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Rozycki" To: Mikulas Patocka cc: Greg Kroah-Hartman , Richard Henderson , Ivan Kokshaysky , Matt Turner , linux-alpha@vger.kernel.org, Arnd Bergmann , linux-serial@vger.kernel.org, linux-rtc@vger.kernel.org Subject: Re: [PATCH 2/2 v4] alpha: add a delay before serial port read In-Reply-To: Message-ID: References: <20200506114711.GB3024358@kroah.com> <20200506154938.GA3537174@kroah.com> <20200506160823.GA3559699@kroah.com> <20200506174528.GB3711921@kroah.com> Content-Type: text/plain; charset=US-ASCII X-ReSent-Date: Wed, 13 May 2020 23:34:55 +0100 (BST) X-Resent-Sender: "Maciej W. Rozycki" X-ReSent-From: "Maciej W. Rozycki" X-ReSent-To: "Maciej W. Rozycki" X-ReSent-Subject: Re: [PATCH 2/2 v4] alpha: add a delay before serial port read X-ReSent-Message-ID: X-Return-Path: macro@linux-mips.org X-MS-Exchange-Organization-ExpirationStartTime: 13 May 2020 22:35:12.5748 (UTC) X-MS-Exchange-Organization-ExpirationStartTimeReason: OriginalSubmit X-MS-Exchange-Organization-ExpirationInterval: 1:00:00:00.0000000 X-MS-Exchange-Organization-ExpirationIntervalReason: OriginalSubmit X-MS-Exchange-Organization-Network-Message-Id: 10a032b3-ef12-4d4a-080c-08d7f78de67f X-EOPAttributedMessage: 0 X-MS-Exchange-Organization-MessageDirectionality: Originating X-MS-Office365-Filtering-HT: Tenant X-Forefront-Antispam-Report: CIP:216.71.154.42;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:esa4.hgst.iphmx.com;PTR:esa4.hgst.iphmx.com;CAT:NONE;SFTY:;SFS:(4636009)(33430700002)(4326008)(107886003)(5660300002)(86362001)(6666004)(42186006)(82310400002)(6862004)(336012)(26005)(8936002)(356005)(1096003)(7636003)(8676002)(7596003)(54906003)(33440700001)(34756004)(1736002);DIR:INB;SFP:; X-MS-PublicTrafficType: Email X-MS-Exchange-Organization-AuthSource: BN3NAM04FT016.eop-NAM04.prod.protection.outlook.com X-MS-Exchange-Organization-AuthAs: Anonymous X-OriginatorOrg: sharedspace.onmicrosoft.com X-MS-Office365-Filtering-Correlation-Id: 10a032b3-ef12-4d4a-080c-08d7f78de67f X-MS-TrafficTypeDiagnostic: MWHPR04MB0545: X-MS-Oob-TLC-OOBClassifiers: OLM:8882; X-MS-Exchange-Organization-SCL: 1 X-Microsoft-Antispam: BCL:0; X-MS-Exchange-CrossTenant-OriginalArrivalTime: 13 May 2020 22:35:12.2890 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 10a032b3-ef12-4d4a-080c-08d7f78de67f X-MS-Exchange-CrossTenant-Id: b61c8803-16f3-4c35-9b17-6f65f441df86 X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=b61c8803-16f3-4c35-9b17-6f65f441df86;Ip=[216.71.154.42];Helo=[esa4.hgst.iphmx.com] X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: MWHPR04MB0545 X-MS-Exchange-Transport-EndToEndLatency: 00:00:01.9520855 X-MS-Exchange-Processed-By-BccFoldering: 15.20.2979.027 X-Microsoft-Antispam-Mailbox-Delivery: ucf:1;jmr:0;auth:0;dest:C;OFR:CustomRules;ENG:(20160514016)(750127)(520002050)(944506383)(944626516); X-Microsoft-Antispam-Message-Info: =?us-ascii?Q?GMwzOavDzojTgLwA50Ysm/iBpIvh5SPmlW4ReQemyp83RQtj//BaKo1Cikyv?= =?us-ascii?Q?LcroNGqEaLUqRtlihuVMWBHpE2Ufgp/OBwuKFbh+FYGgBvZOBnQ3BOi+fsKi?= =?us-ascii?Q?9OGHRVI8oIB46bCX+VBGynHCB7YveOkPO9MWHsL+XJvaZMtxZPAAWE+sXAz1?= =?us-ascii?Q?PGQ44IAafuVtSbPzxQxLjnEFdIPQhfC76zRmupTpX1DbBdmD0EZwpfWPzeym?= =?us-ascii?Q?IEDyE9TyFXUg58cQZRmgHyxI+0o/bANtGx5uqR8L5EoR48ugEXjgO7YjLPGU?= =?us-ascii?Q?51m2JdPfpuPX6T8RsoFBwUFEex0JU6zGwQl8I7GRPOG6ZkyT9POfm4012IFE?= =?us-ascii?Q?YBLkgQe07KoIZ5MFe/LxsnBBis92z9tw2Yjf3gs8JXj0g3RXvG5uIYM/qFI+?= =?us-ascii?Q?LzzB8lrvlCsfHfzz2quSFZGrILey3EnhJn56Ty8j7NXs9t325tsM7obDQkHw?= =?us-ascii?Q?XZoMw460I3e/YW5qAMx3W2qkHZPK+K3W9lTUuxTdzyofEdDzrcICbnXS3sML?= =?us-ascii?Q?7SVPn6hapRmOSZqv8ZU8E4fr7G0y9OUpiPzh61ddScM1DEblCWesPQopEME+?= =?us-ascii?Q?udg7vGm5LnPJn2dR7JXgNZB603fZCPNfojUZc+rLCr0bBb7RrIuADeuQI4PF?= =?us-ascii?Q?ERwtzuvNhwYaPlZvqbbsI2UKzkvbuPv/IyFMlTZQ4PYS2xqDdcd/sXq1+a8W?= =?us-ascii?Q?uFgx05wY4aP+l5j845I3q7hhX8xBcEIGUAHLovRR6MWf+2uTaJFv0TkD9OrH?= =?us-ascii?Q?2Rw5LWVKpEXDjnCybw8v4cyrC5ekum625apMxx9zvugpcZDznQoOBg2Pykn3?= =?us-ascii?Q?qCzKXyYdJH/wG+iXLJ6Ypxjj1I2Yh3LOYcajN+TnH6n6676sh/S9yEdXiva8?= =?us-ascii?Q?O7TBhBhJH/k6WfvGo/9SLc/D9J4/eN1VO6kca7Q5/31Pqv54ImSRC9sRfNlU?= =?us-ascii?Q?vsCZERd3RaRigo3ObzsnZJIPD9XEISVX4/fNdvnVfApWz/8HS5zFPBQZLzWl?= =?us-ascii?Q?fQSFThNS7u9SohEutJQNcQxWN9AGaSQkcpNgBlYSIQMfg/3B4oJu7IU2+9DI?= =?us-ascii?Q?TLsocKO4FBwxgEEfnIwvu5MxBPbe/4a+W9H89JcMfCf7NqQduS6WaaKsLVyf?= =?us-ascii?Q?hDjp6kb+/xPnTiEt0b2BqeFBTEQnZ6Xsgm/Tc62N0wc5dj41STUpZJ2LZDgX?= =?us-ascii?Q?s8A1V6vLVc+GEA5IhdrUwoebdUs6AiZTzRdwWbzRGSO6HwW7JeF7C/sRmz0h?= =?us-ascii?Q?jBh6+A10u9zkTixaQUukfUd19laHFXk7/uZKNXDmfSu2Iux7tPYU5Vg0CrMr?= =?us-ascii?Q?5zcW3dYxunGYTIvDlKVQFXKmzgljwgmQgVm+jI6EaLb8PFGLXQbOYWN/8WLX?= =?us-ascii?Q?o6ZwWGlco4N7pxqiG620+oKCvsSehlJzqXqUmumbMNhtpVPSDwUc2rTFFWWf?= =?us-ascii?Q?PkoUKRakFxD8CxJvEheQx4pvb/vCmOsW?= MIME-Version: 1.0 Sender: linux-rtc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-rtc@vger.kernel.org On Thu, 7 May 2020, Mikulas Patocka wrote: > > > I've created this patch that adds a global macro/variable > > > serial_port_needs_delay. I've also deleted UPQ_DELAY_BEFORE_READ and test > > > serial_port_needs_delay directly in io_serial_in, so that the compiler > > > will optimize it out on non-alpha architectures. > > > > That's not good, what about systems with hundreds of serial ports? > > I doubt that someone will conect hundreds of serial ports to such an old > alpha machine :) It would be good if PCI serial ports (on add-on cards) were unaffected. > > > > But, there is no other way to detect this based on hardware > > > > signatures/types instead? That is usually the best way to do it, right? > > > > > > It's hard to detect Alpha without using '#ifdef CONFIG_ALPHA' :) The ISA > > > serial port hardware is simple, so I think that you can't distinguish it > > > just based on its behavior. > > > > The ISA serial port hardware does not have a unique vendor/product id > > somewhere? Some other sort of definition that we can use to determine > > exactly what type of system we are running on? > > AFAIK it doesn't. You can only distinguish 8250, 16550 and 16550A - but > not the vendor. You might be able to handle it as a platform device. It's an onboard peripheral after all and wired permanently subject to further run-time configuration. Otherwise it's a generic off-the-shelf pre-LPC-bus PC Super I/O chip. Even if we can detect it it'll be there on some x86 machine. And the issue is a problem that may well be anywhere between the CPU, the northbridge, the southbridge and the Super I/O, and the weak MMIO ordering of the Alpha CPU does not help narrowing it down. Let me see... It's an NS PC87332 piece. For Avanti technical spec see: and for the National Semiconductor piece search for "PC87332.pdf" (no direct link, but you can download it indirectly): 2.5.8 SuperI/O Identification Register (SID, Index = 08h) The SID Register is accessed, like the other configuration registers, through the Index Register. This read-only register is used to identify the PC87332 device. 7 6 5 4 3 2 1 0 0 0 0 1 X X X X Super I/O Identification Reg. (SID) Index = 08h I'm not sure how reliable the uniqueness of the four bits in the SID register is across various PC Super I/O chips. I doubt that the chip has any observable issues with our serial driver on x86 systems though. I'm not sure if the situation is fully understood here, but we have a regression and a working solution now is better than a perfect one in the unspecified future. We can always improve once we get to the bottom of the issue. I'm in lockdown away from my Alpha machine, but I can try verifying the solution, also with PCI/e serial ports once I am out of lockdown and back the right home sometime. Maciej