[PATCH 1/2] thunderbolt: drop start_poll guard in tb_ring_poll_complete()

[Benjamin Berman <benjamin.s.berman@gmail.com>]

Under concurrent load on a single NHI with several rings simultaneously
in NAPI poll (e.g. a Maple Ridge TB4 transit forwarding tbnet traffic
between two peers), one ring's interrupt enable bit in
REG_RING_INTERRUPT_BASE can stay cleared.  MSI-X stops for that ring,
NAPI is never rescheduled, but carrier is reported up and no driver
event fires.  The ring stays masked until thunderbolt_net is reloaded.

tb_ring_poll_complete() gated the unmask on @start_poll:

	if (ring->start_poll)
		__ring_interrupt_mask(ring, false);

while the ISR path masks unconditionally via __ring_interrupt().  In a
window where @start_poll is observed as NULL by the unmask path while
the paired mask persists, the ring is left permanently masked.

Gate on @running instead and add an ioread32() barrier so the posted
enable reaches the device before the spinlock is dropped.

On NHIs without QUIRK_AUTO_CLEAR_INT a second issue compounds the
first: stale pending status in REG_RING_NOTIFY_BASE can prevent the
hardware from re-arming its MSI-X generator when the ring is
re-enabled.  Clear the ring's bit in REG_RING_INT_CLEAR before setting
the enable bit, mirroring what ring_msix() already does at ISR entry.

Verified on a Maple Ridge 4C transit and two TB3 Titan Ridge endpoints
running NCCL all-reduce over tb-lo: pre-patch the chain wedges in
under 1 GB; post-patch a 192 GB run (3000 iterations of a 64 MiB
all-reduce) completes with mask/unmask counters balanced.

Generated-by: Claude Opus 4.7 <claude-opus-4-7@anthropic.com>
Tested-by: Benjamin Berman <benjamin.s.berman@gmail.com>
Signed-off-by: Benjamin Berman <benjamin.s.berman@gmail.com>
---
 drivers/thunderbolt/nhi.c | 22 +++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/drivers/thunderbolt/nhi.c b/drivers/thunderbolt/nhi.c
index 2bb2e79ca..bba45ec36 100644
--- a/drivers/thunderbolt/nhi.c
+++ b/drivers/thunderbolt/nhi.c
@@ -389,10 +389,24 @@ static void __ring_interrupt_mask(struct tb_ring *ring, bool mask)
 	u32 val;
 
 	val = ioread32(ring->nhi->iobase + reg);
-	if (mask)
+	if (mask) {
 		val &= ~BIT(bit);
-	else
+	} else {
+		if (!(ring->nhi->quirks & QUIRK_AUTO_CLEAR_INT)) {
+			int cbit = ring_interrupt_index(ring) & 31;
+
+			if (ring->is_tx)
+				iowrite32(BIT(cbit),
+					  ring->nhi->iobase +
+					  REG_RING_INT_CLEAR);
+			else
+				iowrite32(BIT(cbit),
+					  ring->nhi->iobase +
+					  REG_RING_INT_CLEAR +
+					  4 * (ring->nhi->hop_count / 32));
+		}
 		val |= BIT(bit);
+	}
 	iowrite32(val, ring->nhi->iobase + reg);
 }
 
@@ -423,8 +437,10 @@ void tb_ring_poll_complete(struct tb_ring *ring)
 
 	spin_lock_irqsave(&ring->nhi->lock, flags);
 	spin_lock(&ring->lock);
-	if (ring->start_poll)
+	if (ring->running) {
 		__ring_interrupt_mask(ring, false);
+		(void)ioread32(ring->nhi->iobase + REG_RING_INTERRUPT_BASE);
+	}
 	spin_unlock(&ring->lock);
 	spin_unlock_irqrestore(&ring->nhi->lock, flags);
 }
-- 
2.43.0