5.4-stable review patch. If anyone has any objections, please let me know.
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From: Lad Prabhakar prabhakar.mahadev-lad.rj@bp.renesas.com
commit 706136c5723626fcde8dd8f598a4dcd251e24927 upstream.
Add a final dma_wmb() barrier before triggering the transmit request (TCCR_TSRQ) to ensure all descriptor and buffer writes are visible to the DMA engine.
According to the hardware manual, a read-back operation is required before writing to the doorbell register to guarantee completion of previous writes. Instead of performing a dummy read, a dma_wmb() is used to both enforce the same ordering semantics on the CPU side and also to ensure completion of writes.
Fixes: c156633f1353 ("Renesas Ethernet AVB driver proper") Cc: stable@vger.kernel.org Co-developed-by: Fabrizio Castro fabrizio.castro.jz@renesas.com Signed-off-by: Fabrizio Castro fabrizio.castro.jz@renesas.com Signed-off-by: Lad Prabhakar prabhakar.mahadev-lad.rj@bp.renesas.com Reviewed-by: Niklas Söderlund niklas.soderlund+renesas@ragnatech.se Link: https://patch.msgid.link/20251017151830.171062-5-prabhakar.mahadev-lad.rj@bp... Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/net/ethernet/renesas/ravb_main.c | 8 ++++++++ 1 file changed, 8 insertions(+)
--- a/drivers/net/ethernet/renesas/ravb_main.c +++ b/drivers/net/ethernet/renesas/ravb_main.c @@ -1602,6 +1602,14 @@ static netdev_tx_t ravb_start_xmit(struc } else { desc->die_dt = DT_FSINGLE; } + + /* Before ringing the doorbell we need to make sure that the latest + * writes have been committed to memory, otherwise it could delay + * things until the doorbell is rang again. + * This is in replacement of the read operation mentioned in the HW + * manuals. + */ + dma_wmb(); ravb_modify(ndev, TCCR, TCCR_TSRQ0 << q, TCCR_TSRQ0 << q);
priv->cur_tx[q] += num_tx_desc;