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SubjectRe: [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@suse.de>
> CC: Alan Cox <alan@linux.intel.com>
> CC: Alan Stern <stern@rowland.harvard.edu>
> CC: Oliver Neukum <oliver@neukum.org>
> CC: Andrew Morton <akpm@linux-foundation.org>
> CC: linux-usb@vger.kernel.org
> CC: linux-kernel@vger.kernel.org
> Signed-off-by: Jason Wessel <jason.wessel@windriver.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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