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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , linux-kernel@vger.kernel.org (open list) Subject: [PATCHv2 net-next] net: ibm: emac: Clear MAL descriptors without memset Date: Wed, 3 Jun 2026 15:17:56 -0700 Message-ID: <20260603221756.56203-1-rosenp@gmail.com> X-Mailer: git-send-email 2.54.0 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Clear MAL descriptor rings with explicit field stores instead of memset(). The descriptor rings are carved from MAL coherent DMA memory, which may be mapped uncached on 32-bit powerpc. The optimized memset() path can use dcbz there and trigger an alignment warning. Use WRITE_ONCE() for each field to prevent the compiler from merging the stores back into a memset() call. The skb tracking arrays remain ordinary CPU memory and still use memset(). Assisted-by: Codex:GPT-5.5 Signed-off-by: Rosen Penev --- v2: Use WRITE_ONCE drivers/net/ethernet/ibm/emac/core.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) diff --git a/drivers/net/ethernet/ibm/emac/core.c b/drivers/net/ethernet/ibm/emac/core.c index d2194b406c9e..b7568d96aa47 100644 --- a/drivers/net/ethernet/ibm/emac/core.c +++ b/drivers/net/ethernet/ibm/emac/core.c @@ -1162,6 +1162,17 @@ static void emac_clean_rx_ring(struct emac_instance *dev) } } +static void emac_clear_mal_desc(struct mal_descriptor *desc, int count) +{ + int i; + + for (i = 0; i < count; i++) { + WRITE_ONCE(desc[i].ctrl, 0); + WRITE_ONCE(desc[i].data_len, 0); + WRITE_ONCE(desc[i].data_ptr, 0); + } +} + static int __emac_prepare_rx_skb(struct sk_buff *skb, struct emac_instance *dev, int slot) { @@ -3089,8 +3100,8 @@ static int emac_probe(struct platform_device *ofdev) DBG(dev, "rx_desc %p" NL, dev->rx_desc); /* Clean rings */ - memset(dev->tx_desc, 0, NUM_TX_BUFF * sizeof(struct mal_descriptor)); - memset(dev->rx_desc, 0, NUM_RX_BUFF * sizeof(struct mal_descriptor)); + emac_clear_mal_desc(dev->tx_desc, NUM_TX_BUFF); + emac_clear_mal_desc(dev->rx_desc, NUM_RX_BUFF); memset(dev->tx_skb, 0, NUM_TX_BUFF * sizeof(struct sk_buff *)); memset(dev->rx_skb, 0, NUM_RX_BUFF * sizeof(struct sk_buff *)); -- 2.54.0