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Sun, 30 Aug 2020 07:50:06 +0000 Date: Sun, 30 Aug 2020 10:49:58 +0300 From: Vadym Kochan To: David Miller Cc: kuba@kernel.org, jiri@mellanox.com, idosch@mellanox.com, andrew@lunn.ch, oleksandr.mazur@plvision.eu, serhiy.boiko@plvision.eu, serhiy.pshyk@plvision.eu, volodymyr.mytnyk@plvision.eu, taras.chornyi@plvision.eu, andrii.savka@plvision.eu, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, andy.shevchenko@gmail.com, mickeyr@marvell.com Subject: Re: [net-next v5 1/6] net: marvell: prestera: Add driver for Prestera family ASIC devices Message-ID: <20200830074958.GA2568@plvision.eu> References: <20200825122013.2844-2-vadym.kochan@plvision.eu> <20200825.172003.1417643181819895272.davem@davemloft.net> <20200826081744.GA2729@plvision.eu> <20200826.073446.971357864812593855.davem@davemloft.net> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200826.073446.971357864812593855.davem@davemloft.net> User-Agent: Mutt/1.9.4 (2018-02-28) X-ClientProxiedBy: AM7PR02CA0002.eurprd02.prod.outlook.com (2603:10a6:20b:100::12) To HE1P190MB0539.EURP190.PROD.OUTLOOK.COM (2603:10a6:7:56::28) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from plvision.eu (217.20.186.93) by AM7PR02CA0002.eurprd02.prod.outlook.com (2603:10a6:20b:100::12) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3326.19 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: GhFYvc706wn9eIseFpkbsUQXl8h8VXUhMZDIAQsCuYl0GoHkRw9mL5fnF2GfRPD4StRiIS5jGR1CdHyYHHIiyvp7xPfQLSR/i2MiW0RQj0PoFoB2U1Vfxak1FyHGvbEIgHGMFkFY47Q3RHfYggJu922nMFPWFFLiN5mF9gC/zotKM0hDdJsFiEa984zeiEvtxJsQg07hPbxGB1ysnq9oVQLWoucUE+Prhbn70OyDnA0txbP+1zzxlIxNBzQg7qmJ/KFHn2WkAisCm8+JT2/FXpITTUTGTOV6Ogm2afumJVp2f/nPNJ3QiGBjf/odETokvgjqMiCQtgV2c3ubK461346E5EmQDzYShQ0N/4yS/uVZBuMC+foVI3U2Ixo3F0CGlpiUncxqNhHL5TCEh64cxXbMvKmWGGF/yaH76MBjj75znCKo1zosHScIzvFF+0te9bIU4uUgVr2c+E6ymQN4sq+9FDryapb+1G/9RYRz4UCkS7gGCw3Br/qOZ28w5DFL/d6eOehk1c46I3Gnn3ViuPyLsZEsotekAnuHQ2uNkiuybHHHgBzs7YnoZCTdvBEu/rOcJCQFfAsDWBlEoWD2+kUDp+JEHh2DjbvyMLXTdjKdx3+2HRR+Ex6aai85KZTRDT8Gj55ivaol0sRQqq1xJw== X-OriginatorOrg: plvision.eu X-MS-Exchange-CrossTenant-Network-Message-Id: 1499e905-61b1-4dd8-6cbc-08d84cb94f4f X-MS-Exchange-CrossTenant-AuthSource: HE1P190MB0539.EURP190.PROD.OUTLOOK.COM X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 30 Aug 2020 07:50:06.2037 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 03707b74-30f3-46b6-a0e0-ff0a7438c9c4 X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: cSRZGrPUkU1WrL8gt7jmPkCBAD/MjYwjgwt4DbOJniir3etbOF6UaiGAurGl4OlhcZFHMWhpdNZVjAzqDqfbNaFL7Z3MsbflrvAGY4m2EpM= X-MS-Exchange-Transport-CrossTenantHeadersStamped: HE1P190MB0185 Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Hi David, On Wed, Aug 26, 2020 at 07:34:46AM -0700, David Miller wrote: > From: Vadym Kochan > Date: Wed, 26 Aug 2020 11:17:44 +0300 > > > Initially there was (in RFC patch set), not locking, but _rcu list API > > used, because the port list is modified only by 1 writer when creating > > the port or deleting it on switch uninit (the really theoretical case > > which might happen is that event might be received at that time which > > causes to loop over this list to find the port), as I understand > > correctly list_add_rcu is safe to use with no additional locking if there is 1 > > writer and many readers ? So can I use back this approach ? > > Are you really certain only one writer can exist at one time? Yes, list_add() is called on: prestera_pci_probe() -> prestera_device_register() -> prestera_switch_init() -> prestera_create_ports() and list_del() is called on: prestera_pci_remove() -> prestera_device_unregister() -> prestera_switch_fini() -> prestera_destroy_ports() in all other cases the port_list is used for port lookup on rx or when event is received from the fw. So I really think that at least RCU list API might be used or rw lock. In early version the ports were creating before fw event handlers registration, but in this version the ports are creating after event handlers are registered so it really needs locking. Regarding DMA comments, looks like I can get rid of those bounce buffer handling because swiotlb can handle this ? In that case looks like just DMA map/unmap and sync should be enough. Regards, Vadym Kochan