On 11/20/2015 12:05 PM, S?ren Brinkmann wrote:

On Fri, 2015-11-20 at 07:13AM -0500, Peter Hurley wrote:

quoted

On 11/19/2015 03:02 PM, Soren Brinkmann wrote:

quoted

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.

Ok.

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?

No.

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.

Regards,
Peter Hurley