From e9f5cfb561f7dc94b610e3130dfee9f3325d7d6d Mon Sep 17 00:00:00 2001
From: Arthur Hanson Rasmusson <arthur@vgpu.io>
Date: Sat, 24 Oct 2026 04:17:32 -0400
Subject: vgsp-gr r598 diag: peek the ring slots past GP_PUT at the launch
 decision

The r568 lever is the driver's ring WRITE pointer, not the GPFIFO put:
the b copy entry exists in the ring before the client publishes GP_PUT.
Add a bounded diagnostic (gsp_phys_gr_peek) that, when a channel reads
as drained, dumps up to four slots past last_get with {va,len} and
whether the slot already executed that exact entry - so the next fix can
be grounded in what is actually written ahead of the put.
---
 kernel/gsp_sema_service.c | 60 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)

(limited to 'kernel/gsp_sema_service.c')

diff --git a/kernel/gsp_sema_service.c b/kernel/gsp_sema_service.c
index f1a31df..65b8ac1 100644
--- a/kernel/gsp_sema_service.c
+++ b/kernel/gsp_sema_service.c
@@ -21148,6 +21148,65 @@ static bool svc_ce_stream_backlog(struct nv_vgpu_device *vgpu)
 	return false;
 }
 
+/*
+ * r598 diag: the driver's ring WRITE pointer, not the GPFIFO put. The r568
+ * draw needs the copy entries that are already written into the ring but
+ * whose GP_PUT has not been published yet. When the put says the ring is
+ * drained, peek at the slots immediately after the consumption position and
+ * log their {va,len} plus whether the slot already executed that exact
+ * entry. Bounded per launch, gated by gsp_phys_gr_peek.
+ */
+u32 gsp_phys_gr_peek;
+
+static void svc_gr_peek_lookahead(struct nv_vgpu_device *vgpu,
+				  const struct svc_channel *self)
+{
+	u32 k, logged = 0;
+
+	if (!gsp_phys_gr_peek || !svc_pass_local)
+		return;
+	for (k = 0; k < svc_pass_local_n && logged < 8; k++) {
+		const struct svc_channel *c = &svc_pass_local[k];
+		u32 put = 0, j;
+
+		if (!c->valid || c->h_object == self->h_object ||
+		    !c->gpfifo_va || !c->gpfifo_entries || !c->userd_pa)
+			continue;
+		if (svc_read_ap(vgpu, c->userd_pa + SVC_USERD_GP_PUT,
+				c->userd_as, &put, sizeof(put)))
+			continue;
+		put %= c->gpfifo_entries;
+		if (put != ((u32)c->last_get % c->gpfifo_entries))
+			continue;	/* real published backlog */
+		pr_info("vgsp-gr: peek h=0x%x put=%u last=%u\n",
+			c->h_object, put, (u32)c->last_get);
+		for (j = 1; j <= 4; j++) {
+			u32 idx = ((u32)c->last_get + j) % c->gpfifo_entries;
+			u8 ent[SVC_GPFIFO_ENTRY_SIZE];
+			u32 e0, e1, len;
+			u64 va;
+
+			if (svc_read_va(vgpu,
+					c->gpfifo_va +
+					(u64)idx * SVC_GPFIFO_ENTRY_SIZE,
+					ent, sizeof(ent)))
+				break;
+			memcpy(&e0, ent, 4);
+			memcpy(&e1, ent + 4, 4);
+			va = ((u64)(e1 & 0xff) << 32) |
+			     (u64)(e0 & 0xfffffffc);
+			len = ((e1 >> 10) & 0x1fffff) << 2;
+			if (!va || !len || len > SVC_PUSH_MAX)
+				break;
+			pr_info("vgsp-gr: peek   +%u idx=%u va=0x%llx len=%u ident_match=%d\n",
+				j, idx, va, len,
+				c->slot_ops_ident[idx] ==
+					((u64)e0 | ((u64)e1 << 32)));
+		}
+		logged++;
+	}
+}
+
 /*
  * r576 DIAG: the GR launch-decision witness (gsp_phys_gr_dec_log=N budget
  * per boot). Logged from svc_gr_request right after the fill, for launches
@@ -21401,6 +21460,7 @@ static bool svc_gr_request(struct nv_vgpu_device *vgpu,
 	 * historical forward stands (witnessed) - the guard delays a launch,
 	 * it never refuses one, so it cannot recreate r588's mail refusal.
 	 */
+	svc_gr_peek_lookahead(vgpu, ch);
 	if (svc_ce_stream_backlog(vgpu)) {
 		if (!svc_gr_defer_expired(svc_gr_cand.push_va)) {
 			clear_bit_unlock(SVC_FWD_INFLIGHT, &svc_fwd_state);
-- 
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