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

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Date:	Thu, 25 Sep 2014 15:11:37 +0200
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	Peter Hurley <peter@...leysoftware.com>
Cc:	Frans Klaver <frans.klaver@...ns.com>,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	tony@...mide.com, gregkh@...uxfoundation.org,
	linux-kernel@...r.kernel.org, balbi@...com,
	linux-serial@...r.kernel.org, linux-omap@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Alan Cox <alan@...ux.intel.com>
Subject: Re: [PATCH 09/16] tty: serial: 8250_dma: Add a TX trigger workaround
 for AM33xx

* 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
>ioctl(TCSETSW)?

libc is "GNU C Library 2.20". 

>Regards,
>Peter Hurley

Sebastian
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