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([2401:4900:1c07:c7d3:fdc9:5e8f:28db:7f80]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2909930a756sm67193955ad.14.2025.10.17.08.19.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 17 Oct 2025 08:19:51 -0700 (PDT) From: Prabhakar X-Google-Original-From: Prabhakar To: =?UTF-8?q?Niklas=20S=C3=B6derlund?= , Paul Barker , Andrew Lunn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Geert Uytterhoeven , Mitsuhiro Kimura Cc: netdev@vger.kernel.org, linux-renesas-soc@vger.kernel.org, linux-kernel@vger.kernel.org, Prabhakar , Biju Das , Fabrizio Castro , Lad Prabhakar , stable@vger.kernel.org Subject: [PATCH v2 4/4] net: ravb: Ensure memory write completes before ringing TX doorbell Date: Fri, 17 Oct 2025 16:18:30 +0100 Message-ID: <20251017151830.171062-5-prabhakar.mahadev-lad.rj@bp.renesas.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20251017151830.171062-1-prabhakar.mahadev-lad.rj@bp.renesas.com> References: <20251017151830.171062-1-prabhakar.mahadev-lad.rj@bp.renesas.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Lad Prabhakar 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 Signed-off-by: Fabrizio Castro Signed-off-by: Lad Prabhakar Reviewed-by: Niklas S=C3=B6derlund --- 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/etherne= t/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 *s= kb, struct net_device *ndev) dma_wmb(); desc->die_dt =3D 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); =20 priv->cur_tx[q] +=3D num_tx_desc; --=20 2.43.0