Re: [PATCH 09/16] tty: serial: 8250_dma: Add a TX trigger workaround for AM33xx

From: Sebastian Andrzej Siewior
Date: Thu Sep 25 2014 - 09:11:48 EST

* Peter Hurley | 2014-09-25 07:31:32 [-0400]:

>I just verified that GNU readline6 uses ioctl(TCSETSW, ...) to do the set_termios
>(which is the ioctl that libc should use for tcsetattr(TCSADRAIN)).
>Maybe this userspace is using a readline()-alike that has a bug by not using the
>correct tcsetattr() action?

set_termios() has an opt argument. While doing ":n" in vi I see two invocations
with "opt == 8" which stands for TCSETS.
browsing through vi's code I stumbled upon

|static void rawmode(void)
| tcsetattr_stdin_TCSANOW(&term_vi);
|int FAST_FUNC tcsetattr_stdin_TCSANOW(const struct termios *tp)
| return tcsetattr(STDIN_FILENO, TCSANOW, tp);

and this is probably what you meant. There is also
| static void cookmode(void)
| {
| fflush_all();
| tcsetattr_stdin_TCSANOW(&term_orig);
| }

However I don't see __tty_perform_flush() in kernel invoked.

>Or maybe the glibc-equivalent has the bug, and tcsetattr(TCSADRAIN) is not using

libc is "GNU C Library 2.20".

>Peter Hurley

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