net: ionic: add dma_wmb() before ringing TX doorbell

[ Upstream commit d261f5b09c28850dc63ca1d3018596f829f402d5 ]

The TX path currently writes descriptors and then immediately writes to
the MMIO doorbell register to notify the NIC.  On weakly ordered
architectures, descriptor writes may still be pending in CPU or DMA
write buffers when the doorbell is issued, leading to the device
fetching stale or incomplete descriptors.

Add a dma_wmb() in ionic_txq_post() to ensure all descriptor writes are
visible to the device before the doorbell MMIO write.

Fixes: 0f3154e6bcb3 ("ionic: Add Tx and Rx handling")
Signed-off-by: Mohammad Heib <mheib@redhat.com>
Link: https://patch.msgid.link/20251031155203.203031-1-mheib@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/net/ethernet/pensando/ionic/ionic_txrx.c b/drivers/net/ethernet/pensando/ionic/ionic_txrx.c
index 0f5758c273c2297a4e79716212a499d84494502c..3a094d3ea6f4f50d4b75e76858d58ce2c5f341d8 100644 (file)
--- a/drivers/net/ethernet/pensando/ionic/ionic_txrx.c
+++ b/drivers/net/ethernet/pensando/ionic/ionic_txrx.c
@@ -29,6 +29,10 @@ static void ionic_tx_clean(struct ionic_queue *q,
 
 static inline void ionic_txq_post(struct ionic_queue *q, bool ring_dbell)
 {
+       /* Ensure TX descriptor writes reach memory before NIC reads them.
+        * Prevents device from fetching stale descriptors.
+        */
+       dma_wmb();
        ionic_q_post(q, ring_dbell);
 }