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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?vGu9a4rW6wGSYC4VGPXQKaO8rsEXcV9tgift36cF74l7QpYLHwyViM9v0RPX?= =?us-ascii?Q?y8+cfWSDIvagl4I5hUrYfkF93VXU7m6Rr0t6S9XpdVHahNAOwDKnVaUYNM4Z?= =?us-ascii?Q?+V51Dph8kHldKAomU8eP+A1Pw1dX95dx/LfjZg4gXZOEK+ekaRM7s72IxCFF?= =?us-ascii?Q?79RmHHd89oQ3brSgWm1aVawEFv93SEe1SWJPHaACJngXwcOfKh7iXj6OQBpK?= =?us-ascii?Q?SkLl5SBQFvOCiJ0b2AsDP4hjT2y3xg9nFoZJ6jyVrJGAl6ufsXUNbH3gphOL?= =?us-ascii?Q?MkqGgnedIE7HyvqHMqAf4t5p39XvBdIPlPkF45PbwC5ttCG7E56NQPYWhprq?= =?us-ascii?Q?FXbNpgjMAzT3qJyeH7R7we9zniFmedVuZL0vKhhlKCnxfHY7KAyGOwB40jV2?= =?us-ascii?Q?YrwOWUz6ThQg3sz2FJPTNE6zLQhccX5I27rd9ZF5L+Wbv7sH99zyfkRJ8l45?= =?us-ascii?Q?264ZuiKmuboUC6/aeOcuwQM8U0WCXJOkMpk+vnlGQNpvShE4aPF/MYt+xAeC?= =?us-ascii?Q?GutHmPpdqqmxAmeIRZOPNoB2UUNsYNMC+w7IUIPdmiGyzmKd2Cwy5yFV0w4+?= =?us-ascii?Q?GMgkHAAc5UiLETrfF/A6PfOBdMILCbRAl/JmOIpvEQGoDw4ZTf+SgjzKOWfN?= =?us-ascii?Q?xTJMJwex1rBiv5VH8UqsHdlvDQCmmOI/fM1aDebkHZd/zKN5wZxVVlvFljAu?= =?us-ascii?Q?A/gWFCn5b/uhKLJuuBEOqAGVfpyMI0wNexglH7DpxUaw75zLyPelBgxoYFZD?= =?us-ascii?Q?YfAYBT6iTG+CbdpbHjgcL22UnKeRTIQyBr33hFoGjZ5LmNwxYFCwE3ZzQzOK?= =?us-ascii?Q?VUhHUvNIQtGV/CJkpewGP8c5O7skNkOqJfcEXb3zHrXOrEDj+34qCrf6WOnT?= =?us-ascii?Q?PYQQxbiR3MlcVN0Rq/eBuU4xG/JndSyceNJrScDddLWHLWTbg3dIhkBYhVY9?= =?us-ascii?Q?kNzCwQqYENves/Ac2ajf/PQJY6IbVBe2PWRCaSgjRsnXHNHt5xigLrZgfm7E?= =?us-ascii?Q?dabk+9BksKVcFjcU6M9OlbUOd8/0oaq954eQI0asCLA+VxLbUUVL/2PWRLcq?= =?us-ascii?Q?QapB+gk567P8EdvuugM6zzO8XyHCbKU3K23UEA5bNwfutiroa/ixZSBTE38Q?= =?us-ascii?Q?Y+SxrnTWHk9S5RiJ2/NVHd054d5jbLGsNqmDxvVhnxFNcQ+jMwyj01Rst9w5?= =?us-ascii?Q?Qz/EB+aElAQI7eYIvMUckbxVBGsubUutixY5tKAo9Eo2/ahQurMvZVAik7wi?= =?us-ascii?Q?6wZ5XzL1TwEHE5NhLThnqp9jRuJZuvoXhIu9okMNtshlZqQRryvAioUe+mjm?= =?us-ascii?Q?WlJ3WSsnMA4qUV6LRNdNngYV/51XOtf/050ZfFbl9BaSig8435nVzTnQ0xKa?= =?us-ascii?Q?NnyCodX2/tPi90+CMrNz9oWKZ2oEgvvwYJOpgs0jH2tTZ7qc14L0qnd6pwAS?= =?us-ascii?Q?HLdTzjjQ+hNxiclPY5Qf+vEBW7CG+TUEZ2rbcGViYU+LSFVeXb3xHBnOdMbO?= =?us-ascii?Q?8Ey9AQgH+ZH/IAcrRCGlr6dXvCstwYxOwauDgvg1musiarsL1v0r9E8q2sZy?= =?us-ascii?Q?W1S32cSbgQwkn1UcJSXb5QY8UucKkUy5LLOv3b46Z465vQpoYXizDrfl7f2a?= =?us-ascii?Q?MF6QbkVxV916eh0YJfYUh/g=3D?= X-OriginatorOrg: vpitech.com X-MS-Exchange-CrossTenant-Network-Message-Id: b454469a-ab48-4991-23ac-08dad16fc3c1 X-MS-Exchange-CrossTenant-AuthSource: SA1P222MB0296.NAMP222.PROD.OUTLOOK.COM X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 28 Nov 2022 18:38:38.3542 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 130d6264-38b7-4474-a9bf-511ff1224fac X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: 90xSSjPNd3WGKJNEPP4xR80uDG5MWFPmrVrXhkXMuF2wvF2Njs4SstfokR22PDeJARsVfnULAX+7xpAMMsCPIg== X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH0P222MB0365 Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org On Monday, November 28, 2022 11:20:41 AM MST Russell King (Oracle) wrote: > What exactly do you think should be done when a baud rate of zero is > requested? I see two reasonable options: Leave the baud rate alone, or reset it to the default (i.e. 9600). In my opinion, either of those options is just fine. > The fact of the matter is that at hardware level, the UART takes a > clock, and divides that down. To get to a baud rate of zero, one > would need an infinitely large divisor, which (a) is impossible to > program into the hardware and (b) would trigger a divide-by-zero > error in the kernel. So, we have to choose something. > > That decision was made before my time, when Ted Ts'o was maintaining > what was the original serial.c 8250-based driver, and the behaviour > he adopted was to set a baud rate of 9600 when B0 was requested, > which is reasonable - 9600 baud is the default setting. > > POSIX (which is what we use to define the behaviour of the TTY layer, > or at least what we _used_ to) doesn't specify the behaviour of B0 > as the output rate, other than it shall cause the model control lines > to be deasserted. What baud rate you get on the line is unspecified, > and thus left up to the implementation. > > So basically, 9600 baud for B0 is the behaviour of the 8250 driver > going back to the very early Linux versions and that has become the > standard Linux implementation shared by a great many serial drivers. > In effect, it's almost a de-facto standard. That is really interesting, thanks for the explanation! I like the idea of having consistent behavior across the Linux serial drivers, so it seems to me that mapping B0 to B9600 in all drivers is the way to go. -Alex