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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Maxime Coquelin , Alexandre Torgue , Maxime Chevallier , netdev@vger.kernel.org, linux-stm32@st-md-mailman.stormreply.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Matthew Gerlach References: <20251126-a10_ext_fix-v1-1-d163507f646f@altera.com> Content-Language: en-US From: "G Thomas, Rohan" In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: MA5P287CA0190.INDP287.PROD.OUTLOOK.COM (2603:1096:a01:1b6::14) To DM6PR03MB5371.namprd03.prod.outlook.com (2603:10b6:5:24c::21) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DM6PR03MB5371:EE_|IA3PR03MB8384:EE_ X-MS-Office365-Filtering-Correlation-Id: fac0edb2-657f-4a0d-cf33-08de2cb24c8b X-MS-Exchange-AtpMessageProperties: SA X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|376014|7416014; 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This results >> in buffering of a few frames in the FIFO without triggering Rx DMA >> from transferring the data to the system memory until another packet >> is received. Once the issue happens, for a ping request, the packet is >> forwarded to the system memory only after we receive another packet >> and hece we observe a latency equivalent to the ping interval. >> >> 64 bytes from 192.168.2.100: seq=1 ttl=64 time=1000.344 ms >> >> Also, we can observe constant gmacgrp_debug register value of >> 0x00000120, which indicates "Reading frame data". >> >> The issue is not reproducible after disabling frame flushing when Rx >> buffer is unavailable. But in that case, the Rx DMA enters a suspend >> state due to buffer unavailability. To resume operation, software >> must write to the receive_poll_demand register after adding new >> descriptors, which reactivates the Rx DMA. > > > This seems like a sensible writeup, which all seems to make sense, > even though the databook I have seems vague on the effect of the > DFF bit. > >> This issue is observed in the socfpga platforms which has dwmac1000 IP >> like Arria 10, Cyclone V and Agilex 7. Issue is reproducible after >> running iperf3 server at the DUT for UDP lower packet sizes. >> >> Signed-off-by: Rohan G Thomas >> Reviewed-by: Matthew Gerlach > > Given the above, that Maxime has also tested it which shows a net > benefit, and I've looked through this, even though I can't positively > say it's correct due to the databook vagueness: > > Reviewed-by: Russell King (Oracle) > > Thanks! > Thanks for reviewing the patch. Best Regards, Rohan