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