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

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On 11/20/2015 12:05 PM, Sören 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.

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



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[PATH RESEND v2 00/10] tty: xuartps: Fix lock ups Soren Brinkmann <soren.brinkmann@xilinx.com> - 2015-11-19 21:20 +0100
  [PATH RESEND v2 03/10] tty: xuartps: Always enable transmitter in start_tx Soren Brinkmann <soren.brinkmann@xilinx.com> - 2015-11-19 21:20 +0100
    Re: [PATH RESEND v2 03/10] tty: xuartps: Always enable transmitter in  start_tx Peter Hurley <peter@hurleysoftware.com> - 2015-11-20 13:20 +0100
      Re: [PATH RESEND v2 03/10] tty: xuartps: Always enable transmitter  in start_tx Sören Brinkmann <soren.brinkmann@xilinx.com> - 2015-11-20 16:30 +0100
        Re: [PATH RESEND v2 03/10] tty: xuartps: Always enable transmitter in  start_tx Peter Hurley <peter@hurleysoftware.com> - 2015-11-20 17:40 +0100
          Re: [PATH RESEND v2 03/10] tty: xuartps: Always enable transmitter  in start_tx Sören Brinkmann <soren.brinkmann@xilinx.com> - 2015-11-20 18:00 +0100
            Re: [PATH RESEND v2 03/10] tty: xuartps: Always enable transmitter in  start_tx Peter Hurley <peter@hurleysoftware.com> - 2015-11-20 18:20 +0100
              Re: [PATH RESEND v2 03/10] tty: xuartps: Always enable transmitter  in start_tx Sören Brinkmann <soren.brinkmann@xilinx.com> - 2015-11-20 18:30 +0100
              Re: [PATH RESEND v2 03/10] tty: xuartps: Always enable transmitter in  start_tx Michal Simek <michal.simek@xilinx.com> - 2015-11-23 08:10 +0100
                Re: [PATH RESEND v2 03/10] tty: xuartps: Always enable transmitter in  start_tx Peter Hurley <peter@hurleysoftware.com> - 2015-11-23 21:10 +0100
                Re: [PATH RESEND v2 03/10] tty: xuartps: Always enable transmitter in  start_tx Michal Simek <michal.simek@xilinx.com> - 2015-11-24 08:50 +0100
      Re: [PATH RESEND v2 03/10] tty: xuartps: Always enable transmitter  in start_tx Sören Brinkmann <soren.brinkmann@xilinx.com> - 2015-11-20 18:10 +0100
        Re: [PATH RESEND v2 03/10] tty: xuartps: Always enable transmitter in  start_tx Peter Hurley <peter@hurleysoftware.com> - 2015-11-20 18:20 +0100
  [PATH RESEND v2 05/10] tty: xuartps: Improve startup function Soren Brinkmann <soren.brinkmann@xilinx.com> - 2015-11-19 21:20 +0100
  [PATH RESEND v2 08/10] tty: xuartps: Move RX path into helper function Soren Brinkmann <soren.brinkmann@xilinx.com> - 2015-11-19 21:20 +0100
  [PATH RESEND v2 06/10] tty: xuartps: Keep lock for whole ISR Soren Brinkmann <soren.brinkmann@xilinx.com> - 2015-11-19 21:20 +0100
  [PATH RESEND v2 09/10] tty: xuartps: Only handle RX IRQs when RX is enabled Soren Brinkmann <soren.brinkmann@xilinx.com> - 2015-11-19 21:20 +0100
  [PATH RESEND v2 10/10] tty: xuartps: Cleanup: Reformat if-else Soren Brinkmann <soren.brinkmann@xilinx.com> - 2015-11-19 21:20 +0100
  [PATH RESEND v2 07/10] tty: xuartps: Acquire port lock for shutdown Soren Brinkmann <soren.brinkmann@xilinx.com> - 2015-11-19 21:20 +0100
  [PATH RESEND v2 01/10] tty: xuartps: Beautify read-modify writes Soren Brinkmann <soren.brinkmann@xilinx.com> - 2015-11-19 21:20 +0100
  [PATH RESEND v2 02/10] tty: xuartps: Use spinlock to serialize HW access Soren Brinkmann <soren.brinkmann@xilinx.com> - 2015-11-19 21:20 +0100

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