Re: [PATH RESEND v2 03/10] tty: xuartps: Always enable transmitter in start_tx

From: Peter Hurley
Date: Fri Nov 20 2015 - 12:12:37 EST

On 11/20/2015 12:05 PM, SÃren 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 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?
> Fixing up the patch, I looked at this one. It might actually do that.


> Without having changed anything. The doc says: "The driver should
> stop transmitting characters as soon as possible.". And the
> implementation is really not draining any FIFO, but just disabling the
> transmitter. I take your question as that this might not be this way?
> Should stop_tx drain the FIFO first?


Most h/w can't actually stop the transmitter (or not without losing
data), so that's why the expectation is only for "as soon as possible".
Stopping sooner is better.

Peter Hurley

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