From: Lad Prabhakar prabhakar.mahadev-lad.rj@bp.renesas.com
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 --- v1->v2: - New patch added to separate out the memory barrier change before ringing the doorbell. --- drivers/net/ethernet/renesas/ravb_main.c | 8 ++++++++ 1 file changed, 8 insertions(+)
diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c index 0e40001f64b4..c3fc15f9ec85 100644 --- a/drivers/net/ethernet/renesas/ravb_main.c +++ b/drivers/net/ethernet/renesas/ravb_main.c @@ -2232,6 +2232,14 @@ static netdev_tx_t ravb_start_xmit(struct sk_buff *skb, struct net_device *ndev) dma_wmb(); 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;
Hello Lad,
Thanks for your work.
On 2025-10-17 16:18:30 +0100, Prabhakar wrote:
From: Lad Prabhakar prabhakar.mahadev-lad.rj@bp.renesas.com
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
v1->v2:
- New patch added to separate out the memory barrier change before ringing the doorbell.
drivers/net/ethernet/renesas/ravb_main.c | 8 ++++++++ 1 file changed, 8 insertions(+)
diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c index 0e40001f64b4..c3fc15f9ec85 100644 --- a/drivers/net/ethernet/renesas/ravb_main.c +++ b/drivers/net/ethernet/renesas/ravb_main.c @@ -2232,6 +2232,14 @@ static netdev_tx_t ravb_start_xmit(struct sk_buff *skb, struct net_device *ndev) dma_wmb(); 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
nit: I would spell out hardware here, if you do a v3.
* manuals.*/- dma_wmb(); ravb_modify(ndev, TCCR, TCCR_TSRQ0 << q, TCCR_TSRQ0 << q);
priv->cur_tx[q] += num_tx_desc; -- 2.43.0
linux-stable-mirror@lists.linaro.org
-
Niklas Söderlund -
Prabhakar