linux-kernel - Re: [PATCH] usb-serial: Fix usb serial console open/close regression

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Message-ID: <Pine.LNX.4.44L0.1003081028400.1596-100000@iolanthe.rowland.org>
Date:	Mon, 8 Mar 2010 10:35:37 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Jason Wessel <jason.wessel@...driver.com>
cc:	Greg Kroah-Hartman <gregkh@...e.de>,
	Alan Cox <alan@...ux.intel.com>,
	Oliver Neukum <oliver@...kum.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb-serial: Fix usb serial console open/close regression

On Mon, 8 Mar 2010, Jason Wessel wrote:

> Commit e1108a63e10d344284011cccc06328b2cd3e5da3 ("usb_serial: Use the
> shutdown() operation") breaks the ability to use a usb console
> starting in 2.6.32.  This was observed when using
> console=ttyUSB0,115200 as a boot argument with an FTDI device.  The
> error is:
> 
> ftdi_sio ttyUSB0: ftdi_submit_read_urb - failed submitting read urb, error -22
> 
> The handling of the ASYNCB_INITIALIZED changed in 2.6.32 such that in
> tty_port_shutdown() it always clears the flag if it is set.  As a work
> around the usb console must reset this flag, in order for the hw to
> stay open.
> 
> CC: Greg Kroah-Hartman <gregkh@...e.de>
> CC: Alan Cox <alan@...ux.intel.com>
> CC: Alan Stern <stern@...land.harvard.edu>
> CC: Oliver Neukum <oliver@...kum.org>
> CC: Andrew Morton <akpm@...ux-foundation.org>
> CC: linux-usb@...r.kernel.org
> CC: linux-kernel@...r.kernel.org
> Signed-off-by: Jason Wessel <jason.wessel@...driver.com>
> 
> ---
>  drivers/usb/serial/usb-serial.c |    7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> --- a/drivers/usb/serial/usb-serial.c
> +++ b/drivers/usb/serial/usb-serial.c
> @@ -287,10 +287,13 @@ static void serial_down(struct tty_port 
>  	struct usb_serial_driver *drv = port->serial->type;
>  	/*
>  	 * The console is magical.  Do not hang up the console hardware
> -	 * or there will be tears.
> +	 * or there will be tears.  If this is a console the initialized
> +	 * flag is reset.
>  	 */
> -	if (port->console)
> +	if (port->console) {
> +		set_bit(ASYNCB_INITIALIZED, &port->port.flags);
>  		return;
> +	}
>  	if (drv->close)
>  		drv->close(port);
>  }

This is a little unfortunate.  It would be better to prevent
tty_port_shutdown() from clearing ASYNCB_INITIALIZED in the first
place.  The problem is that the tty core doesn't know when the port is
being used as a console.  There ought to be a way to tell it.

Alan Stern

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