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

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>