);
}

/**
 * intel_hpd_init - initializes and enables hpd support
 * @dev_priv: i915 device instance
 *
 * This function enables the hotplug support. It requires that interrupts have
 * already been enabled with intel_irq_init_hw(). From this point on hotplug and
 * poll request can run concurrently to other code, so locking rules must be
 * obeyed.
 *
 * This is a separate step from interrupt enabling to simplify the locking rules
 * in the driver load and resume code.
 *
 * Also see: intel_hpd_poll_init(), which enables connector polling
 */
void intel_hpd_init(struct drm_i915_private *dev_priv)
{
	int i;

	for_each_hpd_pin(i) {
		dev_priv->hotplug.stats[i].count = 0;
		dev_priv->hotplug.stats[i].state = HPD_ENABLED;
	}

	WRITE_ONCE(dev_priv->hotplug.poll_enabled, false);
	schedule_work(&dev_priv->hotplug.poll_init_work);

	/*
	 * Interrupt setup is already guaranteed to be single-threaded, this is
	 * just to make the assert_spin_locked checks happy.
	 */
	if (dev_priv->display_irqs_enabled && dev_priv->display.hpd_irq_setup) {
		spin_lock_irq(&dev_priv->irq_lock);
		if (dev_priv->display_irqs_enabled)
			dev_priv->display.hpd_irq_setup(dev_priv);
		spin_unlock_irq(&dev_priv->irq_lock);
	}
}

static void i915_hpd_poll_init_work(struct work_struct *work)
{
	struct drm_i915_private *dev_priv =
		container_of(work, struct drm_i915_private,
			     hotplug.poll_init_work);
	struct drm_device *dev = &dev_priv->drm;
	struct drm_connector_list_iter conn_iter;
	struct intel_connector *connector;
	bool enabled;

	mutex_lock(&dev->mode_config.mutex);

	enabled = READ_ONCE(dev_priv->hotplug.poll_enabled);

	drm_connector_list_iter_begin(dev, &conn_iter);
	for_each_intel_connector_iter(connector, &conn_iter) {
		enum hpd_pin pin;

		pin = intel_connector_hpd_pin(connector);
		if (pin == HPD_NONE)
			continue;

		connector->base.polled = connector->polled;

		if (enabled && connector->base.polled == DRM_CONNECTOR_POLL_HPD)
			connector->base.polled = DRM_CONNECTOR_POLL_CONNECT |
				DRM_CONNECTOR_POLL_DISCONNECT;
	}
	drm_connector_list_iter_end(&conn_iter);

	if (enabled)
		drm_kms_helper_poll_enable(dev);

	mutex_unlock(&dev->mode_config.mutex);

	/*
	 * We might have missed any hotplugs that happened while we were
	 * in the middle of disabling polling
	 */
	if (!enabled)
		drm_helper_hpd_irq_event(dev);
}

/**
 * intel_hpd_poll_init - enables/disables polling for connectors with hpd
 * @dev_priv: i915 device instance
 *
 * This function enables polling for all connectors, regardless of whether or
 * not they support hotplug detection. Under certain conditions HPD may not be
 * functional. On most Intel GPUs, this happens when we enter runtime suspend.
 * On Valleyview and Cherryview systems, this also happens when we shut off all
 * of the powerwells.
 *
 * Since this function can get called in contexts where we're already holding
 * dev->mode_config.mutex, we do the actual hotplug enabling in a seperate
 * worker.
 *
 * Also see: intel_hpd_init(), which restores hpd handling.
 */
void intel_hpd_poll_init(struct drm_i915_private *dev_priv)
{
	WRITE_ONCE(dev_priv->hotplug.poll_enabled, true);

	/*
	 * We might already be holding dev->mode_config.mutex, so do this in a
	 * seperate worker
	 * As well, there's no issue if we race here since we always reschedule
	 * this worker anyway
	 */
	schedule_work(&dev_priv->hotplug.poll_init_work);
}

void intel_hpd_init_work(struct drm_i915_private *dev_priv)
{
	INIT_DELAYED_WORK(&dev_priv->hotplug.hotplug_work,
			  i915_hotplug_work_func);
	INIT_WORK(&dev_priv->hotplug.dig_port_work, i915_digport_work_func);
	INIT_WORK(&dev_priv->hotplug.poll_init_work, i915_hpd_poll_init_work);
	INIT_DELAYED_WORK(&dev_priv->hotplug.reenable_work,
			  intel_hpd_irq_storm_reenable_work);
}

void intel_hpd_cancel_work(struct drm_i915_private *dev_priv)
{
	spin_lock_irq(&dev_priv->irq_lock);

	dev_priv->hotplug.long_port_mask = 0;
	dev_priv->hotplug.short_port_mask = 0;
	dev_priv->hotplug.event_bits = 0;
	dev_priv->hotplug.retry_bits = 0;

	spin_unlock_irq(&dev_priv->irq_lock);

	cancel_work_sync(&dev_priv->hotplug.dig_port_work);
	cancel_delayed_work_sync(&dev_priv->hotplug.hotplug_work);
	cancel_work_sync(&dev_priv->hotplug.poll_init_work);
	cancel_delayed_work_sync(&dev_priv->hotplug.reenable_work);
}

bool intel_hpd_disable(struct drm_i915_private *dev_priv, enum hpd_pin pin)
{
	bool ret = false;

	if (pin == HPD_NONE)
		return false;

	spin_lock_irq(&dev_priv->irq_lock);
	if (dev_priv->hotplug.stats[pin].state == HPD_ENABLED) {
		dev_priv->hotplug.stats[pin].state = HPD_DISABLED;
		ret = true;
	}
	spin_unlock_irq(&dev_priv->irq_lock);

	return ret;
}

void intel_hpd_enable(struct drm_i915_private *dev_priv, enum hpd_pin pin)
{
	if (pin == HPD_NONE)
		return;

	spin_lock_irq(&dev_priv->irq_lock);
	dev_priv->hotplug.stats[pin].state = HPD_ENABLED;
	spin_unlock_irq(&dev_priv->irq_lock);
}