On Thu, Nov 30, 2023 at 02:42:20PM +0000, Greg Kroah-Hartman wrote: > On Thu, Nov 30, 2023 at 03:36:21PM +0100, Oliver Neukum wrote: > > On 30.11.23 14:48, Greg Kroah-Hartman wrote: > > I am afraid I need to point out that usb-serial has been changed _this_ _year_ > > to return -ENOTTY. CDC-ACM being also in this situation unfortunately > > I need to decide between one of the alternatives. > > Ah, oops, then it should probably be changed back. Unless Johan, any > specific reason this was changed? Had to go back to lore to see why I changed this: https://lore.kernel.org/all/20230604123505.4661-1-johan@xxxxxxxxxx/ IIRC we had a user that was not expecting break signalling to only work with one of the two ports of a Silabs device without user space being notified about it. In the cover letter I mention that the intent of "commit 9e98966c7bb9 ("tty: rework break handling") from 2008 appears to be to allow missing support to be reported to user space". Reporting back an error also avoids waiting for the break period when a subdriver does not support break (i.e. as when a tty driver does not support break). The inconsistency was discussed and if this turns out to be an issue we can have the tty layer turn that -ENOTTY into 0 before returning: https://lore.kernel.org/all/ZH8a12ZYtA2RzEK_@xxxxxxxxxxxxxxxxxxxx/ I haven't heard from anyone noticing any issues so far though. Johan
