Message-ID: <20181106135046.GS9144@intel.com>
Date:   Tue, 6 Nov 2018 15:50:46 +0200
From:   Ville Syrjälä <ville.syrjala@...ux.intel.com>
To:     Lyude Paul <lyude@...hat.com>
Cc:     intel-gfx@...ts.freedesktop.org,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        David Airlie <airlied@...ux.ie>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 5/5] drm/i915: Add short HPD IRQ storm detection for
 non-MST systems

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@...hat.com>
> Cc: Ville Syrjälä <ville.syrjala@...ux.intel.com>
> Cc: Rodrigo Vivi <rodrigo.vivi@...el.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

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