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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: <20250126205625.00006d64@gmail.com> In-Reply-To: References: <20250124003501.5fff00bc@orangepi5-plus> <20250124104256.00007d23@gmail.com> <20250125224342.00006ced@gmail.com> <20250126183714.00005068@gmail.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Sun, 26 Jan 2025 13:35:45 +0200, Ido Schimmel wrote: > 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. Nice catch! When receiving a large L2/non-IP packet, more than "dma_conf->dma_buf_sz - NET_SKB_PAD" will be written. So we should: pp_params.max_len = dma_conf->dma_buf_sz + stmmac_rx_offset(priv); Thanks a lot, Ido Have a nice weekend :)