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diff --git a/sys/dev/mlx5/mlx5_en/mlx5_en_main.c b/sys/dev/mlx5/mlx5_en/mlx5_en_main.c
--- a/sys/dev/mlx5/mlx5_en/mlx5_en_main.c
+++ b/sys/dev/mlx5/mlx5_en/mlx5_en_main.c
@@ -1134,6 +1134,25 @@
return (((uint64_t)hw_h << 32) | hw_l);
}
+/*
+ * Seed the first calibration point so that base_prev and clbr_hw_prev
+ * are always valid. Called once during attach before the first
+ * calibration callout fires.
+ */
+static void
+mlx5e_seed_calibration(struct mlx5e_priv *priv)
+{
+ struct mlx5e_clbr_point *cp;
+ struct timespec ts;
+
+ cp = &priv->clbr_points[0];
+ cp->clbr_hw_curr = mlx5e_hw_clock(priv);
+ nanouptime(&ts);
+ cp->base_curr = mlx5e_timespec2usec(&ts);
+ cp->clbr_hw_prev = cp->clbr_hw_curr - 1;
+ cp->base_prev = cp->base_curr - 1;
+}
+
/*
* The calibration callout, it runs either in the context of the
* thread which enables calibration, or in callout. It takes the
@@ -1147,6 +1166,9 @@
struct mlx5e_priv *priv;
struct mlx5e_clbr_point *next, *curr;
struct timespec ts;
+ uint64_t hw_delta_new, hw_delta_old;
+ uint64_t old_nsec, old_projected, old_sec;
+ uint64_t res_n, res_s, res_s_mod, rt_delta_old;
int clbr_curr_next;
priv = arg;
@@ -1175,6 +1197,33 @@
nanouptime(&ts);
next->base_curr = mlx5e_timespec2usec(&ts);
+ /*
+ * Ensure monotonicity across calibration transitions. Compute
+ * what the old calibration would extrapolate to at the new
+ * hw_curr. If the new base_curr is less, clamp it so the new
+ * slope is at least as steep as the old one. This prevents
+ * packets from seeing time go backwards when the slope drops.
+ *
+ * Use the same split-seconds technique as mlx5e_mbuf_tstmp()
+ * to avoid overflowing uint64_t in the multiplication.
+ */
+ hw_delta_new = next->clbr_hw_curr - curr->clbr_hw_curr;
+ rt_delta_old = curr->base_curr - curr->base_prev;
+ hw_delta_old = curr->clbr_hw_curr - curr->clbr_hw_prev;
+ old_sec = hw_delta_new / priv->cclk;
+ old_nsec = hw_delta_new % priv->cclk;
+ res_s = old_sec * rt_delta_old;
+ res_n = old_nsec * rt_delta_old;
+ res_s_mod = res_s % hw_delta_old;
+ res_s /= hw_delta_old;
+ res_s_mod *= priv->cclk;
+ res_n += res_s_mod;
+ res_n /= hw_delta_old;
+ res_s *= priv->cclk;
+ old_projected = curr->base_curr + res_s + res_n;
+ if (next->base_curr < old_projected)
+ next->base_curr = old_projected;
+
curr->clbr_gen = 0;
atomic_thread_fence_rel();
priv->clbr_curr = clbr_curr_next;
@@ -4887,6 +4936,7 @@
callout_init(&priv->tstmp_clbr, 1);
/* Pull out the frequency of the clock in hz */
priv->cclk = (uint64_t)MLX5_CAP_GEN(mdev, device_frequency_khz) * 1000ULL;
+ mlx5e_seed_calibration(priv);
mlx5e_reset_calibration_callout(priv);
pa.pa_version = PFIL_VERSION;

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