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Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1x4jjJ-0000000FAg9-2Wpr; Thu, 10 Sep 2026 18:42:37 +0000 Received: from mail.tipi-net.de ([2a03:4000:43:185::1]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1x4jjH-0000000FAfd-0mQ1 for linux-arm-kernel@lists.infradead.org; Thu, 10 Sep 2026 18:42:36 +0000 Received: from [127.0.0.1] (localhost [127.0.0.1]) by localhost (Mailerdaemon) with ESMTPSA id E2234A8F56; Thu, 10 Sep 2026 20:42:22 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=tipi-net.de; s=dkim; t=1789065751; h=from:subject:date:message-id:to:cc:mime-version:content-type: content-transfer-encoding:in-reply-to:references; bh=J6vYeDOQvc6HcH8O/wl4zA/DD/Gh7wd3PXwiCbaa1Cs=; b=ZeGzmp4ez3/4rNyR8wD9FEb8lILhghscZ1gI9NPMmVEP1bdrF2F0dqngv0faFZqKJ52Yvt IMmt4Riltkkl5SQy1LcxtkBBNJy/4Xrg0xQ+Jzpa7GgUYWpN9nHUC/maFZgClgkDoRkaTA D5L38LJiqpRlVsSOIJ88TltfjUM81oOiljodf8dCKEtJgqNqy3825ddtu36Up/Kt/1hFot i2zlaqbpeziQvFaIIQDHHZ/Uk6yccHnIKTX9iGk2n2I6d056qqpetV2vFWa7NlQdrW+h/N LVw8ZmyVAuM6TeR8/HjhLCmtM3iWtxwapU05x2mqSTijheydsCmBvuJrLuzdgg== MIME-Version: 1.0 Date: Thu, 10 Sep 2026 20:42:22 +0200 From: Nicolai Buchwitz To: Maxime Chevallier Cc: Andrew Lunn , davem@davemloft.net, Eric Dumazet , Jakub Kicinski , Paolo Abeni , Russell King , Heiner Kallweit , =?UTF-8?Q?Alexis_Lothor=C3=A9?= , Maxime Coquelin , Alexandre Torgue , Emil Renner Berthing , Minda Chen , Neil Armstrong , Kevin Hilman , Jerome Brunet , Martin Blumenstingl , Jan Petrous , Ovidiu Panait , Jose.Abreu@synopsys.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, thomas.petazzoni@bootlin.com, linux-arm-kernel@lists.infradead.org, linux-stm32@st-md-mailman.stormreply.com, PKneuper@dspace.de, David Laight Subject: Re: [PATCH net v2 5/6] net: stmmac: size the RX buffers from the frame length, not the MTU In-Reply-To: <20260910151404.976753-6-maxime.chevallier@bootlin.com> References: <20260910151404.976753-1-maxime.chevallier@bootlin.com> <20260910151404.976753-6-maxime.chevallier@bootlin.com> Message-ID: <2489a0482751f06eb4da702987c717e5@tipi-net.de> X-Sender: nb@tipi-net.de Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit X-Last-TLS-Session-Version: TLSv1.3 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260910_114235_386492_3FCC860E X-CRM114-Status: GOOD ( 21.15 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 10.9.2026 17:14, Maxime Chevallier wrote: > When picking the buffsize to use based on the MTU, we shouldn't check > only the MTU value, but also : > - ETH_HLEN for the L2 header, > - up to 2 VLAN tags, > - the FCS, > - the NET_IP_ALIGN > > The default bufsize is 1536 bytes, which is enough to contain all the > above so this hasn't surfaced before, but the addition of NET_IP_ALIGN > to the start of buffer address tripped the Jumbo selftest, leading to > this discovery. > > With that, we don't need the '>=' checks on the buffer len, we can use > more consistent comparison operators in stmmac_set_bfsize. > > Fixes: 286a83721720 ("stmmac: add CHAINED descriptor mode support > (V4)") > Signed-off-by: Maxime Chevallier > --- > .../net/ethernet/stmicro/stmmac/stmmac_main.c | 20 ++++++++++--------- > 1 file changed, 11 insertions(+), 9 deletions(-) > > diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c > b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c > index 5fe7e95fdd34..3664a298574a 100644 > --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c > +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c > @@ -1536,17 +1536,17 @@ static unsigned int stmmac_rx_offset(struct > stmmac_priv *priv) > return NET_SKB_PAD + NET_IP_ALIGN; > } > > -static int stmmac_set_bfsize(int mtu) > +static int stmmac_set_bfsize(int len) > { > int ret; > > - if (mtu >= BUF_SIZE_8KiB) > + if (len > BUF_SIZE_8KiB) > ret = BUF_SIZE_16KiB; > - else if (mtu >= BUF_SIZE_4KiB) > + else if (len > BUF_SIZE_4KiB) > ret = BUF_SIZE_8KiB; > - else if (mtu >= BUF_SIZE_2KiB) > + else if (len > BUF_SIZE_2KiB) > ret = BUF_SIZE_4KiB; > - else if (mtu > DEFAULT_BUFSIZE) > + else if (len > DEFAULT_BUFSIZE) > ret = BUF_SIZE_2KiB; > else > ret = DEFAULT_BUFSIZE; > @@ -4063,7 +4063,7 @@ static struct stmmac_dma_conf * > stmmac_setup_dma_desc(struct stmmac_priv *priv, unsigned int mtu) > { > struct stmmac_dma_conf *dma_conf; > - int bfsize, ret; > + int bfsize, len, ret; > u8 chan; > > dma_conf = kzalloc_obj(*dma_conf); > @@ -4073,13 +4073,15 @@ stmmac_setup_dma_desc(struct stmmac_priv *priv, > unsigned int mtu) > return ERR_PTR(-ENOMEM); > } > > - /* Returns 0 or BUF_SIZE_16KiB if mtu > 8KiB and dwmac4 or ring mode > */ > - bfsize = stmmac_set_16kib_bfsize(priv, mtu); > + len = mtu + ETH_HLEN + 2 * VLAN_HLEN + ETH_FCS_LEN + NET_IP_ALIGN; > + > + /* Returns 0 or BUF_SIZE_16KiB if len > 8KiB and dwmac4 or ring mode > */ > + bfsize = stmmac_set_16kib_bfsize(priv, len); > if (bfsize < 0) > bfsize = 0; > > if (bfsize < BUF_SIZE_16KiB) > - bfsize = stmmac_set_bfsize(mtu); > + bfsize = stmmac_set_bfsize(len); > > dma_conf->dma_buf_sz = bfsize; > /* Chose the tx/rx size from the already defined one in the Reviewed-by: Nicolai Buchwitz Thanks, Nicolai