linux-kernel - Re: [PATH RESEND v2 03/10] tty: xuartps: Always enable transmitter in start

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Date:	Fri, 20 Nov 2015 07:28:49 -0800
From:	Sören Brinkmann <soren.brinkmann@...inx.com>
To:	Peter Hurley <peter@...leysoftware.com>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.com>,
	<linux-arm-kernel@...ts.infradead.org>,
	Michal Simek <michal.simek@...inx.com>,
	<linux-serial@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATH RESEND v2 03/10] tty: xuartps: Always enable transmitter
 in start_tx

Hi Peter,

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 state 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?

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 trying
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 simply
says "Start transmitting characters." for start_tx(). Hence, I thought,
this function is probably supposed to just do that and start the
transmitter. I'll test whether this patch can be dropped.

	Thanks,
	Sören
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