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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Maxime Coquelin , xfr@outlook.com, "linux-tegra@vger.kernel.org" Subject: Re: [PATCH net-next v3 1/4] net: stmmac: Switch to zero-copy in non-XDP RX path Message-ID: References: <20250124003501.5fff00bc@orangepi5-plus> <20250124104256.00007d23@gmail.com> <20250125224342.00006ced@gmail.com> <20250126183714.00005068@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250126183714.00005068@gmail.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250126_033554_720361_51A909EF X-CRM114-Status: UNSURE ( 9.54 ) X-CRM114-Notice: Please train this message. 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 Sun, Jan 26, 2025 at 06:37:14PM +0800, Furong Xu wrote: > The "SPH feature" splits header into buf->page (non-zero offset) and > splits payload into buf->sec_page (zero offset). > > For buf->page, pp_params.max_len should be the size of L3/L4 header, > and with a offset of NET_SKB_PAD. > > For buf->sec_page, pp_params.max_len should be dma_conf->dma_buf_sz, > and with a offset of 0. > > This is always true: > sizeof(L3/L4 header) + NET_SKB_PAD < dma_conf->dma_buf_sz + 0 Thanks, understood, but are there situations where the device is unable to split a packet? For example, a large L2 packet. I am trying to understand if there are situations where the device will write more than "dma_conf->dma_buf_sz - NET_SKB_PAD" to the head buffer.