linux-kernel - Re: [PATCH] serial: revert "Use block_til

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Message-ID: <20100621151309.334f6645@lxorguk.ukuu.org.uk>
Date:	Mon, 21 Jun 2010 15:13:09 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Tony Luck <tony.luck@...el.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org, Greg KH <gregkh@...e.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	John Kacur <jkacur@...hat.com>,
	Al Viro <viro@...iv.linux.org.uk>, Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] serial: revert "Use block_til_ready helper"

> The way that the output is garbled seems to be just missing characters,
> in a mostly reproducible way. Repeatedly writing the string
> abcdefghijklmnopqrstuvwxyz1234567890 into ttyS0 gives an output like
> 'akq7m3iy', where only every sixteenth character is shown, plus
> an extra character in the second position.

Ok this sort of makes sense. Something isn't getting initialised and both
getty and minicom will do a termios set which is sorting it out.


And this is occurring because the generic block_til_ready sets
ASYNCB_NORMAL_ACTIVE so the termios updating gets skipped.

Ok the quickfix for this kernel is to delete this

       /*
         * If this is the first open to succeed, adjust things to suit.
         */
        if (retval == 0 && !(port->flags & ASYNC_NORMAL_ACTIVE)) {
                set_bit(ASYNCB_NORMAL_ACTIVE, &port->flags);

                uart_update_termios(state);
        }

and paste it into

void tty_port_raise_dtr_rts(struct tty_port *port)
{
        if (port->ops->dtr_rts)
                port->ops->dtr_rts(port, 1);

		-->> HERE <<--
}


(the mutex is held by the caller)

That should cure it and then we can think about doing it more elegantly
by getting the serial layer to use tty_port_open, kfifo and the like and
removing the tons of repeated crap in all the drivers.

Alan
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