From mboxrd@z Thu Jan  1 00:00:00 1970
From: =?utf-8?B?U8O2cmVu?= Brinkmann <soren.brinkmann@xilinx.com>
Subject: Re: [PATH RESEND v2 03/10] tty: xuartps: Always enable transmitter
 in start_tx
Date: Fri, 20 Nov 2015 08:58:04 -0800
Message-ID: <20151120165804.GV32017@xsjsorenbubuntu>
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 <564F0E75.5020100@hurleysoftware.com>
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To: Peter Hurley <peter@hurleysoftware.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Jiri Slaby <jslaby@suse.com>, linux-arm-kernel@lists.infradead.org, Michal Simek <michal.simek@xilinx.com>, linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org
List-Id: linux-serial@vger.kernel.org

Hi Peter,

On Fri, 2015-11-20 at 11:30AM -0500, Peter Hurley wrote:
> Hi S=C3=B6ren,
>=20
> On 11/20/2015 10:28 AM, S=C3=B6ren Brinkmann wrote:
> > On Fri, 2015-11-20 at 07:13AM -0500, Peter Hurley wrote:
> >> On 11/19/2015 03:02 PM, Soren Brinkmann wrote:
> >>> start_tx must start transmitting characters. Regardless of the st=
ate of
> >>> the circular buffer, always enable the transmitter hardware.
> >>
> >> Why?
> >>
> >> Does cdns_uart_stop_tx() actually stop the transmitter so that
> >> data remains in the transmitter?
> >=20
> > Well, I saw my system freezing and the cause seemed to be that the =
UART
> > receiver and/or transmitters were disabled while the system was try=
ing
> > to print. Hence, I started questioning all locations touching the
> > transmitter/receiver enable. I read the docs in
> > https://www.kernel.org/doc/Documentation/serial/driver, which simpl=
y
> > says "Start transmitting characters." for start_tx(). Hence, I thou=
ght,
> > this function is probably supposed to just do that and start the
> > transmitter. I'll test whether this patch can be dropped.
>=20
> I don't think that patch would fix any freeze problems, but restartin=
g
> the transmitter even if the circ buffer is empty may be necessary to
> push out remaining data when the port is restarted after being stoppe=
d.
>=20
> IOW, something like
>=20
> 	if (uart_tx_stopped(port))
> 		return;
>=20
> 	....
>=20
>=20
> 	if (uart_circ_empty(&port->state->xmit)
> 		return;

Thanks! I'll change the patch accordingly.

>=20
>=20
> Below is a (work-in-progress) serial driver validation test for flow
> control handling (it may need some tuning for slow line speeds).
> Usual caveats apply. Takes ~40secs @ 115200.

I'll try to get that running on my system.

	Thanks,
	S=C3=B6ren