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net: ravb: Ensure memory write completes before ringing TX doorbell

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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: c156633f13 ("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.renesas.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Lad Prabhakar 2025-10-17 16:18:30 +01:00 • committed by Greg Kroah-Hartman
commit 14b68ab4f6
1 changed files with 8 additions and 0 deletions
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8
drivers/net/ethernet/renesas/ravb_main.c
View file

@ -1602,6 +1602,14 @@ static netdev_tx_t ravb_start_xmit(struct sk_buff *skb, struct net_device *ndev)
} 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;