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 /*
  * 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 "i915_irq.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.
  */
 enum hpd_pin intel_hpd_pin_default(struct drm_i915_private *dev_priv,
                    enum port port)
 {
     return HPD_PORT_A + port - PORT_A;
 }
 
 #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;
     }
 
     intel_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;
     u64 old_epoch_counter;
     bool ret = false;
 
     drm_WARN_ON(dev, !mutex_is_locked(&dev->mode_config.mutex));
     old_status = connector->base.status;
     old_epoch_counter = connector->base.epoch_counter;
 
     connector->base.status =
         drm_helper_probe_detect(&connector->base, NULL, false);
 
     if (old_epoch_counter != connector->base.epoch_counter)
         ret = true;
 
     if (ret) {
         drm_dbg_kms(dev, "[CONNECTOR:%d:%s] status updated from %s to %s (epoch counter %llu->%llu)\n",
                 connector->base.base.id,
                 connector->base.name,
                 drm_get_connector_status_name(old_status),
                 drm_get_connector_status_name(connector->base.status),
                 old_epoch_counter,
                 connector->base.epoch_counter);
         return INTEL_HOTPLUG_CHANGED;
     }
     return INTEL_HOTPLUG_UNCHANGED;
 }
 
 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);
     }
 }
 
 /**
  * intel_hpd_trigger_irq - trigger an hpd irq event for a port
  * @dig_port: digital port
  *
  * Trigger an HPD interrupt event for the given port, emulating a short pulse
  * generated by the sink, and schedule the dig port work to handle it.
  */
 void intel_hpd_trigger_irq(struct intel_digital_port *dig_port)
 {
     struct drm_i915_private *i915 = to_i915(dig_port->base.base.dev);
 
     spin_lock_irq(&i915->irq_lock);
     i915->hotplug.short_port_mask |= BIT(dig_port->base.port);
     spin_unlock_irq(&i915->irq_lock);
 
     queue_work(i915->hotplug.dp_wq, &i915->hotplug.dig_port_work);
 }
 
 /*
  * 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) {
         enum port port = encoder->port;
         bool long_hpd;
 
         pin = encoder->hpd_pin;
         if (!(BIT(pin) & pin_mask))
             continue;
 
         if (!intel_encoder_has_hpd_pulse(encoder))
             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)
         intel_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_enable() and intel_hpd_poll_disable().
  */
 void intel_hpd_init(struct drm_i915_private *dev_priv)
 {
     int i;
 
     if (!HAS_DISPLAY(dev_priv))
         return;
 
     for_each_hpd_pin(i) {
         dev_priv->hotplug.stats[i].count = 0;
         dev_priv->hotplug.stats[i].state = HPD_ENABLED;
     }
 
     /*
      * Interrupt setup is already guaranteed to be single-threaded, this is
      * just to make the assert_spin_locked checks happy.
      */
     spin_lock_irq(&dev_priv->irq_lock);
     intel_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_enable - enable polling for connectors with hpd
  * @dev_priv: i915 device instance
  *
  * This function enables polling for all connectors which support HPD.
  * 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() and intel_hpd_poll_disable().
  */
 void intel_hpd_poll_enable(struct drm_i915_private *dev_priv)
 {
     if (!HAS_DISPLAY(dev_priv) ||
         !INTEL_DISPLAY_ENABLED(dev_priv))
         return;
 
     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);
 }
 
 /**
  * intel_hpd_poll_disable - disable polling for connectors with hpd
  * @dev_priv: i915 device instance
  *
  * This function disables polling for all connectors which support HPD.
  * 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 used during driver init to initialize connector->polled
  * appropriately for all connectors.
  *
  * Also see: intel_hpd_init() and intel_hpd_poll_enable().
  */
 void intel_hpd_poll_disable(struct drm_i915_private *dev_priv)
 {
     if (!HAS_DISPLAY(dev_priv))
         return;
 
     WRITE_ONCE(dev_priv->hotplug.poll_enabled, false);
     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)
 {
     if (!HAS_DISPLAY(dev_priv))
         return;
 
     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);
 }

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