From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751320AbdCQM2p (ORCPT ); Fri, 17 Mar 2017 08:28:45 -0400 Received: from mail-it0-f50.google.com ([209.85.214.50]:35918 "EHLO mail-it0-f50.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751151AbdCQM2m (ORCPT ); Fri, 17 Mar 2017 08:28:42 -0400 MIME-Version: 1.0 From: Geert Uytterhoeven Date: Fri, 17 Mar 2017 13:28:39 +0100 X-Google-Sender-Auth: vKF8QhTj1DmfxvOhZLbYrc_96ls Message-ID: Subject: Expected behavior of set_termios() w.r.t. TX FIFO? To: Greg KH , Jiri Slaby , Peter Hurley Cc: "linux-serial@vger.kernel.org" , "linux-kernel@vger.kernel.org" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Greg, Jiri, Peter, I'm wondering what is the expected behavior of calling uart_ops.set_termios() w.r.t. characters that are already queued in the UART's TX FIFO. - Should it wait (block) until all queued characters have been transmitted, before changing the UART's settings? - Should it apply the new settings immediately, affecting the already queued characters? - Should it apply the new settings, dropping the already queued characters? - Is calling uart_ops.set_termios() while the TX FIFO isn't empty allowed (this can be triggered easily from userspace)? uart_ops.set_termios() returns void, so there's no way to return an error. Currently the sh-sci driver blocks until the TX FIFO has been emptied, which may never happen if hardware flow control is enabled, and the remote side never asserts CTS, leading to: NMI watchdog: BUG: soft lockup - CPU#0 stuck for 22s! See also "[PATCH 2/2] serial: sh-sci: Fix hang in sci_reset()", https://lkml.org/lkml/2016/12/2/225). Thanks for your answer! Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds