[PATCH v4 0/5] drm/i915: HPD IRQ storm detection fixes

[PATCH v4 0/5] drm/i915: HPD IRQ storm detection fixes

[Lyude Paul]

This series contains a fix for a problem which is very difficult to
reproduce under normal circumstances without specialized testing
hardware, along with a fix that seems to be required for some especially
rebellious GM45 laptops.

Lyude Paul (5):
  drm/i915: Fix possible race in intel_dp_add_mst_connector()
  drm/i915: Fix NULL deref when re-enabling HPD IRQs on systems with MST
  drm/i915: Fix threshold check in intel_hpd_irq_storm_detect()
  drm/i915: Clarify flow for disabling IRQs on storms
  drm/i915: Add short HPD IRQ storm detection for non-MST systems

 drivers/gpu/drm/i915/i915_debugfs.c  | 74 +++++++++++++++++++++++++
 drivers/gpu/drm/i915/i915_drv.h      |  5 +-
 drivers/gpu/drm/i915/i915_irq.c      |  7 +++
 drivers/gpu/drm/i915/intel_dp_mst.c  |  8 +--
 drivers/gpu/drm/i915/intel_hotplug.c | 83 +++++++++++++++++-----------
 5 files changed, 140 insertions(+), 37 deletions(-)

-- 
2.19.1

[PATCH v4 1/5] drm/i915: Fix possible race in intel_dp_add_mst_connector()

[Lyude Paul]

This hasn't caused any issues yet that I'm aware of, but as Ville
Syrjälä pointed out - we need to make sure that
intel_connector->mst_port is set before initializing MST connectors,
since in theory we could potentially check intel_connector->mst_port in
i915_hpd_poll_init_work() after registering the connector but before
having written it's value.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
---
 drivers/gpu/drm/i915/intel_dp_mst.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_dp_mst.c b/drivers/gpu/drm/i915/intel_dp_mst.c
index 8b71d64ebd9d..8cb4093f8bcc 100644
--- a/drivers/gpu/drm/i915/intel_dp_mst.c
+++ b/drivers/gpu/drm/i915/intel_dp_mst.c
@@ -441,6 +441,10 @@ static struct drm_connector *intel_dp_add_mst_connector(struct drm_dp_mst_topolo
 	if (!intel_connector)
 		return NULL;
 
+	intel_connector->get_hw_state = intel_dp_mst_get_hw_state;
+	intel_connector->mst_port = intel_dp;
+	intel_connector->port = port;
+
 	connector = &intel_connector->base;
 	ret = drm_connector_init(dev, connector, &intel_dp_mst_connector_funcs,
 				 DRM_MODE_CONNECTOR_DisplayPort);
@@ -451,10 +455,6 @@ static struct drm_connector *intel_dp_add_mst_connector(struct drm_dp_mst_topolo
 
 	drm_connector_helper_add(connector, &intel_dp_mst_connector_helper_funcs);
 
-	intel_connector->get_hw_state = intel_dp_mst_get_hw_state;
-	intel_connector->mst_port = intel_dp;
-	intel_connector->port = port;
-
 	for_each_pipe(dev_priv, pipe) {
 		struct drm_encoder *enc =
 			&intel_dp->mst_encoders[pipe]->base.base;
-- 
2.19.1

[PATCH v4 2/5] drm/i915: Fix NULL deref when re-enabling HPD IRQs on systems with MST

[Lyude Paul]

Turns out that if you trigger an HPD storm on a system that has an MST
topology connected to it, you'll end up causing the kernel to eventually
hit a NULL deref:

[  332.339041] BUG: unable to handle kernel NULL pointer dereference at 00000000000000ec
[  332.340906] PGD 0 P4D 0
[  332.342750] Oops: 0000 [#1] SMP PTI
[  332.344579] CPU: 2 PID: 25 Comm: kworker/2:0 Kdump: loaded Tainted: G           O      4.18.0-rc3short-hpd-storm+ #2
[  332.346453] Hardware name: LENOVO 20BWS1KY00/20BWS1KY00, BIOS JBET71WW (1.35 ) 09/14/2018
[  332.348361] Workqueue: events intel_hpd_irq_storm_reenable_work [i915]
[  332.350301] RIP: 0010:intel_hpd_irq_storm_reenable_work.cold.3+0x2f/0x86 [i915]
[  332.352213] Code: 00 00 ba e8 00 00 00 48 c7 c6 c0 aa 5f a0 48 c7 c7 d0 73 62 a0 4c 89 c1 4c 89 04 24 e8 7f f5 af e0 4c 8b 04 24 44 89 f8 29 e8 <41> 39 80 ec 00 00 00 0f 85 43 13 fc ff 41 0f b6 86 b8 04 00 00 41
[  332.354286] RSP: 0018:ffffc90000147e48 EFLAGS: 00010006
[  332.356344] RAX: 0000000000000005 RBX: ffff8802c226c9d4 RCX: 0000000000000006
[  332.358404] RDX: 0000000000000000 RSI: 0000000000000082 RDI: ffff88032dc95570
[  332.360466] RBP: 0000000000000005 R08: 0000000000000000 R09: ffff88031b3dc840
[  332.362528] R10: 0000000000000000 R11: 000000031a069602 R12: ffff8802c226ca20
[  332.364575] R13: ffff8802c2268000 R14: ffff880310661000 R15: 000000000000000a
[  332.366615] FS:  0000000000000000(0000) GS:ffff88032dc80000(0000) knlGS:0000000000000000
[  332.368658] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  332.370690] CR2: 00000000000000ec CR3: 000000000200a003 CR4: 00000000003606e0
[  332.372724] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  332.374773] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  332.376798] Call Trace:
[  332.378809]  process_one_work+0x1a1/0x350
[  332.380806]  worker_thread+0x30/0x380
[  332.382777]  ? wq_update_unbound_numa+0x10/0x10
[  332.384772]  kthread+0x112/0x130
[  332.386740]  ? kthread_create_worker_on_cpu+0x70/0x70
[  332.388706]  ret_from_fork+0x35/0x40
[  332.390651] Modules linked in: i915(O) vfat fat joydev btusb btrtl btbcm btintel bluetooth ecdh_generic iTCO_wdt wmi_bmof i2c_algo_bit drm_kms_helper intel_rapl syscopyarea sysfillrect x86_pkg_temp_thermal sysimgblt coretemp fb_sys_fops crc32_pclmul drm psmouse pcspkr mei_me mei i2c_i801 lpc_ich mfd_core i2c_core tpm_tis tpm_tis_core thinkpad_acpi wmi tpm rfkill video crc32c_intel serio_raw ehci_pci xhci_pci ehci_hcd xhci_hcd [last unloaded: i915]
[  332.394963] CR2: 00000000000000ec

This appears to be due to the fact that with an MST topology, not all
intel_connector structs will have ->encoder set. So, fix this by
skipping connectors without encoders in
intel_hpd_irq_storm_reenable_work().

For those wondering, this bug was found on accident while simulating HPD
storms using a Chamelium connected to a ThinkPad T450s (Broadwell).

Changes since v1:
- Check intel_connector->mst_port instead of intel_connector->encoder

Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
---
 drivers/gpu/drm/i915/intel_hotplug.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_hotplug.c b/drivers/gpu/drm/i915/intel_hotplug.c
index 648a13c6043c..8326900a311e 100644
--- a/drivers/gpu/drm/i915/intel_hotplug.c
+++ b/drivers/gpu/drm/i915/intel_hotplug.c
@@ -228,7 +228,9 @@ static void intel_hpd_irq_storm_reenable_work(struct work_struct *work)
 		drm_for_each_connector_iter(connector, &conn_iter) {
 			struct intel_connector *intel_connector = to_intel_connector(connector);
 
-			if (intel_connector->encoder->hpd_pin == pin) {
+			/* Don't check MST ports, they don't have pins */
+			if (!intel_connector->mst_port &&
+			    intel_connector->encoder->hpd_pin == pin) {
 				if (connector->polled != intel_connector->polled)
 					DRM_DEBUG_DRIVER("Reenabling HPD on connector %s\n",
 							 connector->name);
-- 
2.19.1

[PATCH v4 3/5] drm/i915: Fix threshold check in intel_hpd_irq_storm_detect()

[Lyude Paul]

Currently in intel_hpd_irq_storm_detect() when we detect that the last
recorded hotplug wasn't within the period defined by
HPD_STORM_DETECT_DELAY, we make the mistake of resetting the HPD count
to 0 without incrementing it. This results in us only enabling storm
detection when we go +2 above the threshold, e.g. an HPD threshold of 5
would not trigger a storm until we reach a total of 7 hotplugs.

So: rework the code a bit so we reset the HPD count when
HPD_STORM_DETECT_DELAY has passed, then increment the count afterwards.
Also, clean things up a bit to make it easier to undertand.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
---
 drivers/gpu/drm/i915/intel_hotplug.c | 23 +++++++++++++----------
 1 file changed, 13 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_hotplug.c b/drivers/gpu/drm/i915/intel_hotplug.c
index 8326900a311e..c11d73de16f2 100644
--- a/drivers/gpu/drm/i915/intel_hotplug.c
+++ b/drivers/gpu/drm/i915/intel_hotplug.c
@@ -135,24 +135,27 @@ enum hpd_pin intel_hpd_pin_default(struct drm_i915_private *dev_priv,
 static bool intel_hpd_irq_storm_detect(struct drm_i915_private *dev_priv,
 				       enum hpd_pin pin)
 {
-	unsigned long start = dev_priv->hotplug.stats[pin].last_jiffies;
+	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 threshold = dev_priv->hotplug.hpd_storm_threshold;
+	const int threshold = hpd->hpd_storm_threshold;
 	bool storm = false;
 
+	if (!threshold)
+		return 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 > threshold &&
-		   threshold) {
-		dev_priv->hotplug.stats[pin].state = HPD_MARK_DISABLED;
+		hpd->stats[pin].last_jiffies = jiffies;
+		hpd->stats[pin].count = 0;
+	}
+
+	if (++hpd->stats[pin].count > threshold) {
+		hpd->stats[pin].state = HPD_MARK_DISABLED;
 		DRM_DEBUG_KMS("HPD interrupt storm detected on PIN %d\n", pin);
 		storm = true;
 	} else {
-		dev_priv->hotplug.stats[pin].count++;
 		DRM_DEBUG_KMS("Received HPD interrupt on PIN %d - cnt: %d\n", pin,
-			      dev_priv->hotplug.stats[pin].count);
+			      hpd->stats[pin].count);
 	}
 
 	return storm;
-- 
2.19.1

Re: [PATCH v4 3/5] drm/i915: Fix threshold check in intel_hpd_irq_storm_detect()

[Ville Syrjälä]

On Mon, Nov 05, 2018 at 05:20:09PM -0500, Lyude Paul wrote:
> Currently in intel_hpd_irq_storm_detect() when we detect that the last
> recorded hotplug wasn't within the period defined by
> HPD_STORM_DETECT_DELAY, we make the mistake of resetting the HPD count
> to 0 without incrementing it. This results in us only enabling storm
> detection when we go +2 above the threshold, e.g. an HPD threshold of 5
> would not trigger a storm until we reach a total of 7 hotplugs.
> 
> So: rework the code a bit so we reset the HPD count when
> HPD_STORM_DETECT_DELAY has passed, then increment the count afterwards.
> Also, clean things up a bit to make it easier to undertand.
> 
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Signed-off-by: Lyude Paul <lyude@redhat.com>
> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>

Looks good to me
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

> ---
>  drivers/gpu/drm/i915/intel_hotplug.c | 23 +++++++++++++----------
>  1 file changed, 13 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_hotplug.c b/drivers/gpu/drm/i915/intel_hotplug.c
> index 8326900a311e..c11d73de16f2 100644
> --- a/drivers/gpu/drm/i915/intel_hotplug.c
> +++ b/drivers/gpu/drm/i915/intel_hotplug.c
> @@ -135,24 +135,27 @@ enum hpd_pin intel_hpd_pin_default(struct drm_i915_private *dev_priv,
>  static bool intel_hpd_irq_storm_detect(struct drm_i915_private *dev_priv,
>  				       enum hpd_pin pin)
>  {
> -	unsigned long start = dev_priv->hotplug.stats[pin].last_jiffies;
> +	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 threshold = dev_priv->hotplug.hpd_storm_threshold;
> +	const int threshold = hpd->hpd_storm_threshold;
>  	bool storm = false;
>  
> +	if (!threshold)
> +		return 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 > threshold &&
> -		   threshold) {
> -		dev_priv->hotplug.stats[pin].state = HPD_MARK_DISABLED;
> +		hpd->stats[pin].last_jiffies = jiffies;
> +		hpd->stats[pin].count = 0;
> +	}
> +
> +	if (++hpd->stats[pin].count > threshold) {
> +		hpd->stats[pin].state = HPD_MARK_DISABLED;
>  		DRM_DEBUG_KMS("HPD interrupt storm detected on PIN %d\n", pin);
>  		storm = true;
>  	} else {
> -		dev_priv->hotplug.stats[pin].count++;
>  		DRM_DEBUG_KMS("Received HPD interrupt on PIN %d - cnt: %d\n", pin,
> -			      dev_priv->hotplug.stats[pin].count);
> +			      hpd->stats[pin].count);
>  	}
>  
>  	return storm;
> -- 
> 2.19.1

-- 
Ville Syrjälä
Intel

[PATCH v4 4/5] drm/i915: Clarify flow for disabling IRQs on storms

[Lyude Paul]

This is rather confusing to look at as-is:
dev_priv->display.hpd_irq_setup(dev_priv); in intel_hpd_irq_handler()
handles disabling the actual HPD IRQ, while
intel_hpd_irq_storm_disable() handles moving the HPD pin state over from
MARK_DISABLED to DISABLED along with enabling polling for it.

Changes since v3:
- Rename i915_hpd_irq_storm_disable() to
  i915_hpd_irq_storm_switch_to_polling() - Rodrigo Vivi

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
---
 drivers/gpu/drm/i915/intel_hotplug.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_hotplug.c b/drivers/gpu/drm/i915/intel_hotplug.c
index c11d73de16f2..d642c0795452 100644
--- a/drivers/gpu/drm/i915/intel_hotplug.c
+++ b/drivers/gpu/drm/i915/intel_hotplug.c
@@ -161,7 +161,8 @@ static bool intel_hpd_irq_storm_detect(struct drm_i915_private *dev_priv,
 	return storm;
 }
 
-static void intel_hpd_irq_storm_disable(struct drm_i915_private *dev_priv)
+static void
+intel_hpd_irq_storm_switch_to_polling(struct drm_i915_private *dev_priv)
 {
 	struct drm_device *dev = &dev_priv->drm;
 	struct intel_connector *intel_connector;
@@ -351,8 +352,8 @@ static void i915_hotplug_work_func(struct work_struct *work)
 	hpd_event_bits = dev_priv->hotplug.event_bits;
 	dev_priv->hotplug.event_bits = 0;
 
-	/* Disable hotplug on connectors that hit an irq storm. */
-	intel_hpd_irq_storm_disable(dev_priv);
+	/* 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);
 
@@ -458,6 +459,10 @@ void intel_hpd_irq_handler(struct drm_i915_private *dev_priv,
 		}
 	}
 
+	/*
+	 * 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);
-- 
2.19.1

Re: [PATCH v4 4/5] drm/i915: Clarify flow for disabling IRQs on storms

[Ville Syrjälä]

On Mon, Nov 05, 2018 at 05:20:10PM -0500, Lyude Paul wrote:
> This is rather confusing to look at as-is:
> dev_priv->display.hpd_irq_setup(dev_priv); in intel_hpd_irq_handler()
> handles disabling the actual HPD IRQ, while
> intel_hpd_irq_storm_disable() handles moving the HPD pin state over from
> MARK_DISABLED to DISABLED along with enabling polling for it.
> 
> Changes since v3:
> - Rename i915_hpd_irq_storm_disable() to
>   i915_hpd_irq_storm_switch_to_polling() - Rodrigo Vivi
> 
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Signed-off-by: Lyude Paul <lyude@redhat.com>
> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

> ---
>  drivers/gpu/drm/i915/intel_hotplug.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_hotplug.c b/drivers/gpu/drm/i915/intel_hotplug.c
> index c11d73de16f2..d642c0795452 100644
> --- a/drivers/gpu/drm/i915/intel_hotplug.c
> +++ b/drivers/gpu/drm/i915/intel_hotplug.c
> @@ -161,7 +161,8 @@ static bool intel_hpd_irq_storm_detect(struct drm_i915_private *dev_priv,
>  	return storm;
>  }
>  
> -static void intel_hpd_irq_storm_disable(struct drm_i915_private *dev_priv)
> +static void
> +intel_hpd_irq_storm_switch_to_polling(struct drm_i915_private *dev_priv)
>  {
>  	struct drm_device *dev = &dev_priv->drm;
>  	struct intel_connector *intel_connector;
> @@ -351,8 +352,8 @@ static void i915_hotplug_work_func(struct work_struct *work)
>  	hpd_event_bits = dev_priv->hotplug.event_bits;
>  	dev_priv->hotplug.event_bits = 0;
>  
> -	/* Disable hotplug on connectors that hit an irq storm. */
> -	intel_hpd_irq_storm_disable(dev_priv);
> +	/* 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);
>  
> @@ -458,6 +459,10 @@ void intel_hpd_irq_handler(struct drm_i915_private *dev_priv,
>  		}
>  	}
>  
> +	/*
> +	 * 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);
> -- 
> 2.19.1

-- 
Ville Syrjälä
Intel

[PATCH v4 5/5] drm/i915: Add short HPD IRQ storm detection for non-MST systems

[Lyude Paul]

Unfortunately, it seems that the HPD IRQ storm problem from the early
days of Intel GPUs was never entirely solved, only mostly. Within the
last couple of days, I got a bug report from one of our customers who
had been having issues with their machine suddenly booting up very
slowly after having updated. The amount of time it took to boot went
from around 30 seconds, to over 6 minutes consistently.

After some investigation, I discovered that i915 was reporting massive
amounts of short HPD IRQ spam on this system from the DisplayPort port,
despite there not being anything actually connected. The symptoms would
start with one "long" HPD IRQ being detected at boot:

[    1.891398] [drm:intel_get_hpd_pins [i915]] hotplug event received, stat 0x00440000, dig 0x00440000, pins 0x000000a0
[    1.891436] [drm:intel_hpd_irq_handler [i915]] digital hpd port B - long
[    1.891472] [drm:intel_hpd_irq_handler [i915]] Received HPD interrupt on PIN 5 - cnt: 0
[    1.891508] [drm:intel_hpd_irq_handler [i915]] digital hpd port D - long
[    1.891544] [drm:intel_hpd_irq_handler [i915]] Received HPD interrupt on PIN 7 - cnt: 0
[    1.891592] [drm:intel_dp_hpd_pulse [i915]] got hpd irq on port B - long
[    1.891628] [drm:intel_dp_hpd_pulse [i915]] got hpd irq on port D - long
…

followed by constant short IRQs afterwards:

[    1.895091] [drm:intel_encoder_hotplug [i915]] [CONNECTOR:66:DP-1] status updated from unknown to disconnected
[    1.895129] [drm:i915_hotplug_work_func [i915]] Connector DP-3 (pin 7) received hotplug event.
[    1.895165] [drm:intel_dp_detect [i915]] [CONNECTOR:72:DP-3]
[    1.895275] [drm:intel_get_hpd_pins [i915]] hotplug event received, stat 0x00200000, dig 0x00200000, pins 0x00000080
[    1.895312] [drm:intel_hpd_irq_handler [i915]] digital hpd port D - short
[    1.895762] [drm:intel_get_hpd_pins [i915]] hotplug event received, stat 0x00200000, dig 0x00200000, pins 0x00000080
[    1.895799] [drm:intel_hpd_irq_handler [i915]] digital hpd port D - short
[    1.896239] [drm:intel_dp_aux_xfer [i915]] dp_aux_ch timeout status 0x71450085
[    1.896293] [drm:intel_get_hpd_pins [i915]] hotplug event received, stat 0x00200000, dig 0x00200000, pins 0x00000080
[    1.896330] [drm:intel_hpd_irq_handler [i915]] digital hpd port D - short
[    1.896781] [drm:intel_get_hpd_pins [i915]] hotplug event received, stat 0x00200000, dig 0x00200000, pins 0x00000080
[    1.896817] [drm:intel_hpd_irq_handler [i915]] digital hpd port D - short
[    1.897275] [drm:intel_get_hpd_pins [i915]] hotplug event received, stat 0x00200000, dig 0x00200000, pins 0x00000080

The customer's system in question has a GM45 GPU, which is apparently
well known for hotplugging storms.

So, workaround this impressively broken hardware by changing the default
HPD storm threshold from 5 to 50. Then, make long IRQs count for 10, and
short IRQs count for 1. This makes it so that 5 long IRQs will trigger
an HPD storm, and on systems with short HPD storm detection 50 short
IRQs will trigger an HPD storm. 50 short IRQs amounts to 100ms of
constant pulsing, which seems like a good middleground between being too
sensitive and not being sensitive enough (which would cause visible
stutters in userspace every time a storm occurs).

And just to be extra safe: we don't enable this by default on systems
with MST support. There's too high of a chance of MST support triggering
storm detection, and systems that are new enough to support MST are a
lot less likely to have issues with IRQ storms anyway.

As a note: this patch was tested using a ThinkPad T450s and a Chamelium
to simulate the short IRQ storms.

Changes since v1:
- Don't use two separate thresholds, just make long IRQs count for 10
  each and short IRQs count for 1. This simplifies the code a bit
  - Ville Syrjälä
Changes since v2:
- Document @long_hpd in intel_hpd_irq_storm_detect, no functional
  changes

Signed-off-by: Lyude Paul <lyude@redhat.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
---
 drivers/gpu/drm/i915/i915_debugfs.c  | 74 ++++++++++++++++++++++++++++
 drivers/gpu/drm/i915/i915_drv.h      |  5 +-
 drivers/gpu/drm/i915/i915_irq.c      |  7 +++
 drivers/gpu/drm/i915/intel_hotplug.c | 49 ++++++++++--------
 4 files changed, 114 insertions(+), 21 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index f60485906f7e..670db5073d70 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -4658,6 +4658,79 @@ static const struct file_operations i915_hpd_storm_ctl_fops = {
 	.write = i915_hpd_storm_ctl_write
 };
 
+static int i915_hpd_short_storm_ctl_show(struct seq_file *m, void *data)
+{
+	struct drm_i915_private *dev_priv = m->private;
+
+	seq_printf(m, "Enabled: %s\n",
+		   yesno(dev_priv->hotplug.hpd_short_storm_enabled));
+
+	return 0;
+}
+
+static int
+i915_hpd_short_storm_ctl_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, i915_hpd_short_storm_ctl_show,
+			   inode->i_private);
+}
+
+static ssize_t i915_hpd_short_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;
+	char *newline;
+	char tmp[16];
+	int i;
+	bool new_state;
+
+	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';
+
+	/* Reset to the "default" state for this system */
+	if (strcmp(tmp, "reset") == 0)
+		new_state = !HAS_DP_MST(dev_priv);
+	else if (kstrtobool(tmp, &new_state) != 0)
+		return -EINVAL;
+
+	DRM_DEBUG_KMS("%sabling HPD short storm detection\n",
+		      new_state ? "En" : "Dis");
+
+	spin_lock_irq(&dev_priv->irq_lock);
+	hotplug->hpd_short_storm_enabled = new_state;
+	/* 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 const struct file_operations i915_hpd_short_storm_ctl_fops = {
+	.owner = THIS_MODULE,
+	.open = i915_hpd_short_storm_ctl_open,
+	.read = seq_read,
+	.llseek = seq_lseek,
+	.release = single_release,
+	.write = i915_hpd_short_storm_ctl_write,
+};
+
 static int i915_drrs_ctl_set(void *data, u64 val)
 {
 	struct drm_i915_private *dev_priv = data;
@@ -4865,6 +4938,7 @@ static const struct i915_debugfs_files {
 	{"i915_guc_log_level", &i915_guc_log_level_fops},
 	{"i915_guc_log_relay", &i915_guc_log_relay_fops},
 	{"i915_hpd_storm_ctl", &i915_hpd_storm_ctl_fops},
+	{"i915_hpd_short_storm_ctl", &i915_hpd_short_storm_ctl_fops},
 	{"i915_ipc_status", &i915_ipc_status_fops},
 	{"i915_drrs_ctl", &i915_drrs_ctl_fops},
 	{"i915_edp_psr_debug", &i915_edp_psr_debug_fops}
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 2a88a7eb871b..0c8438de3c1b 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -283,7 +283,8 @@ 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
+/* Threshold == 5 for long IRQs, 50 for short */
+#define HPD_STORM_DEFAULT_THRESHOLD 50
 
 struct i915_hotplug {
 	struct work_struct hotplug_work;
@@ -308,6 +309,8 @@ struct i915_hotplug {
 	bool poll_enabled;
 
 	unsigned int hpd_storm_threshold;
+	/* Whether or not to count short HPD IRQs in HPD storms */
+	u8 hpd_short_storm_enabled;
 
 	/*
 	 * if we get a HPD irq from DP and a HPD irq from non-DP
diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index 5d1f53723388..d7e47d6082de 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -4863,6 +4863,13 @@ void intel_irq_init(struct drm_i915_private *dev_priv)
 		dev_priv->display_irqs_enabled = false;
 
 	dev_priv->hotplug.hpd_storm_threshold = HPD_STORM_DEFAULT_THRESHOLD;
+	/* If we have MST support, we want to avoid doing short HPD IRQ storm
+	 * detection, as short HPD storms will occur as a natural part of
+	 * sideband messaging with MST.
+	 * On older platforms however, IRQ storms can occur with both long and
+	 * short pulses, as seen on some G4x systems.
+	 */
+	dev_priv->hotplug.hpd_short_storm_enabled = !HAS_DP_MST(dev_priv);
 
 	dev->driver->get_vblank_timestamp = drm_calc_vbltimestamp_from_scanoutpos;
 	dev->driver->get_scanout_position = i915_get_crtc_scanoutpos;
diff --git a/drivers/gpu/drm/i915/intel_hotplug.c b/drivers/gpu/drm/i915/intel_hotplug.c
index d642c0795452..f10e72496ae1 100644
--- a/drivers/gpu/drm/i915/intel_hotplug.c
+++ b/drivers/gpu/drm/i915/intel_hotplug.c
@@ -114,34 +114,46 @@ enum hpd_pin intel_hpd_pin_default(struct drm_i915_private *dev_priv,
 #define HPD_STORM_REENABLE_DELAY	(2 * 60 * 1000)
 
 /**
- * intel_hpd_irq_storm_detect - gather stats and detect HPD irq storm on a pin
+ * 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
+ * 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
+ * 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.
+ * @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.
+ * 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)
+				       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)
+	if (!threshold ||
+	    (!long_hpd && !dev_priv->hotplug.hpd_short_storm_enabled))
 		return false;
 
 	if (!time_in_range(jiffies, start, end)) {
@@ -149,7 +161,8 @@ static bool intel_hpd_irq_storm_detect(struct drm_i915_private *dev_priv,
 		hpd->stats[pin].count = 0;
 	}
 
-	if (++hpd->stats[pin].count > threshold) {
+	hpd->stats[pin].count += increment;
+	if (hpd->stats[pin].count > threshold) {
 		hpd->stats[pin].state = HPD_MARK_DISABLED;
 		DRM_DEBUG_KMS("HPD interrupt storm detected on PIN %d\n", pin);
 		storm = true;
@@ -409,28 +422,24 @@ void intel_hpd_irq_handler(struct drm_i915_private *dev_priv,
 	for_each_intel_encoder(&dev_priv->drm, encoder) {
 		enum hpd_pin pin = encoder->hpd_pin;
 		bool has_hpd_pulse = intel_encoder_has_hpd_pulse(encoder);
+		bool long_hpd = true;
 
 		if (!(BIT(pin) & pin_mask))
 			continue;
 
 		if (has_hpd_pulse) {
-			bool long_hpd = long_mask & BIT(pin);
 			enum port port = encoder->port;
 
+			long_hpd = !!(long_mask & BIT(pin));
+
 			DRM_DEBUG_DRIVER("digital hpd port %c - %s\n", port_name(port),
 					 long_hpd ? "long" : "short");
-			/*
-			 * For long HPD pulses we want to have the digital queue happen,
-			 * but we still want HPD storm detection to function.
-			 */
 			queue_dig = true;
-			if (long_hpd) {
+			if (long_hpd)
 				dev_priv->hotplug.long_port_mask |= (1 << port);
-			} else {
-				/* for short HPD just trigger the digital queue */
+			else
 				dev_priv->hotplug.short_port_mask |= (1 << port);
-				continue;
-			}
+
 		}
 
 		if (dev_priv->hotplug.stats[pin].state == HPD_DISABLED) {
@@ -453,7 +462,7 @@ void intel_hpd_irq_handler(struct drm_i915_private *dev_priv,
 			queue_hp = true;
 		}
 
-		if (intel_hpd_irq_storm_detect(dev_priv, pin)) {
+		if (intel_hpd_irq_storm_detect(dev_priv, pin, long_hpd)) {
 			dev_priv->hotplug.event_bits &= ~BIT(pin);
 			storm_detected = true;
 		}
-- 
2.19.1

Re: [PATCH v4 5/5] drm/i915: Add short HPD IRQ storm detection for non-MST systems

[Ville Syrjälä]

On Mon, Nov 05, 2018 at 05:20:11PM -0500, Lyude Paul wrote:
> Unfortunately, it seems that the HPD IRQ storm problem from the early
> days of Intel GPUs was never entirely solved, only mostly. Within the
> last couple of days, I got a bug report from one of our customers who
> had been having issues with their machine suddenly booting up very
> slowly after having updated. The amount of time it took to boot went
> from around 30 seconds, to over 6 minutes consistently.
> 
> After some investigation, I discovered that i915 was reporting massive
> amounts of short HPD IRQ spam on this system from the DisplayPort port,
> despite there not being anything actually connected. The symptoms would
> start with one "long" HPD IRQ being detected at boot:
> 
> [    1.891398] [drm:intel_get_hpd_pins [i915]] hotplug event received, stat 0x00440000, dig 0x00440000, pins 0x000000a0
> [    1.891436] [drm:intel_hpd_irq_handler [i915]] digital hpd port B - long
> [    1.891472] [drm:intel_hpd_irq_handler [i915]] Received HPD interrupt on PIN 5 - cnt: 0
> [    1.891508] [drm:intel_hpd_irq_handler [i915]] digital hpd port D - long
> [    1.891544] [drm:intel_hpd_irq_handler [i915]] Received HPD interrupt on PIN 7 - cnt: 0
> [    1.891592] [drm:intel_dp_hpd_pulse [i915]] got hpd irq on port B - long
> [    1.891628] [drm:intel_dp_hpd_pulse [i915]] got hpd irq on port D - long
> …
> 
> followed by constant short IRQs afterwards:
> 
> [    1.895091] [drm:intel_encoder_hotplug [i915]] [CONNECTOR:66:DP-1] status updated from unknown to disconnected
> [    1.895129] [drm:i915_hotplug_work_func [i915]] Connector DP-3 (pin 7) received hotplug event.
> [    1.895165] [drm:intel_dp_detect [i915]] [CONNECTOR:72:DP-3]
> [    1.895275] [drm:intel_get_hpd_pins [i915]] hotplug event received, stat 0x00200000, dig 0x00200000, pins 0x00000080
> [    1.895312] [drm:intel_hpd_irq_handler [i915]] digital hpd port D - short
> [    1.895762] [drm:intel_get_hpd_pins [i915]] hotplug event received, stat 0x00200000, dig 0x00200000, pins 0x00000080
> [    1.895799] [drm:intel_hpd_irq_handler [i915]] digital hpd port D - short
> [    1.896239] [drm:intel_dp_aux_xfer [i915]] dp_aux_ch timeout status 0x71450085
> [    1.896293] [drm:intel_get_hpd_pins [i915]] hotplug event received, stat 0x00200000, dig 0x00200000, pins 0x00000080
> [    1.896330] [drm:intel_hpd_irq_handler [i915]] digital hpd port D - short
> [    1.896781] [drm:intel_get_hpd_pins [i915]] hotplug event received, stat 0x00200000, dig 0x00200000, pins 0x00000080
> [    1.896817] [drm:intel_hpd_irq_handler [i915]] digital hpd port D - short
> [    1.897275] [drm:intel_get_hpd_pins [i915]] hotplug event received, stat 0x00200000, dig 0x00200000, pins 0x00000080
> 
> The customer's system in question has a GM45 GPU, which is apparently
> well known for hotplugging storms.
> 
> So, workaround this impressively broken hardware by changing the default
> HPD storm threshold from 5 to 50. Then, make long IRQs count for 10, and
> short IRQs count for 1. This makes it so that 5 long IRQs will trigger
> an HPD storm, and on systems with short HPD storm detection 50 short
> IRQs will trigger an HPD storm. 50 short IRQs amounts to 100ms of
> constant pulsing, which seems like a good middleground between being too
> sensitive and not being sensitive enough (which would cause visible
> stutters in userspace every time a storm occurs).
> 
> And just to be extra safe: we don't enable this by default on systems
> with MST support. There's too high of a chance of MST support triggering
> storm detection, and systems that are new enough to support MST are a
> lot less likely to have issues with IRQ storms anyway.
> 
> As a note: this patch was tested using a ThinkPad T450s and a Chamelium
> to simulate the short IRQ storms.
> 
> Changes since v1:
> - Don't use two separate thresholds, just make long IRQs count for 10
>   each and short IRQs count for 1. This simplifies the code a bit
>   - Ville Syrjälä
> Changes since v2:
> - Document @long_hpd in intel_hpd_irq_storm_detect, no functional
>   changes
> 
> Signed-off-by: Lyude Paul <lyude@redhat.com>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
> ---
>  drivers/gpu/drm/i915/i915_debugfs.c  | 74 ++++++++++++++++++++++++++++
>  drivers/gpu/drm/i915/i915_drv.h      |  5 +-
>  drivers/gpu/drm/i915/i915_irq.c      |  7 +++
>  drivers/gpu/drm/i915/intel_hotplug.c | 49 ++++++++++--------
>  4 files changed, 114 insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> index f60485906f7e..670db5073d70 100644
> --- a/drivers/gpu/drm/i915/i915_debugfs.c
> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> @@ -4658,6 +4658,79 @@ static const struct file_operations i915_hpd_storm_ctl_fops = {
>  	.write = i915_hpd_storm_ctl_write
>  };
>  
> +static int i915_hpd_short_storm_ctl_show(struct seq_file *m, void *data)
> +{
> +	struct drm_i915_private *dev_priv = m->private;
> +
> +	seq_printf(m, "Enabled: %s\n",
> +		   yesno(dev_priv->hotplug.hpd_short_storm_enabled));
> +
> +	return 0;
> +}
> +
> +static int
> +i915_hpd_short_storm_ctl_open(struct inode *inode, struct file *file)
> +{
> +	return single_open(file, i915_hpd_short_storm_ctl_show,
> +			   inode->i_private);
> +}
> +
> +static ssize_t i915_hpd_short_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;
> +	char *newline;
> +	char tmp[16];
> +	int i;
> +	bool new_state;
> +
> +	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';
> +
> +	/* Reset to the "default" state for this system */
> +	if (strcmp(tmp, "reset") == 0)
> +		new_state = !HAS_DP_MST(dev_priv);
> +	else if (kstrtobool(tmp, &new_state) != 0)
> +		return -EINVAL;
> +
> +	DRM_DEBUG_KMS("%sabling HPD short storm detection\n",
> +		      new_state ? "En" : "Dis");
> +
> +	spin_lock_irq(&dev_priv->irq_lock);
> +	hotplug->hpd_short_storm_enabled = new_state;
> +	/* 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 const struct file_operations i915_hpd_short_storm_ctl_fops = {
> +	.owner = THIS_MODULE,
> +	.open = i915_hpd_short_storm_ctl_open,
> +	.read = seq_read,
> +	.llseek = seq_lseek,
> +	.release = single_release,
> +	.write = i915_hpd_short_storm_ctl_write,
> +};
> +
>  static int i915_drrs_ctl_set(void *data, u64 val)
>  {
>  	struct drm_i915_private *dev_priv = data;
> @@ -4865,6 +4938,7 @@ static const struct i915_debugfs_files {
>  	{"i915_guc_log_level", &i915_guc_log_level_fops},
>  	{"i915_guc_log_relay", &i915_guc_log_relay_fops},
>  	{"i915_hpd_storm_ctl", &i915_hpd_storm_ctl_fops},
> +	{"i915_hpd_short_storm_ctl", &i915_hpd_short_storm_ctl_fops},
>  	{"i915_ipc_status", &i915_ipc_status_fops},
>  	{"i915_drrs_ctl", &i915_drrs_ctl_fops},
>  	{"i915_edp_psr_debug", &i915_edp_psr_debug_fops}
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 2a88a7eb871b..0c8438de3c1b 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -283,7 +283,8 @@ 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
> +/* Threshold == 5 for long IRQs, 50 for short */
> +#define HPD_STORM_DEFAULT_THRESHOLD 50
>  
>  struct i915_hotplug {
>  	struct work_struct hotplug_work;
> @@ -308,6 +309,8 @@ struct i915_hotplug {
>  	bool poll_enabled;
>  
>  	unsigned int hpd_storm_threshold;
> +	/* Whether or not to count short HPD IRQs in HPD storms */
> +	u8 hpd_short_storm_enabled;
>  
>  	/*
>  	 * if we get a HPD irq from DP and a HPD irq from non-DP
> diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
> index 5d1f53723388..d7e47d6082de 100644
> --- a/drivers/gpu/drm/i915/i915_irq.c
> +++ b/drivers/gpu/drm/i915/i915_irq.c
> @@ -4863,6 +4863,13 @@ void intel_irq_init(struct drm_i915_private *dev_priv)
>  		dev_priv->display_irqs_enabled = false;
>  
>  	dev_priv->hotplug.hpd_storm_threshold = HPD_STORM_DEFAULT_THRESHOLD;
> +	/* If we have MST support, we want to avoid doing short HPD IRQ storm
> +	 * detection, as short HPD storms will occur as a natural part of
> +	 * sideband messaging with MST.
> +	 * On older platforms however, IRQ storms can occur with both long and
> +	 * short pulses, as seen on some G4x systems.
> +	 */
> +	dev_priv->hotplug.hpd_short_storm_enabled = !HAS_DP_MST(dev_priv);
>  
>  	dev->driver->get_vblank_timestamp = drm_calc_vbltimestamp_from_scanoutpos;
>  	dev->driver->get_scanout_position = i915_get_crtc_scanoutpos;
> diff --git a/drivers/gpu/drm/i915/intel_hotplug.c b/drivers/gpu/drm/i915/intel_hotplug.c
> index d642c0795452..f10e72496ae1 100644
> --- a/drivers/gpu/drm/i915/intel_hotplug.c
> +++ b/drivers/gpu/drm/i915/intel_hotplug.c
> @@ -114,34 +114,46 @@ enum hpd_pin intel_hpd_pin_default(struct drm_i915_private *dev_priv,
>  #define HPD_STORM_REENABLE_DELAY	(2 * 60 * 1000)
>  
>  /**
> - * intel_hpd_irq_storm_detect - gather stats and detect HPD irq storm on a pin
> + * 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
> + * 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
> + * 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.
> + * @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.
> + * 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)
> +				       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)
> +	if (!threshold ||
> +	    (!long_hpd && !dev_priv->hotplug.hpd_short_storm_enabled))
>  		return false;
>  
>  	if (!time_in_range(jiffies, start, end)) {
> @@ -149,7 +161,8 @@ static bool intel_hpd_irq_storm_detect(struct drm_i915_private *dev_priv,
>  		hpd->stats[pin].count = 0;
>  	}
>  
> -	if (++hpd->stats[pin].count > threshold) {
> +	hpd->stats[pin].count += increment;
> +	if (hpd->stats[pin].count > threshold) {
>  		hpd->stats[pin].state = HPD_MARK_DISABLED;
>  		DRM_DEBUG_KMS("HPD interrupt storm detected on PIN %d\n", pin);
>  		storm = true;
> @@ -409,28 +422,24 @@ void intel_hpd_irq_handler(struct drm_i915_private *dev_priv,
>  	for_each_intel_encoder(&dev_priv->drm, encoder) {
>  		enum hpd_pin pin = encoder->hpd_pin;
>  		bool has_hpd_pulse = intel_encoder_has_hpd_pulse(encoder);
> +		bool long_hpd = true;
>  
>  		if (!(BIT(pin) & pin_mask))
>  			continue;
>  
>  		if (has_hpd_pulse) {
> -			bool long_hpd = long_mask & BIT(pin);
>  			enum port port = encoder->port;
>  
> +			long_hpd = !!(long_mask & BIT(pin));
> +

!! not needed

>  			DRM_DEBUG_DRIVER("digital hpd port %c - %s\n", port_name(port),
>  					 long_hpd ? "long" : "short");
> -			/*
> -			 * For long HPD pulses we want to have the digital queue happen,
> -			 * but we still want HPD storm detection to function.
> -			 */
>  			queue_dig = true;
> -			if (long_hpd) {
> +			if (long_hpd)
>  				dev_priv->hotplug.long_port_mask |= (1 << port);
> -			} else {
> -				/* for short HPD just trigger the digital queue */
> +			else
>  				dev_priv->hotplug.short_port_mask |= (1 << port);
> -				continue;
> -			}
> +
>  		}
>  
>  		if (dev_priv->hotplug.stats[pin].state == HPD_DISABLED) {
> @@ -453,7 +462,7 @@ void intel_hpd_irq_handler(struct drm_i915_private *dev_priv,
>  			queue_hp = true;
>  		}
>  
> -		if (intel_hpd_irq_storm_detect(dev_priv, pin)) {
> +		if (intel_hpd_irq_storm_detect(dev_priv, pin, long_hpd)) {
>  			dev_priv->hotplug.event_bits &= ~BIT(pin);
>  			storm_detected = true;

queue_hp = true ?

>  		}
> -- 
> 2.19.1

-- 
Ville Syrjälä
Intel