On Fri, Oct 26, 2018 at 06:49:09PM -0400, 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
>
> Signed-off-by: Lyude Paul <lyude@xxxxxxxxxx>
> Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> ---
> 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 | 47 +++++++++++-------
> 4 files changed, 113 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> index b4744a68cd88..1595b8565875 100644
> --- a/drivers/gpu/drm/i915/i915_debugfs.c
> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> @@ -4641,6 +4641,79 @@ 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;
> @@ -4818,6 +4891,7 @@ 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 808204a7ca7c..a378e0fd2022 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -282,7 +282,8 @@ 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;
> @@ -307,6 +308,8 @@ 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 10f28a2ee2e6..57970b3a22df 100644
> --- a/drivers/gpu/drm/i915/i915_irq.c
> +++ b/drivers/gpu/drm/i915/i915_irq.c
> @@ -4843,6 +4843,13 @@ 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 8326900a311e..aa6f52e723f0 100644
> --- a/drivers/gpu/drm/i915/intel_hotplug.c
> +++ b/drivers/gpu/drm/i915/intel_hotplug.c
> @@ -114,32 +114,45 @@ 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
> *
> - * 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)
> {
> unsigned long start = dev_priv->hotplug.stats[pin].last_jiffies;
> unsigned long end = start + msecs_to_jiffies(HPD_STORM_DETECT_PERIOD);
> const int threshold = dev_priv->hotplug.hpd_storm_threshold;
> + const int increment = long_hpd ? 10 : 1;
> bool storm = false;
>
> + if (!long_hpd && !dev_priv->hotplug.hpd_short_storm_enabled)
> + return false;
> +
> if (!time_in_range(jiffies, start, end)) {
> dev_priv->hotplug.stats[pin].last_jiffies = jiffies;
> dev_priv->hotplug.stats[pin].count = 0;
> @@ -150,7 +163,7 @@ static bool intel_hpd_irq_storm_detect(struct drm_i915_private *dev_priv,
> DRM_DEBUG_KMS("HPD interrupt storm detected on PIN %d\n", pin);
> storm = true;
> } else {
> - dev_priv->hotplug.stats[pin].count++;
> + dev_priv->hotplug.stats[pin].count += increment;
> DRM_DEBUG_KMS("Received HPD interrupt on PIN %d - cnt: %d\n", pin,
> dev_priv->hotplug.stats[pin].count);
> }
> @@ -405,28 +418,24 @@ 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) {
> @@ -449,7 +458,7 @@ 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;
> }
Looks like we won't actually disable the hpd irq anywhere. Even the
current long hpd storm handling seems a bit confused as it will
call .hpd_irq_setup() from intel_hpd_irq_handler() but actually
marking the pins as disabled won't happen until
i915_hotplug_work_func(). So the interrupt won't actually get disabled
until the second time through intel_hpd_irq_handler() after we detected
a storm.
--
Ville Syrjälä
Intel
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